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  1. 177 points
    Seeing as it's nice and early in the day, perhaps we can see the remainder of Saturday through without the hysterics expressed on the forum yesterday? Critical points of note are simple: 1. Amplified upper pattern remains favourable for (two) trough disruption(s) early-mid next week 2. Scope of how and where these may occur will NOT be correctly resolved in ANY model at this lead time 3. Ergo, any over-analysis is pointless at this lead time given great uncertainty and variance/volatility in model handling 4. Likely erratic and eventually weakening E'ward progress of occlusion into cold air Tues means uncertainty on areal spread of snow: GFS PPN phase charts to be viewed with due caution. 5. Risk of rain onto frozen surfaces even where no snow. Varied wintry hazards look inevitable but no compelling evidence for a 'nationwide snow event' in strict defined sense. However, threat of disruptive snow for some areas (starting in parts of NI initially under frontal mass ascent; then W Scotland and Wales) is quite obvious, although no regional detail is reliable for now. 6. The potential for some easterly flow later into the week could not be *wholly* discounted yesterday (despite some claiming so); nor again in this morning's output, albeit still considered a lower probability outcome (ca. 40% support for some easterly component in 00z MOGREPS-G) 7. Attempt to resume westerly mobility later in the week (Weds-Thurs, powered by strong jet) may threaten further snow with second trough disruption. Importantly, the transition/timing and evolution of this switch will inevitably be messy and poorly resolved in all models currently. 8. Further swings in output are a given, as models struggle with upstream driving developments in W Atlantic/US. 9. Thus, can we desist from further forum freak-outs today...! :-)
  2. 122 points
    My retired colleague Ian McCaskill, RIP, would have relished discussing this Christmas Kerfuffle on-air with typical humour. GFS 12z deterministic very similar in final reaches of run to Thursdays ECMWF Monthly broadscale set-up for same period just after Christmas. Whether that will remain so tonight, we shall see....
  3. 121 points
    An ode to the model output thread... "In days of old, when Thatcher was bold and Kettley was a weatherman, Tales are told of winters cold, and snow lay everywhere, man. The World Wide Web and ECM were yet to be invented And weather forecasts at the time were often quite demented! But there's no doubt, the records show, that winters then were colder And five foot drifts were commonplace - they came up to your shoulder! For years and years all we've had is windy wet and mild And although it's not all been bad we crave a winter wild.... Now... The models hint that Scandinavia could maintain a block To curb Atlantics bad behaviour - that would really rock! But... The GEM can't be trusted; the GFS is dire The ECM has often busted; the CFS? - a liar! So on UKMO we must rely but wait - is it cursed? More runs needed, standing by.... let's get the cold in first! Hope you all have a great weekend of model watching!
  4. 116 points
    Evening All- Ive not replied to anything today- so sorry if ive missed anything important. A juicy post to get your teeth into before the 18z.- An honest evaluation of the model performance this week. So we are there now ( all but) - but the wide variations between the models have been removed & finally we have some unity with the best of it seemingly here at T84. http://www.meteociel.fr/modeles/jma/runs/2013120212/JN84-21.GIF?02-12 http://www.meteociel.fr/modeles/jma/runs/2013120212/JN84-7.GIF?02-12 into 96. Within this short window of 18-24 hours there is the prospect of storm force Northerly winds & heavy snow showers packing into Northern Scotland, western Scotland, NI & possibly NE Scotland- Im sure we will see a line of snow showers glancing the extreme east coast- but all staying offshore. Perhaps now we have allignment of sorts - todays a day to reflect on the Rollercoaster that has been the model output of the last few days. ECM- Very very strong consistency from the ECM, showing the Northerly pattern - in-fact the ECM has had the correct pattern type on Nov 26 @ 00z & 12z - but really got its act together on the 27th- Here are the ECMs for the last 5 days running 216 - 192 - 168 - 144 - 120 00z + 12z 216 chart 27th http://www.meteociel.fr/modeles/ecmwf/archives/2013112700/ECH1-216.GIF?00 SPOT ON http://www.meteociel.fr/modeles/ecmwf/archives/2013112712/ECH1-240.GIF?12 VERY GOOD 00z + 12z 192 Chart 28th http://www.meteociel.fr/modeles/ecmwf/archives/2013112800/ECH1-192.GIF?00 SPOT ON ( 100 miles to far west though) possibly slightly over amplified http://www.meteociel.fr/modeles/ecmwf/archives/2013112812/ECH1-192.GIF?12 EXCELLENT 00z + 12z 168 Chart 29th http://www.meteociel.fr/modeles/ecmwf/archives/2013112900/ECH1-168.GIF?00 V Close but to amplified at the SW Greenland tip http://www.meteociel.fr/modeles/ecmwf/archives/2013112912/ECH1-168.GIF?12 V Close but to amplified at the SW Greenland tip & to far west. 00z + 12z 144 chart 30th http://www.meteociel.fr/modeles/ecmwf/archives/2013113000/ECH1-144.GIF?00 V Close but as above- slightly to amplified & to far west 200 Miles. http://www.meteociel.fr/modeles/ecmwf/archives/2013113012/ECH1-144.GIF?12 V Close but eastward correction 100 miles - still to amplified. 00z + 12z 120 01st http://www.meteociel.fr/modeles/ecmwf/archives/2013120100/ECH1-120.GIF?00 Spot on barring the over amplification http://www.meteociel.fr/modeles/ecmwf/archives/2013120112/ECH1-120.GIF?12 Correction East, angle of amplification more NE instead of North- Looks to be spot on. 00z + 12z 96 2nd today http://www.meteociel.fr/modeles/ecmwf/archives/2013120200/ECH1-96.GIF?00 SPOT ON http://www.meteociel.fr/modeles/ecmwf/archives/2013120212/ECH1-96.GIF?12 12 hours later spot on.... ECM Summary : If you look at the GLOBAL Picture- back across the last 12 runs you will see it nailed it on the 26th - some 9 days out at 216.- that's the ridge in the Atlantic, Deep low digging south over the North sea, Aleutian Ridge moving SE downstream & a split flow over the states with a low in the Midwest. The ONLY area of fault on the NEW updated ECM has come from the area around the SW tip of Greenland & the speed of the solution- being slow & amplified, in-fact its not 'quite' been there & that subsequent swing to a faster solution has taken the amplification past the point when it no longer goes North, but ENE traversing the coast of southern Greenland. HERE What we are talking is an UNDER estimation of the Jet by a maybe a FEW M/S - The net correction is a 'slightly flatter pattern, a slightly eastward jog (200 miles is nothing in weather terms- but Massive for the UK) & of course 1 full less day of cold as there is no high pressure to traverse around the high but through it. We need to be clear though the ECM has never promised sustained HLB, just over amplified the ridge towards Greenland. Incidentally the ECM made a similar mistake the other week, that is- totally lick the GFS in the overall pattern but mistake the over amplification- which again has big repercussions for the UK- this was the model output ECM http://www.meteociel.fr/modeles/ecmwf/archives/2013111412/ECH1-144.GIF?12 Notice ridging into Greenland ACTUAL Varification: http://www.meteociel.fr/modeles/ecmwf/archives/2013112312/ECH1-48.GIF?12 - Notice the flatter upstream pattern- right in the place it hurts for us. What to take away from the ECM for the rest of Winter, ECM is the leading model over the GFS, it licked the 500 MB pattern 9 days in advance & has stuck with it run after run all the way through, however around the Iceland region it 'sees' more ridging than perhaps is going to happen- there's not many places in the globe that the extra amplification matters, however at the southern tip of Greenland there comes a cut off where systems all of sudden STOP going North & suddenly start going East- this through an angle of 90 degrees.- so a SMALL error / bias which would normally swing from say 10 degrees to a ever so slightly flatter 20 degrees to the North is suddenly swung from 0 degrees North to nearly 90 degrees East. This pattern change has a direct impact on the sustainability on UK cold as it shortens the cold & reduces the westerly penetration of cold- This small error is some peoples eyes is a huge error- hence the calls for the ECM being trounced / its failed its followed the GFS etc etc- No the model error is small but the visible impact to the UK is huge.- so the perception is skewed towards a thought process that the model is rubbish. Its not- its king with a bias just like nearly all the models. In terms of the rest of the Winter wit the ECM I will generally STILL run with this model - why? because the Hemispheric pattern for the last 4 years has been heavily loaded towards Northern blocking so fortunately the ECM bias hasn't been visible due the conditions actually supporting the bias, however this winter thus far that bias has made it look a little foolish - when actually its performed superb. So for Future budding cold spells look towards Southern Greenland to see if there is any low pressure or shortwave action that is the key trigger - as this may be to slow & to far west in the ECMS eyes- then as it corrects east the low slips east of the tip rather than South. SW GREENLAND = CRUCIAL TO THE UK COLD. The GFS model... ( Links are the 12z & 00z model only) What can I say about the GFS ..... well in the name of balance when the ECM at 216 was picking up the pattern for spot on the GFS was here- 216 00z & 12z http://modeles.meteociel.fr/modeles/gfs/archives/gfsnh-2013112700-0-216.png?0 Very good but to flat with the US pattern http://modeles.meteociel.fr/modeles/gfs/archives/gfsnh-2013112712-0-216.png?12 VERY GOOD 192 00z & 12z http://modeles.meteociel.fr/modeles/gfs/archives/gfsnh-2013112800-0-192.png?0 Pretty good but upstream Midwest low very fast ejecting out to pole http://modeles.meteociel.fr/modeles/gfs/archives/gfsnh-2013112812-0-192.png?12 AWFUL AWFUL look at the eastward bias in all its glory our northerly it over into Germany 168 00z & 12z http://modeles.meteociel.fr/modeles/gfs/archives/gfsnh-2013112900-0-168.png?0 Not bad- pretty close upstream http://modeles.meteociel.fr/modeles/gfs/archives/gfsnh-2013112912-0-168.png?12 POOR AGAIN- look at that bowling ball low to the NE- but like all the other runs to Greenland ridging 144 00z & 12z http://modeles.meteociel.fr/modeles/gfs/archives/gfsnh-2013113000-0-144.png?0 V Poor but very flat- +4c isotherm across England some 14 degrees to warm @ 850. http://modeles.meteociel.fr/modeles/gfs/archives/gfsnh-2013113012-0-144.png?12 Poor again- to far EAST - England has zero cold air. - Eastward bias evident again. 120 00z & 12z http://modeles.meteociel.fr/modeles/gfs/archives/gfsnh-2013120100-0-120.png?0 Pretty good ticks all the right boxes. http://modeles.meteociel.fr/modeles/gfs/archives/gfsnh-2013120112-0-120.png?12 Slightly to far east again but catching up & westward correcting. 96 00z & 12z http://modeles.meteociel.fr/modeles/gfs/archives/gfsnh-2013120200-0-96.png?0 SPOT ON http://modeles.meteociel.fr/modeles/gfs/archives/gfsnh-2013120212-0-90.png?12 SPOT ON. GFS SUMMARY Why do I personally Hate the GFS- because its always playing catch up to the EUROS, Its always flat when the Euros show an amplified pattern so is wrong nearly every time we get a Scandi or Greenland high. We get 4 runs a day- which If I overlaid all the other 12 runs would show a multitude of scenarios, some at the extreme eastern end of the range, some over amplified ( looks like the 18z is usually the pub run) & some just on some wild tangent- usually the 06z. Should I dismiss it- well I'm going to change my tact on GFS, what the faster flat pattern helps to show is usually the opposite of the pendulum, If the ECM is at the slowest amplified end then you can bet your bottom dollar that the GFS will be the flattest, with this in mind quite often the final solution is a blend of each- the halfway house- but normally not quite halfway to the GFS, more like 1 third to the GFS & 2 thirds of the EUROS- From this you could generate a predicted forecast, but with one very difficult element & that is does the 2 third house create any pinch points that could change the final pattern so drastically for the UK- 2 main areas arise from this- ( For UK cold)- Southern tip of Greenland energy is 1 & the other is when we are setting up Easterlies & low pressures are projected to move south then SW whilst the ridge builds above.- The fast solution ( GFS ) will throw the low pressure further into Europe - but the bigger impact on the long-wave pattern is instead of a Scandi High you see a 'Sceuro' high, with the UK in a southerly or SE flow & the jet to flat on top. Then as the Easterly approaches its how far does the GFS move to ECM where the Sceuro is suddenly a Scandi high again because the solution was in-fact slower. This example is VERY evident tonight. GFS SCEURO HIGH- http://modeles.meteociel.fr/modeles/gfs/runs/2013120212/gfsnh-0-192.png?12 JMA Scandi high -http://www.meteociel.fr/modeles/jma/runs/2013120212/JN192-21.GIF?02-12 This all comes from FAST v SLOW solutions. Anyway, what to take away from the GFS- 12z Eastward bias. IGNORE- if its significantly FLATTER or EAST than the ECM. 6z/18z . IGNORE - if its significantly different to the ECM. 00z- do not discount- I cannot find to many faults with the 00z GFS- not biased in many ways & generally the most consistent. What we can also take away is the GFS will find the weaknesses in the blocking first ( usually) because its primed for a faster solution- so that can support us going forward with comparisons with the ECM. The model that's come out best again is the UKMO- resilient & Smooth, seemless & minimal fuss. In this case it started at 144 with the 2 thirds house & has never changed since. The Scandi High.......... I'm pleased that I presented this idea first ( even Mr Holmes questioned the 500 heights not following ANY ridging to Scandi) The forecast was driven by the angle of the jet coming out of Canada & the subsequent split flow- It is now appearing in the models- So what would be tonights forecast- based on the ABOVE model inconsistencies. GFS- 12z 240- Slight amplification - http://modeles.meteociel.fr/modeles/gfs/runs/2013120212/gfsnh-0-240.png?12 But a Euro high- Mild SW winds for the UK. ECM 240 12z Much better amplification http://www.meteociel.fr/modeles/ecmwf/runs/2013120212/ECH1-240.GIF?02-0 KEEN ESE wind & very cold at the surface, - JMA 192- Run of the day http://www.meteociel.fr/modeles/jma/runs/2013120212/JN192-21.GIF?02-12 Easterly @ 216 GEM 240 - AWSOME http://modeles.meteociel.fr/modeles/gem/runs/2013120212/gemnh-0-240.png?12 But... the Best suite of the day is the ECM 15 day. 00z Chilly http://www.knmi.nl/library/php/resample_image.php?filename=/exp/pluim/Data/pluim_06260_0_00_60.png&width=692 day 11/12 mean around 4c. 12z very much colder http://www.knmi.nl/library/php/resample_image.php?filename=/exp/pluim/Data/pluim_06260_0_12_60.png&width=692 ( swop to 12z) Day 11/12 mean now down to 2.5c & the control + op very cold. Therefor the updated forecast based apon the model bias today is- Northerly toppler, for 24 hours, high pressure ridging over the top but contrary to the GFS no WAA getting into the UK barring the extreme NW - The SE staying cold- day 8 -9 look for Energy dropping south into scandi in the form of a shallow low- with rapid pressure building NE, the UK sitting at the extreme western end of blocking for day 9/10.- light Southerly or SE tug. Then energy getting underneath tugging the winds easterly & increasing day 12. Look out for the Maps for 13/14 December. best regards Steve
  5. 114 points
    Early guidance forewarning of next weeks weather was issued earlier on, and this has been further enhanced with extended outlooks in bulletins. AFAIK (comms not being my area) public agencies and major private infrastructure will begin a daily briefing cycle as of tomorrow. To revisit previous post, latest MR output (MOG) resolving to further mute ‘breakdown’ scenario; with continental blocking signal reinforcing through well into March. Atlantic incursions are expected with southerly deflection; considerable potential for extensive and disruptive snowfall as these air masses interact. Short term, ECM:UKMO evolution favoured and considered likeliest; corresponds well with other products and illustrates fair consistency. Small ramp. Next week = mega. SB
  6. 114 points
    Evening All Ice Cold hope your still with us .... So the much touted SSW is coming into view & here’s my thoughts + timelines of when / where to expect it... We have seen lots of posts & comments on it - but whats the reality likely to be -??? The Omni present warming in the GFS charts is usually due to the model & its poorer vertical resolution V the ECM, as a result there is an over reaction / over estimation of how much a warming is going to impact the zonal wind @10MB - so because of this 'bias' when viewing the mid / long term outputs churned out by the GFS we have to be a little on the sceptical side as these are normally moderated & scaled down even wiped out ! However we have now seen the evidence in the Berlin site that a downwelling SSW event will make it to the 10MB level & indeed go on to challenge the date record for the time lf year- ( this is NOT the same as the usual deceleration of the zonal wind we see at this time of year as that is more of a gentle reduction all the way to mid april when the vortex breaks its annual westerly influence ) So as highlighted we have passed the point of no return in the stratospheric modelling where a SSW is now just 5 days away for the 12th Feb *** Take note of this date -- The plots below show steep downward curve of a signature warming Note the main black line being Climo - but the ensemble mean from the GFS running out at mid -20 to -30 M/S... The clustering is quite close - further backed up by the another illustration of the ensembles from the hannah attard site With the mean bottoming out at -32M/S *The date record for this time is ~ -17 M/S & the all time record low ( using Merra data ) is -35 M/S The ECM berlin forecast below is not as bullish as the GFS coming out around -17 M/S @10MB but none the less still classed as significant event... So what we have in modelling terms of a SSW due is * The first one in 9 years ( I dont think last year was classed without checking ) * Possible record breaking reversal of tge zonal wind... If your thinking whats best in terms of impacting the UK its simple- The lower the negative number the better... - record breaker ? yeah I will take that please... Why?... The bigger the negative number the stronger the easterly flow is across the mid lattitudes. !! ( think feb 63 / jan 85 & so on ) Whats the models churning out then? The SSWs are classed as 2 types - Wave 1 displaced vortex or - Wave 2 Split Vortex .. This is whats expected - A classic wave 2 Split vortex- with 2 clear areas of poleward flux - over the far East & canada- Now luckily for me the historic SSWs have already been classified -we are looking for la nina years / W2 / split vortex- 6 years appear as matches - 28 Jan 1963 - 7 Jan 1968 - 18 Jan 1971 - 1 Jan 1985 - 21 Feb 1989 - 24 Jan 2009 Below are the 10MB increase in temps at the time when the zonal wind hits 0M/S Obviously they all have 1 thing in common- The huge rise in temps across the pole - Now the Date of the zonal Mean hitting 0M/S isnt the day of peak blocking - Looking at the dates above peak blocking appeared 7 - 11 days post Reversal - see below day 11 charts from the above warmings ( 500 MB anomaly ) Whats apparent is HLB is quite prevelent & most are centered ( for us ) around greenland & Western Scandi - Also all 6 Splits have varying levels of troughing to the south - but all have an anomaly- So that really leaves with a level of expectation that should at least give us some confidence for Feb over the following dates- 12 Febuary : is 'R' Day- as in the reversal of the 10MB zonal wind where the eastward progessional component is replaced by a westward one 13/14 Febuary : is peak 'R' days where we will know the magnitude of the warming & just how much westward ( reversal ) component there is - Sub -20 M/S is the date records & anything below is the jackpot - 16-18 Febuary - Mid to high lattitude transitioning - This is where depending on how lucky we are for our area we will see MLBs start migrating North to the pole as zonal wind lag filters through the lower layers of the atmosphere & support builds for HLB - look for the 3 key wave patterns ( atlantic / Scandi & pacific (-EPO) The UK can get very cold in this period if the migrating highs are favourably positioned from the outset.... 20-24 Feb - Peak HLB blocking across the NH - peak -AO signature & peak cold overall for the mid lattitudes ... *** IF the GFS lands with the depth of negativity then Late Feb early march will be on a par with 2013 for AO negativity & possible / probable UK cold / snow.... if the negativity is watered down then the cold signature will be watered down & less dominent in western Europe... Best S
  7. 113 points
    Come on those looking for the breadown before the major cold and snow has begun You will be very lucky if that is the correct word to see this in ANY winter in the rest of your lives I would suggest, let alone the end of official winter into the first week of spring. I worked through 1962-63 and was 8 years old in 1947, so having looked at GFS output over the last several days and UK Met along with ECMWF I am close to being gobsmacked at how the deep cold has been correctly forecast on the models from 2 weeks out. Equally congratulations to those of you who understanding the SSW and other connections far more than me were predicting cold even further back. Looking at the 12z GFS, not too different to other runs over the past -3 days for my small area, and it predicts 2 ice days, snow on 3 or 4 days with possible depths greater than anything here since 30 November into 1 December 2010. As a long since dead football commentator was fond of saying, 'quite remarkable'. I am now going to see if I can discover, during the 1962-63 coldest spells if the history is available to show what 850 mb temperatures were. I know what the surface temperature were, and have several times posted that when folk reminisce about past winters. Enjoy but please do remember to try and support anyone living near you that may need this, this is a going to be a pretty severe test for a lot of folk, even if their heating is up to it and they can afford it.
  8. 112 points
    So a rather long post ( Will also clip into the winter forecast thread ) However just an update on saturdays post, a large debate around models - & I took the day 6 UKMO & GFS charts to compare for verification- These were both of the 6 dayers GFS on the left. Note GFS flat with no heights in Greenland, UKMO more amplified with heights - Also a circular vortex North of Scandi. UKMO has energy seperation & a closed low - GFS just sends a 'block' of energy through - Look at todays UKMO 72- Comments: -Circular vortex just North of Scandi -Closed low traversing East towards Iceland - Residual heights over Southern Greenland - Arctic High 1040MB. Conclusion UKMO is a clear resounding winner here- every element that differentiated from the GFS is still apparent in the T72 chart, this is a big thumbs up for the UKMO, proof ( on this occasion ) that the GFS clearly has an eastward bias & why looking at developing heights over the pole ( NB UKMO 144 today ) The UKMO resolves energy better... So, onto the SSW it seems an eternity since the first warming started showing up way back in December - but now we are day +6 since the wind reversal- Much of the discussion has been about the 'slow' response in terms of downwelling in terms of creating a significant AO - This is depicted nicely on the NAM index which I have saved from the other week- The GFS bias initially showed minimal downwelling, however gradually ( like the comparison with the UKMO above ) has slowly come into line with a more 'propergating' feature. I think we have been unlucky with the QTR - sadly the NOAA composites page isnt available, however twice there has been significant mid lattitude blocking developing in the locale forecast as a QTR relating to the strat split- However the blocking has been just to far East for us to really gain any benefit - *but* as far as Europe as a whole is concerned in terms of snow this winter could challenge the record books in terms of sustained depth from mid Jan onwards- My memory ( from the old teletext days ) was that St Anton could reach 600CM on the tops by the end of Winter- By the end of this week it will be North of 400CM Also records going in Greece with snow in Athens & -23c reported North of the region- So whilst the QTR missed us that release of deep cold didnt miss everyone... The next stage of this SSW / Split will be crucial for winter as the norm here would be a gentle recovery from the PV ( not to normal strength ) - however if like me you were hoping for something that lasts longer than a few days - IE 1 MONTH then a secondary warming & further splits would be the upper cut to the PV that would knock it out for the rest of the Winter. However just before commenting on that lets see the progression of the downwelling- The charts at the top are from around NYear- now look at the NAM index from the GFS today ( remember its still not the best model for coupling the Strat > Trop ) Here is the NY 100HPA profile V todays Lots more clustering below 5M/S- some below zero. This is why we are seeing the GEFS respond post 192 - Note the AO Ensembles - Starting to gain momentum towards -4. Moving through day 9 on the ECM strat from yesterday we see that the Uwind is still negative but importantly the allignment of the vortex lobes are significantly different to this week - encouraging blocking- Red is the left lobe allignment Blue is the right lobe allignment Yellow is the blocking potential- Its quite apparent that despite a split the current shape of the lobes means that the U wind off the states doesnt support blocking, but day 9 ( alligned to the trop response ) allows for a different pattern that is complimentary towards the jet being sheared up the western side of Greenland & also residual flow alligned SE in the atlantic - We should also see the vortex 'throwing' Scandi Deep cold SW across Europe - This is the jet flow -( yellow ) & associated areas of deep cold. This is a solid -AO / + PNA / -NAO pattern. This is why the models have suddenly flipped to that sharp NW > SE allignment If you are looking for sustained cold then a SSW split + follow up warmings & continual negative zonal winds are the hallmarks of LONG cold spells, * with the usual caveat that we are the SW point of the cold & could always see some milder air pushing back west * This could be a crippling final quarter of Winter for Europe & the Balkans- Best S
  9. 107 points
    Short answer The short answer to your question is yes, the presence of low pressure (at higher altitudes, being coincident with very cold upper air), makes the air more unstable, as the gradient in temperature between the surface and higher altitudes becomes larger. Long answer The long answer requires some explanation on stability. To avoid things from getting too complex, I will not go into detail about Skew-T diagrams. (If one wishes to have an explanation via Skew-T charts, just ask ) Stability of the atmosphere (Un)stability has to do with the 'tendency' of a parcel of air to rise from a certain position (in altitude) or to stay at the same position. This tendency is related to the temperature a parcel has compared to its environment. Imagine a parcel starts to rise from a certain altitude (say, 1000 meters). The parcel then cools adiabatically (meaning it does not 'mix' with its environment) up to a certain height. If a parcel then finds itself being cooler than its environment (stable conditions), it will drop back to its original position (remember that a certain volume of cold air is in general heavier than an equal volume of warm air). However, if the parcel is warmer than its surroundings (unstable conditions), it will continue to lift to even higher altitudes until it reaches a height when the parcel becomes saturated. This height is the height where clouds start to form. Thereafter, the parcel will still continue to rise up to where it finds itself in an environment that is warmer than the parcel itself. (Note that the cooling process during ascent of a parcel is different when the parcel is saturated, but goes too far to treat this in detail). The parcel then stabilizes, and this can (under great simplifications) indicate the height of a cloud. What this comes down to is that when the air is unstable, showers are easier to form based on the parcel analogy described above. A good measure of stability is the change of temperature with height. If the temperature drops sharply with height, the atmosphere can be considered unstable (referring back to the parcel analogy). When the temperatures decreases only weakly with height or even increases with height, the atmosphere is stable (from the parcel analogy: a parcel will find itself colder than its environment after ascent, meaning it will drop back to its original position). To illustrate this, below is a series of images showing the parcel analogy: Stable situation Unstable situation In the images above, the x-axis indicates the temperature, while the vertical axis (y-axis) denotes height. For both graphs, the red line indicates the change in temperature over height of the environment of a certain parcel (technically spoken: lapse rate). Note that the environmental temperature drops much more with height in the unstable situation than in the stable situation. The black dot indicates a parcel on a random level. The arrow pointing to the upper-left stands for the adiabatic rising (and the accompanied cooling) of this parcel. For both images, this parcel cools at a same rate (so the black arrow has the same slope to the left on both images). As can be seen in the stable situation, the parcel becomes colder than its environment after rising. Therefore, it is being forced downward again. On the other hand, in the unstable situation, the parcel becomes warmer (and thus lighter) than its environment, indicating the parcel will continue to rise. Temperature difference representation between surface and aloft Coupling the part given above back to the presence of low pressure at higher heights and stability, one can realize that the difference in temperature between the surface and aloft (I'll be using the 500 hPa level, being about 6 km, as a reference for now) must be very large in order to have an unstable atmosphere. If the atmosphere can be more or less unstable when the temperature at the surface stays the same, the temperature at 500 hPa has to vary accordingly. In other words, changes in stability can be explained by variations in temperature at 500 hPa level. Simplifying a bit, one can assume as a general rule that low pressure activity at higher altitudes is accompanied by lower temperatures at that same level. (more in-depth explanation can be found here). This means that, in general, low pressure at higher altitudes indicates the atmosphere is more unstable than when high pressure is present at higher altitudes (and thus showers are by approximation more likely to form when low pressure is present at higher altitudes) Seasonality in stability An important difference between summer and winter regarding stability is that the surface is usually colder during winter than summer. This means that the upper air has to be colder in winter to acquire instability than during summer. Combing to current weather The weather that we are about to observe this Thursday up to the weekend is a very nice example to illustrate the relation between stability and the presence of low pressure at higher altitudes. Therefore, given below is the pressure forecast of the GFS for next Thursday: GFS surface level pressure and 500 hPa heights (colours), 18Z T+48 It is important to focus solely on the 500 hPa heights, indicated by colours. As a rough guide, purple/blue colours indicate low heights (lower pressure activity at 500 hPa height) while yellow/red colours indicate high heights (high pressure presence at 500 hPa height). Note that there is a very deep trough (low pressure area) present at 500 hPa height over Western Scandinavia and Northeastern UK. Referring to the explanations, low pressure at 500 hPa should coincide with lower 500 hPa temperatures. Much higher heights (relatively higher pressure) are present to the southwest, west and north of the UK. Therefore, the 500 hPa temperatures for the same timeframe (from the GFS forecast) are given below: GFS 500 hPa temperatures, 12Z T+54 The runs of the GFS are two different ones (18Z above, 12Z below), but they are valid for the same timeframe. Since big changes between runs for 2 days out are not likely, I'll therefore assume that both runs show the same situation. Note that there is a large swathe of very cold 500 hPa temperatures present to the east of the UK (down to -38*C). This is associated with the very deep trough present to the east and over the UK. Much warmer 500 hPa temperatures can be found to the south and west of the UK, while the 500 hPa temps are also slightly warmer to the north of the UK. The surface temperatures do not vary much in the neighbourhood of the UK at this timeframe (except for land/sea effects). The surface temperature chart for this Thursday can be found here. Thinking of the parcel analogy given in the beginning of this post, it becomes evident that showers are more likely to develop over or to the east of the UK than to the north, west or south (assuming equal surface temperatures). Northerlies and stability Regarding wind, there are northerlies present over and to the north of the UK, while to the east of the UK there is barely any wind. (you can find the wind forecast from the GFS here). However, as we can see above, the air to the north of the UK is less cold than over the UK itself. This means that despite the fact that the northerlies are stronger to the north of the UK are stronger than the ones over the UK, the air over the UK is more unstable (due to the lower upper temperatures). Exceptions One possible exception is the presence of a polar low. Such systems may pop up out of nowhere and yield a lot of snow, being completely overlooked by global models. Quoting from s4lancia: Summary To summarize the relationship: low pressure at high heights is coincident with cold upper air, yielding a bigger temperature difference between the surface and aloft. This yields a more unstable atmosphere. It has to be kept in mind, though, that this relationship is simplified, so it does not have to match the actual conditions in any case. Conclusion Even a very short question can have a very long answer, and in fact there was much more that possibly could have been told about this. I hope this answers you question sufficiently . If something is not clear, do not hesitate to ask! Furthermore, I am by no means an expert on this subject, so any additions/corrections are also very welcome! Finally, if one would like some explanation about this via Skew-T diagrams, that's possible (probably with some delay ). A good read about Skew-T diagrams, which could also serve to visualize stability, is given below: https://forum.netweather.tv/topic/16002-a-simple-guide-to-understanding-skew-t-diagrams/ EDIT: Added graphical representation of stability. Sources: http://www.wetterzentrale.de/topkarten/fsavneur.html http://www.keesfloor.nl/weerkunde/10neerslag/10neerslag.htm https://forum.netweather.tv/topic/27989-how-to-try-and-forecast-snow/ https://forum.netweather.tv/topic/16002-a-simple-guide-to-understanding-skew-t-diagrams/ http://www.weatheronline.co.uk/cgi-bin/expertcharts?LANG=en&MENU=0000000000&CONT=ukuk&MODELL=gfs&MODELLTYP=1&BASE=-&VAR=z500&HH=48&ZOOM=0&ARCHIV=0&RES=0&WMO=&PERIOD=
  10. 107 points
    Right, I am going to try and calm things down a little in here, as well as answer a few questions that I have seen along the way hopefully. The over-riding message from this post is this - Calm Down! We approach November with two things which are a recipe for over-excitement, mood swings and plenty of toy throwing. These two ingredients happen to be: - Something that can barely be described as a 'Winter' from last year - A Polar Vortex this year more absent than UKIP at Notting Hill carnival So, let me start by addressing the misery of last year. I have seen some occasional posts asking whether what we are seeing right now is 'normal', both in this and other threads. My assumption is that by normal, they mean preceding a mild winter. Below are some mid-November charts from what we might consider to be some of the milder years of recent times: A very random assortment and chosen for a very specific reason. Whilst not all of them feature hugely organised vortex's necessarily (and that in itself becomes a point - just because right now there is little organisation to the vortex does not mean it can't still become more organised and vulgar) they all lack a crucial ingredient in something we now know, thank's to Cohen, is a crucial ingredient in SOME colder winters, and something you may be sick and tired of hearing about by the end of November - The Scandinavian High/Aleutian Low combination. For example, here are some of the colder winters of recent times: Notice in all of these years we end up with a Scandinavian High and Aleutian Low combination during November. Now this is not me saying that before every cold winter we have to have this setup, but in the majority of years we have seen this setup occur it has lead in to a colder winter. This is all linked in to Cohen's research on the Snow Advance Index, with the rapid snow advancement (and interactions thereafter given the rapid cooling of the surface) giving us the stronger than usual Siberian, and eventually (hopefully) Scandi/Sceuro ridge. If we have a look at the forecast setup for the middle of November this year: We see something fairly similar forecast. I think this serves as an important point heading forward for those of you impatient to get the cold in as soon as possible. The best case in point for this is the now infamous December 2012 failed Easterly - the whole idea here was that yes as nice as it would have been to get the cold in as soon as possible, it was not vital that we got the early season cold. It was once again then a Scandinavian high that initially looked to retrogress to advect the bitterly cold air across Europe Westwards in early December, before some more shortwave drama lead to record sales of Nick Sussex's prozac. But the point is, we had the Scandinavian high/Aleutian Low combination at this time, which helped to drive wave activity in to the Stratosphere and ultimately led to the cold JFM 2013 period which we saw. One final addition to make before we take a look at current forecasts, here was my analogue for this November, based around OPI, eQBO and El Nino matches: Notice a few key things which this picks out which we already know to be true: - Trough to the West of the UK - Aleutian Low - Scandinavian Heights - The cold pattern across the USA with a West Coast ridge and East Coast Trough. If you try and match that to the 8-10 day height comparisons posted above, you'll notice a pretty good match overall with just a few minor tweaks. Roll that forward in to the winter months and you get this: So, the overriding message I have for you all is this: Whilst we are seeing some wonderful synoptics on show which at least makes a nice change from last year, it really is not imperative that we get the cold in this early. Even the greatest winters of '47 and '63 did not get going until after Christmas, hang tight and try not to get aboard the rollercoaster too early. Get outside, head down to the pub, go see some friends and family etc. because we all know that once the truly cold charts start showing none of us on here are going to have any sort of life outside of the area between our laptops and our lamp-posts. So, back to the future... If we keep the above in mind and search just for the Scandi High/Aleutian Low combination for now: We can generally still find that combination in the outputs through to around day 10, and if you want to make it easier to spot this, try using the anomaly charts instead: ECM Ens. Day 5: Day 10: And if you head over to the stratosphere thread and take a look at some of the posts from this morning, you will see some wave activity starting to rear its head once again, which is most welcome. So as we are only 5 short days in to November, this is all I will be looking realistically for now, the Scandi High/Aleutian Low combo, and anybody expecting anything other than eye candy in the next couple of weeks may be a little misguided. Let's wait until the end of November before we start getting too excited about anything potentially good synoptically, hoping that in the meantime we can start bringing some of that colder air in to Europe. SK
  11. 107 points
    Hi Mucka- certainly a response worth a reply. In the last 3 years we have learnt the hard way that whilst statistics prove that without doubt the ECM is the best model, they also prove that sometimes statistics are meaningless when we look at the fact the UKMO & GFS are on a par @ day 5 for error, what we don't ever see is where the UKMO has its errors ( I believe there is a GFS page that show the model bias errors by run- im sure Lorenzo or Sebastian posted it- but TBH it confirmed what was obvious anyway) Within the last 3 years I don't recall ANY time when a HLB scenario has come to fruition without the UKMO being on board, the most painful one was the high over scandi 2/3 years ago when ECM + GFS were on board & the UKMO just cranked in a shortwave over Denmark at day 6 & that was it game over. The UKMO has gone up in my estimations - so much so I place it as important as the ECM - so I cant ever dismiss the UKMO unless its 'significantly' adverse to pattern expectation. So if you take this morning ( & I NOTE FROSTYS Quote of me from yest) The UKMO & ECM are very similar at 144, we are not looking at the UK Im talking about overall wavelength & profile, however where they differ is the tilt & angle of the troughing up towards Greenland- UKMO POS TILT- http://www.meteociel.fr/ukmo/runs/2013111700/UN144-21.GIF?17-06 ECM NEG TILT- http://www.meteociel.fr/modeles/ecmwf/runs/2013111700/ECH1-144.GIF?17-12 UKMO spells a 'probable' return to something milder, where as the ECM signals continued cold- indeed if you look at the ECM 240 the Artic high is making an appearance- which is in line with the tropospheric lead stratosphere with wave 2 activity higher & no doubt a deceleration in zonal Mean... ANYONE HEARD OF TOTAL ZAPE? - Anyway moving on Its annoying for me 'sometimes' when people start throwing their toys out the pram saying that I have discarded a run- I honesty think they still believe that I just discard runs for the fun of it- like I am going to spend time on here just making things up- I only discard something that I believe is significantly adverse to my expectations taking into consideration the historic performances & frequent model bias. The ECM is the best run in the long run its the most consistent, but it still has its flaws, noticeably the 12z ECM has 'some' history of being over progressive with the jet- then the 00z reverts back to the 'probable' correct pattern- the bonus however with the ECM is it usually corrects quickly as opposed the GFS which will make the same errors over & over again. I didn't need to even look at the 06z this morning as I could have bet all the tea in china it would be a UK high / toppler scenario - as it always is..... whatever the eventual outcome HLB or toppler it will always be useless. Referring back to the ECM/ UKMO I cant discard either run today as a bit like the NOAA hurricane cones of forecasting IE- both models do fit together & with that in mind a small sway in jet angle & energy both models could move to the other one- I would say at the this stage the UKMO will move to the ECM - I don't ever come on here asking or expecting any praise its not a competition, however I would say that I think if you go back over the last 4 years I would say ive made more than a handful of calls in terms of forecasts - sometimes going against ALL the models in favour of blocking & more often than not been correct, & with the GFS probably near on 95% being right it dismissing it waiting for the blocking come & for the model to finally catch up- even now forecasting the time period it will take for it to catch up! Even just last winter- remember this Easterly where the trough split- Actual 15 Jan chart http://modeles.meteociel.fr/modeles/reana/2013/archives-2013-1-15-0-0.png ECM 5 days before http://www.meteociel.fr/modeles/ecmwf/archives/2013011012/ECM1-120.GIF?12 Has the trough sinking nicely UKMO 5 days before http://www.meteociel.fr/ukmo/archives/2013011012/UW120-21.GIF?10-12 SPOT ON GFS 06z 5 days before http://modeles.meteociel.fr/modeles/gfs/archives/gfs-2013011006-0-126.png?6 This chart couldn't be any further away ( UK HIGH theres a surprise) GFS 12z 5 days before http://modeles.meteociel.fr/modeles/gfs/archives/gfs-2013011012-0-126.png?12 A MESS Now the benefit of heinsite- bearing in mind ive seen every winter run of the GFS for the last 13 years ( ~6000 runs) is after a while you understand the model & its faults- Maybe some of the GFS faithful ( im sure they know who they are) will look at the above & realise that its just a shower of ..... I am trying this year & for the next 3-5 to get to grips with the ECMs failings- ive already noted the odd one here there- especially around lows travelling east across the pole & the fact that when they are going to dig south through scandi the ECM is usually to far South East & of course noted above 12z ECM a bit of progressive bias- but not always & nothing like the GFS Also we should consider this.... 'changing paradigms' Since 2008 we have seen a notable shift in the circulation patterns of the NH in winter- someone reanalysed them but lost them so I taken the time to do them for you & for others- There will be 'some' explanation for this around cyclical oscillations & the sun, but perhaps as above we have changed the paradigm. All are DJF long term Mean. 1990- 2008 anomaly 2009-2013 anomaly look at 1990-2008 the anomalies are negative to the long term mean meaning conditions were MORE zonal than the average which is infact predominantly zonal anyway- so possibly 'super or highly zonal' What the third chart shows is a probable change of paradigm for the NH- ( the only thing that doesn't make it concrete is the small sample size - because it could still be considered an anomaly not a change) So with this important change evident we need to factor this into our forecasting.... Im going to word the next bit as I don't want it to be edited. - I mentioned this the other night, when I see Ians posts his thought process is related to the GFS & also his perception of the 'Mo dern winter' which up until 2008 fitted the bill perfectly - why? * Atmosphere predisposed to the zonal express * GFS biases supporting what actually was happening with the model evaluation- IE possibly the EUROS being to amplified & the GFS cranking the jet up- its bias was unwittingly making it more accurate in projected cold spells because its downgrades were more nearer the truth- So now flip it on its head- everything is reversed- so the Mod ern winter has gone- people using Ians method have gone from near 100% success to near 100% failure - ( of course there will be some intervals where the cold projected WILL still fail- that's the nature of beast- look at the second point though- if everything is now reversed then the Euros are not amplified enough & will always play catch up to the 'new Post Mod ern winter'... anyway I hope this helps you & a few others who might not understand my rationale.... its not all make believe people- its sound thinking...... cheers S
  12. 105 points
    If I may interject here... It might be worth you going back and reading the posts that have been made, and represent what was actually said vs what is happening - and not spurious interpretations of words you choose to put into mine, and others mouths please. There have been several reviews. Indeed, the last one I made was barely 48 hrs previously on Wednesday! They are very easy to find on one's activity page. But as you admitted recently - you don't read many posts (beyond trumpeting your own) other than the ones you feel the need to 'challenge' as part of your compulsion for one-upmanship A pattern change from highly +ve AO was muted two weeks back of an Atlantic ridge vs Scandinavian trough (along with my usual 'waffle' of reasoning and explanations) At this time, however, you were customarily oscillating between the highs and lows of intra model day output - and fighting the corner of the Russian High, which never had any support to back westwards a cold pattern. Duly, we have arrived at that scenario of Atlantic ridge and Scandinavian trough - and also an upstream sub tropical jet - a sequence which was anticipated through watching the the expected movements of the Global Wind Oscillation through an extreme high amplitude Phases 5-6-7. They are too long and tedious for you I know, but you could go back and read the posts for yourself. I do believe that is exactly where we are - and what is playing out still in the modelling through this week. I have, for what it is worth, personally stayed clear of all the erratic and incoherent operational output and also taken a distrust to ensemble data in the last day or so, such is the chaotic nature of the pattern - and especially with the bonus addition of a January Atlantic tropical storm thrown into the mix as well! Attraversiamo... Going back to the posts and the reality vs the misrepresentation. I posted about 10 days back as the arrival of the upcoming amplified pattern came into focus that we might look to a loosely based comparison (as difficult as it is to do this in terms of the uniqueness of this 15/16 Nino event) of the Nino forcing that evolved in the Pacific through the 82/83 winter. Not meant to be taken as a literal meaning that the day by day synoptics will replicate identically, because of course they won't, but as a theme to watch. On that basis, and in terms of the way a highly ramped up atmospheric angular momentum framework has been working in tandem with changes over the polar field to a much more destabilised vortex arrangement, and hence making a highly significant difference to the first half of winter - we might see the NH pattern replicate a similar evolution from Jan > Feb 83. Frankly, and with some time also yet to pass, I see no reason whatsoever to dispute that at this time. Especially as many of the longer range tools and seasonal modelling are indeed now pointing to such an amplified pattern occurring as a theme in the remainder of the winter. As the associated feedbacks that have created these grow, the chances of link-up to the heights over the NE increase - and here parallels with Feb 83 increase further as those charts from the first/second week of Feb imply in the archives Stewart clearly had this analogue in mind himself ( and as part of his obviously more experienced thinking than mine) gave his own very similar rationale behind the tropical and extra tropical forcings that were moving the pattern onwards and he suggested the template from the 17th Jan to approx (I think from memory) 8th Feb for continued development of the theme of change away from the anomalously warm +ve AO theme of the first half of the winter to one that features recurrence of the very theme we see now of amplified Atlantic ridge and Scandi trough. But - with time, this embedding in place in such a way as to increase the likelihood of the southern stream undercutting and backing the cold air to out N and NE further and further towards us the more time moved on. If you look further up this page, I do believe Stewart has updated his thoughts to suggest exactly this development , and further to a post he also made on Wednesday. There is no clearly requirement for me to add further to that latest post, as based on following many same data sources I inevitably come to conclusions that concur. There are many highly informative and knowledgeable people to learn from on this forum - and in addition to those various members, I will happily and freely admit I have attempted to learn from studying and interpreting in NWP model output the same GSDM framework Stewart has been an expert on for so long. People are free to disagree with these methods, and whilst none of us can control the weather and claim to have unique powers of perception to oversee every development, over the course of the last 18 months I have come to fully value the worth of intra seasonal and sub seasonal phenomena in providing insight into how NWP modelling may evolve. Last winter, for me was a great starting point to put these into practice - and which I found hugely rewarding. I would much rather follow such a constructive method of research and learning, and making mistakes along the way as means of improvement, than seeking to undermine others as some bogus means to earn an imaginary competitive forecasting prize at the end of it. That is not the same as having different opinions and respectfully discussing them
  13. 103 points
    Evening Guys Officially signing off for the winter from my window - still all but 5 inches on the ground - have a great year ! Current favourite See you next year S
  14. 103 points
    Reasons to keep perspective: 1) In real time modelling we are right here, right now, turning a massive corner from the blowtorch/rainfest regime of the late autumn and early winter. We have seen the worst of the 90's +AO Nino regime, as referred to in early season posts, and are now staring at the barrel of a 60's to 80's type -AO Nino pattern. Lorenzo, in his own way, discussed the sheer scale of all this in his overnight post - and it really cannot be over emphasised. On that basis, as a weather and weather pattern enthusiast, despite the unpalatable weather at the surface witnessed up to this change, the lead up since summer 2015 into the early part of this winter has been the most rewarding study/observation possible. 2) We can trust that this fervently primed atmospheric circulation, as a seasonal dog of two heads, is set to show what its -AO alter ego can do. In this respect some patience is required while the NAO mode completes a transition to fully connect with the change of regime over the pole. Its not quite there yet. Trust the seasonal wavelengths here the more we head through the month to February, and especially trust what is happening, and is set to further happen, upstream in the Pacific and 'elsewhere' (other posts have covered detail, no further repetition required). 3) We knew before the NWP modelling really ratcheted up a gear through yesterday in terms of the tanking polar and amplified Atlantic profile that another sub tropical jet streak was in the offing circa the 10 day period. And, being early in the overall Annular Modal transition as described here, and in recent posts ( and with some 'latent heat' left especially in the surrounding seas) that an initial tendency towards a west based NAO regime (as the first part of modal transition) might suggest some initial cut-off cold advection scenarios where residual troughing phases with the upcoming jet streak out of the SE USA. However, we cannot be sure yet to what extent, if much at all, this might delay cold air advection fully south. Tbh though, with the trend being a friend, none of this actually matters to me at all at the moment. I'm not absorbing myself too much in intra output details. We are all free to approach the model output in any way we choose of course. I am simply suggesting not to be too unduly ph(azed) and fret over it. 4) Right now, as written yesterday, I think we are seeing the first stage of a lock down (in terms of the change of pattern) that will evolve a new cold regime potentially becoming colder still as we head towards and especially into Feb (in terms of a further cold spell then). Each new daily set of data is re-enforcing this in my mind. Taking the situation in the here and now, and what it is to come - there is more poleward amplification in the circulatory system to shake a stick at. With the polar field drastically changing, we must keep remembering this and have some trust in it. 5) Most all our main cold spells are interspersed with less cold blips - this applied most recently in Dec/Jan 10 (in the south) and also there was a pause during the exceptional late November/December 10 spell. But going back through weather history the list is endless anyway. This is the UK and not Siberia or Northern Canada. In this sense go back to the first item on the perspective list. and see where we have starting to move away from. I've been enjoying the atmosphere tug of war immensely anyway, and then as a adoring fan of snow, like many of us, am trusting in the pattern that is unfolding, I feel I can afford to wait till it arrives outside my window because anticipation is growing for next 6 weeks. The weather will have the final say of course, but I am happy to be very glass full at this time @BFTP : I think that there are good reasons, as outlined in recent posts, for a further cold period in February, and, with less issue regarding any possible west based -ve NAO, and H500 anomalies adjusted slightly further east, quite likely would be colder still than the upcoming one. 'Lock down' is intended to refer to an overall regime change from the first half of winter, not necessarily literally a whole month in the freezer! No-one can predict anything like that
  15. 102 points
    I assume the overnight ECM has (temporarily at least) put an end to the glass half empty stuff from some posters yesterday. I'm sure the next variation in op run will bring them back out - but if you are on here to learn and are hunting snow/cold (sad to see that thread go....) then here's a bit of learning for you. The overnight chart from ECM at the later stages of medium range reliability is fabulous. What you are looking for here is the source of the air in situ over the UK - and the angle of approach from the system in coming...and where it will pull its air from. Note here at 216 you have a generally slack E/SE flow over the UK established from the back end of the week to come, with air being drawn to us broadly from Scandy and Northern Europe - already both snowbound and across a north sea that is not especially warm. Meanwhile the incoming low has purples in it in terms of pressure - meaning it has been drawn directly from the deep vortex low over Canada. As it approaches and disrupts against the higher pressure ahead of it - it "slides" southwards and the winds from that system turn to the SE, pulling dry continental air up from France. The final image shows how the moist, atlantic air (still pretty damned cold because of its Canadian origins) has dropped into France. Eastern UK has a feed straight from central Europe - western parts of the UK from a slightly milder France - but the combination is such (especially in January) that snow is likely countrywide. This is a "slider" low - precisely because the atlantic system has come from the NW and literally slid down the face of higher pressure ahead of it. Are there historical parallels? 3 from my memory that show a variety of similar events. The most similar to the one progged here would be Feb 1996 where we had a very similar setup a couple of weeks later in the season. Note again the deep origins of the sliding system (purples) and the cold air in situ from a SE feed. 1996 brought huge snowfalls to some parts - myself fortunately included this time around while in Dorset. Slightly different, but no less impactive in terms of snow, would be 1985 and 1979. 1979 first. Note here that the incoming system is a lot flatter - it's approaching from due west and meeting the trough in place over scandy. On this occcasion the deeper cold was in the resident scandy lobe and less in the approaching system. Note the isobars ahead of the atlantic system turn, once again, to that SE flow and as the higher pressure ot the south drew away plenty of snow fell. Feb 1979 was full of such events - they kept repeating over and over giving blizzards to all parts. This image below, again not a million miles away from where we are heading but with a very convenient wedge of higher pressure just to the north of the UK - brought some of the heaviest snow falls in the last few decades, especially a few days later around Valentine's Day. And last of all 1985. A bit different this one - but if you are wanting to learn about snow giving conditions good to dig out. This time the system approaching from the west runs up against a block that is much more entrenched to our NE - but the effect really is the same. Moist air from the west disrupts against the colder, denser air in a block ahead of it and slides underneath. Because of the angle of trajectory these are sometimes described as channel lows because the atlantic system's slide angle takes it through northern France as it pulls continental air up ahead of it into its moist lead edge, turning all that moisture to snow. Bottom line is - we are approaching a pattern which could replicate any or all of these situations because of the forcings which are in operation. However - and it is a big however - for every one of these big snow makers there are plenty of historical near misses......either because too much warm air gets wrapped into the system or because pressure to the south remains too high and continues to feed warmth up from the south. Putting my own neck on the block here - I don't think these are going to be a factor this time around because of the forcings I described last night at some length....but they MIGHT be. Dont shoot the messenger if it all goes wrong - but if I'm honest I'm feeling pretty good about the alignment of things at present and in particular about the longevity of what may occur. Bear in mind that week beginning 21st January is likely NOT to be the peak of the process. If you prefer computer driven analysis then just look at the oft shown EC images for end of Jan into Feb for evidence....but the downwelling impacts of the SSW and the next phases on pacific forcing say to me that the peak will be somewhere in the last few days of Jan and on into the first couple of weeks of Feb. Historically probably the UK's sweet spot in terms of snow fall. Watch and enjoy the ride.
  16. 102 points
    Welcome to "Celebrity Model Discussion". Let's go out to our reporter, who has managed to corner the miracle man himself, Jesus Christ, for his thoughts: Reporter : Thanks for joining us Jesus, first can you give us your view on the overall synoptic situation? Jesus : Well, we currently are set for a PM blast later in the week, then a Northerly flow. JC : Of course, the longevity of this is the real matter to be resolved but it seems most likely that the cold will prove hard to shift. R: How about a chart to back that up? JC: (sighs) very well, here you go..... JC : After that, I expect High pressure to exert itself over the UK. R: So a MLB then? That's not going to be very popular with those awaiting a more continental 1963 style snowfest. JC: It is easier for a camel to pass through the eye of a needle than it is for high level blocking to set up to bring an Easterly to the UK. R: How about that huge Siberian High? Maybe we could get that to move Westwards? JC: I don't know, you'd have to ask my Dad about that.... R: Have you got anything that may cheer up those who want an Easterly? JC : Well, P3 on the GEFS is rather nice tonight. R: And you think that is a real possibility? JC : ........... R: What about the forthcoming cold spell though? Surely there are chances for snow then? JC: Blessed are those that live in the North. Also those on hills, for they are closer to God. R : So, what would you say to those in the South re snow prospects in the near future? JC : More runs needed. R : Jesus, thank you......
  17. 101 points
    ??????? Eh? The next 7 to poss more days are signalled as below average!! The next 2 nights look firmly set to be coldest of this autumn!! I suspect there's people so obsessed with snow forecasts that they're not seeing wood for the trees. No cold: no snow. And as I posted above, usual suspects in media aside, nobody sensible has given a snow prognosis 10+ days ahead... because the forecasting science to do so with any reliability doesn't exist. Honestly, compared to some recent winters(!), I fail to see anything in longer range models to make cold lovers moan.
  18. 101 points
    Righty-Ho. This can't pass without comment. Below follow just a random snapshot of detailed medium range briefings from Ops Centre made in first days of Jan, looking towards what was then the 10-15d trend (and now current-short term) period. I will leave it to others to judge if my UKMO colleagues have got things "so massively wrong".... Written 1 Jan: "The unsettled conditions continue into the trend period but with some evidence of increased meridionality in the upper pattern and so allowing for some greater space between systems and perhaps increased signal for some clearer/colder/showery conditions between." Written 3 Jan: "Latest f/c output continues to indicate a continuation of the predominantly mobile, and often unsettled, theme, with periods of wet and windy weather interspersed with clearer/colder weather. Some EPS members continue to indicate the risk of very deep areas of low pressure crossing over or close to the UK at times, bringing the risk of locally storm-force winds mainly, but not exclusively to N’ern areas. A few of the more S’ly tracks (currently about 10% of members take lows across Wales and England) would allow the entrainment of colder air into these systems, with a lower risk of heavy snow developing. All output does allow for transient ridges, but the wavelength of the upper pattern is such that any drier/colder interludes would be short-lived, and there is no strong signal for any prolonged settled spells, or easing of zonality..." Written 6 Jan: "The zonal, cyclonically biased spell looks set to continue for the majority of this period. Further very deep areas of low pressure are signalled to cross the UK at times, bringing the risk of disruptive weather with them, these in turn being driven by a powerful cross-Atlantic jet. Colder Pm airmasses (originally Pc airmasses with origins from N’ern Canada, though heavily modified) are likely to cross many parts between systems, bringing below normal temperatures, and a risk of snow/frost." Need I go on?
  19. 100 points
    ECMWF Monthly goes off-piste versus it's deterministic brother into & particularly beyond Christmas. The +ve GPH/MSLP anomalies out to our NE merely intensify again towards end of month, then show signs of retrogressing 1st week Jan to lie directly to our North, with mean E flow trending more E-NE with time. Glosea likes the idea of a more blocky Jan too... but the term 'deja vu' springs to mind! Other shenanigans aside, at least Glosea strat diagnostics have been sound last few weeks, so given emergent January signals the PV may yet yield a 'surprise from aloft'. We shall see.
  20. 100 points
    EC Monthly consistent with Glosea and it's last runs. Strong resurgence of +ve MSLP/GPH anomalies north of UK further into Dec, especially Xmas week, with marked -ve temp anomalies developing across adjacent contiguous Europe as N'ly flow veers to mean easterly late Dec. Good to see both suites in such firm agreement, despite inherent issues of confidence at such lead time.
  21. 98 points
    It's all good folks - we are about to get slammed Think March 2013 imprinted on the middle of winter - what's not to love ! The slider solutions are dialled in as the wave guide changes, NW SE sliders will be the key feature of the next 6 weeks as the canadian vortex drains itself via downwelling. No it's not 62 or 47 or 2010 But what it actually is an SSW which we all now respect and have learned from, and have the nuance to watch in real time, spilling its arctic cold guts all over the mid latitudes. I am sorry for those of you who think , nope this is not a driver, nope AAM isnt a driver, MJO isnt a driver, Nino - isnt a driver - you get me? Simply put - they are - and always will be and GWO and AAM possibly the most reliable of the lot! Do not discourage in weather that which you have yet to understand - this science is difficult, no one is ever right, no one is ever perfect, no one on here alludes to that What I want to say is- for us afficiandos of cold, us dedicated individuals, hunting, searching, wanting looking and dissecting everything. We are all good Its near solar min, monster SSW, monster Split. NWP - Bring IT !
  22. 98 points
    That's a good tee up for this.. From a subseasonal and seasonal perspective, the gift that has kept on giving is the pattern over the Maritime Continent. I've used this a lot (to success) over the mid summer and autumn periods as a key driver influencing the hemispheric pattern. It was an excellent lead for the high pressure signal centred over Europe and troughing in the Atlantic. Through September and October, this pattern has remained an only recently has it diverged. This is really useful in understanding why we are getting divergence in the pattern, and key to understanding if or more appropriately when it will return as the key driver. So what am I discussing here ? Well, let's look at the spatial arrangement of sea temperatures across the Indian Ocean and West Pacific. There's a text book signature for enhanced low level westerly winds through the Indian Ocean and easterly winds through the central Pacific. This is evident in surface wind anomalies for the region. Where winds converge, upward movement of anomalously warm air leads to convective activity and again this footprint is evident in rainfall anomalies. What's crucial here is that this convective pattern is mirrored in the upper and mid troposheric levels. Here we see an enhanced (negative) velocity potential associated with a substantive standing wave. Analogues for this provide a clue as to how September - October should have looked.. Compared to observed.. That's actually not a bad match across the Northern hemisphere, allowing for a more blocky type pattern over the Arctic related to other drivers, and particularly within the Atlantic sector. So we have a useful blueprint as to how November and December should pan out, given the likely persistence of the underlying driver, the spatial arrangement of SSTAs in the Indian Ocean and Maritime Continent. However, in the last week we've seen the modelling develop a deviation from this pattern. Why ? The answer to me lies in destructive interference from an emerging MJO wave. GEFS and EC EPS are consistent on the development of a convectively coupled wave moving through the central Pacific and Western Hemisphere (phases 7-8-1). Composite for these phases, and you'll understand why we're seeing the trough signal over NW Europe. Note the development of higher than normal heights over Easter Europe and Western Russia there. That is the perfect geoeffective position for upward wave reflection into the stratosphere. Is that part of the beautiful choreography of the atmosphere to bring about a stratospheric warming end November / early Dec ? So assuming the MJO is a player, where do we go from here ? A stall in the MJO in phases 7 or 8 is unlikely. It rarely gets stuck there. Where it does sometimes linger is the Indian Ocean, phases 1, 2 and 3. This seems unlikely in terms of what we've seen and underlying sea temperatures in the region. That leaves me with a likely return of the convective wave quickly to the Maritime Continent as per GEFS. That may well enhance or excite the standing wave once more. Analogues for this for November / December show a very coherent signal for +ve height anomalies in the mid Atlantic, to which you would need to adjust for greater amplification on the back of zonal wind anomalies (weaker than normal) and warming of the column around Barents Sea. If the GEFS is correct here, we should see a return to the mid Atlantic ridge or even blocking further north in the medium to long range. I would expect to see a Scandinavian trough also emerge. This will be tied into the evolution of the MJO towards phases 4 and 5. One further line of thought is relevant here. As others have keenly observed angular momentum remains disconnected from the ENSO state. For a weak La Nina, we should be seeing -1SD, not +1SD. This is reflective of an atmosphere which is primed for amplification. If the MJO swiftly propagates eastward and enhances the convective / upper level velocity potential over the Maritime Continent, we should see a corresponding upward spike in tendency in relative angular momentum giving a large projection of the GWO towards phase 4. Analogues for this with a ten day lag applied are interesting.. So for the next 10 days or so, cyclonic and troughy over NW Europe, temps not far off average or above. Thereafter, would expect to see a transition to a more blocky type pattern with height rises in the mid Atlantic and points north over time.
  23. 96 points
    Temperatures are about to start a decline to below average and expectations are for quite a few weeks of that situation remaining, with cold/bocked weather dominating. It could last well into March. Longer range products have only just started reacting to the MJO phase 7 (which tends to have instantaneous response in outcome here) due to lag. Now we can see the direction becoming clearer in GloSea5 and EC Monthly, we await the operational model centres to catch-up. Storm track is expected to become ever more southerly in next 1-3 weeks, with inherent prospect of these passing to S-E of UK and resultant risk of wintry hazards. It's total chalk and cheese change versus winter so far and evidence is now compelling for most protracted period of below-normal temperatures seen for some time. It matches exactly the UKMO Seasonal Team assessment for this winter, but only now is the model evidence becoming well aligned.
  24. 96 points
    The current UKMO view is for a colder set-up to dominate again into the 10-15d trend period, with more progressive solutions in a minority. Possible net result is UK on western bounds of blocking with 'battleground' style issues in west thanks to periodic Atlantic incursions. Latest EC32 from yesterday is an interesting one; it also indicates a signal by Christmas for negative temp anomalies & HP to N; LP to S/SW, but the clusters do show a wide raft of potential outcomes. Anyway, very early days but tentative signs for something more blocked a bit further down the December diary.
  25. 94 points
    Last one from me for 6 weeks before I leave in the morning for Canada . Our experts we use in resort have told me that todays upper air soundings over the Russian Arctic are showing Easterlies now established at 10mb level. They expect this flow direction to run down to the troposphere in the coming days ( the start of the reversing the westerly flow for much of Northern Europe including the British Isles ). This will impact on the models in the next 48 hours. So hopefully some good looking winter charts for you lot just around the corner. Will be watching from far a field with great interest. Bye for now and a happy New Year to all our forum members, young and old ! C
  26. 94 points
    Good afternoon gang ,its nice to be back reading all the posts again ,although i have been lurking .(Thanks to all friends on here for my much appreciated messages over the loss of my wife recently ,THANK YOU ALL ) .Its great to see that the charts are showing some Winter weather , really warms the cockles of my heart .And its the charts which keep us interested not always showing us what we want ,and i,m certain that over the coming winter there will be Prozack moments and of course STella times ,so with the Meteorological Winter looming we can look forward to 364 roughly Runs of the good old GFS ,182 of the ECM , AND HUNDREDS OF OTHERS .Looking around the Internet back last year i looked at many weather forums etc ,and found that ours is by far the best and most interesting around .In my next post i will stay on Topic ,just wanted to start with a light Hearted post today .Let the hunt for Winter Synoptics commence ,Curtain twitching ,hiding behind the settee etc ,cheers gang ,.
  27. 93 points
    EC week 4, let's just say, what price a white christmas ? Genuine -ve temp signal there at that range is stark. Week 3 continues the theme as discussed, cross polar ridging.
  28. 93 points
    A few of you have asked today about rationale for the (tail-end of) UKMO latest 30-day outlook. There is, of course, a dedicated thread elsewhere for this but I'll just confirm that GloSea5 output remains the rationale behind the wording of the outlook towards end Dec-New Year, with some interesting/intriguing signals into that period. That's all I can share at present.
  29. 93 points
    On the face of it, model output in general favours continuing SW flow, vigorous LP activity over much of the Atlantic, and HP near enough to the SE to minimise any rainfall there. However, there are some interesting hints of changes for later in the month: 1. The US/Canada upper vortex is gradually pushing E, whilst the jet is moving progressively further S. 2. Although much of Europe is shown by the models to be HP dominated for the foreseeable future, an interesting feature appeared on the 12Z GEM with HP building over the Pole. 3. When LP activity starts to decrease in the longer-term, with a very large upper vortex likely covering much of the central and eastern Atlantic, as I mentioned the other day, it sometimes happens as the main LP fills and any frontal activity is travelling E on a low latitude, pressure starts to build to our N, as suggested by the latest GEM. 4. The GFS is showing the polar vortex WAY south at the end of the run, so, should that prove to be the case, intense HP seems likely to form over much of Canada and the N USA. This does I think, favour keeping the polar front and jet a good way S. So, as I see it, 2 weeks of mobile and mostly mild weather then a gradual shift to northerly blocking taking place, and we know what that could mean! The position and strength of the jet will need watching through. If it stays well south then when the final LP of the current stream heads E to the S of the UK, it might pull the old Atlantic LP SE with it, with LP transferring to the Mediterranean, followed by N or NE winds over us. A long way off yet, yes, but it remains a possibility I think.
  30. 92 points
    So to repeat what I just added over on TWO bin all the GFS & ECM suites go with a total pattern change in the next 12-24 hours to a very cold easterly at 144-168 quote - Appologies for any spelling- tapping on phone Just to add to me comment from earlier as I have half hour - I can assure everyone I wouldnt just post & comment If I didnt believe it would have a strong probability of happening- I have been saying the same for days on NW but maybe not as clear & as loud - As it stands there is no ensemble support ( less than 10%) for what im saying but im drawing on what ive seen over the last 14 years - watching every run ( winter ) of the AVN > GFS UKMO & ECM right back to the old snowatch days - I guess in those 14 years the amount of runs modelling scandi / Russian highs delivering deep cold to say debilt at 120-144 have been averaged about 2/3 a year ( obviously thats all the runs for 1 outcome grouped together each time ) & of those 40 odd scenarios the deep cold has penetated to the UK probably a third of those occasions - my memory highlights Feb 2005 , Feb 2009 , dec 10, jan 13- Mar 13 ( rem the undercutter ) but of course some more - also the pain of many failures- I would also add that across those 40 scenarios as a rule of thumb the AVN / GFS is as useless as they come - & to top that the GFS ensembles are the cherry on the useless cake - The ECM has performed well - however its lost some of its kudos in recent years - The UKMO has been pretty consistent but of course has occasionally got it wrong- I would like to think I know where to look when seeing these models & what their weaknesses are - GFS never seems to model the scandi blocking well but also its secondary weakness is not having the resolution to seperate parcels of energy ( PVA ) So when you have a scandi block & are reliant on the models deciphering how much energy is seperated & heads SE so the GFS is at its weakest - it will always move the jet through the block at a NE angle until it gets to grip with the real solution - this often arrives rapidly in the 96-120 arena on operationals & usually a day later on the ensembles - so the integrity of the GFS suite today at 144-168 is pretty flakey. The NE angle of attack is then replaced with a SE angle of attack - The euros will be much more realistic & should be prone to less swings ( again ECM has been showing occasional inter run volality since the upgrade - ) Its also become more apparent to me that theres ALWAYS a trend in the days modelling - sometimes its blindingly obvious - sometimes more subtle- I look for these trends in the places that will impact the Uk in the following days - so thats not overhead -& in this scenario its the development & angle of the dreaded shortwaves coming around the high over russia - to the angle of the waves exiting the coast of the US- These nuances & changes at say 72-96 are the ones that have the 'big' impacts on the pattern at 144-168 I find this far more interesting than chasing future possible teleconnection changes as they are far more specific to the UK- which in my view is of course more important - Anyway- We are at the exact point today where a CRITICAL element of the resolution of the energy distribution will have large scale impacts on the pattern feeding Europe ( NW ) including the UK at 144-168 The models for probably 4-5 days have had the MAIN low arriving at 120 stalling out somewhere close to the NW of the UK allowing energy underneath to be sufficient to keep the deep cold east past Debilt- They havent allowed any lows to 'turn over' & advect the cold back west... ECM & GFS 00z both support this scenario by developing a wave off the gulf at around 84-90 which aubsequently gets swept up in the eastward jet ( flat no amplification ) this wave then comes under the parent low at 144 & slides across southern england giving a very brief continental flow on its Northern flank - (ECM 00z + GFS 00z) However as the flow behind it sees additional phasing of low pressures in the atlantic & the subsequent development of the deep circular low - it all sweeps east with ease- Goodbye block-:( Also to the NE towards Norway the models have placed another shortwave with low heights there traversing WNW- this again stops the block forcing ESE towards the UK. So in isolation - theres just 2 shortwave features both conspiring against the UK for cold... But what if the trend of the day was to change the modelling of these in terms of positions? Well then the longwave pattern will follow- Its my proposal that as we reach 72-96 the models will resolve the heights over Norway & across to iceland & as a result will display heigher heights that originally predicted - Vis a vee the Cold air advection heading westward out of the continent will have more directional forcing WSW not WNW Now to address the atlantic profile - The initial deterministic resolution shows a flat jet with one wave exiting the US on a trajectory with the south of the UK under the parent low, but what if the models are going to react to the downstream changes of heigher heights over Norway with upstream teleconnective changes of more accute amplification - IE creating a ridge with perhaps 2 areas of energy exiting the states - If this happens & you throw a ridge in there then you get an inflection point - the sharper the ridge the sharper the inflection point- All of sudden the wave heading for the UK becomes very very shallow & recurves south towards spain & portugal .... Whilst the other area of energy - again becoming more defined & deeper as it traverses a steeper thermal gradient into the lobe of the vortex goes NORTH west of the big low over the Uk- The net of the this is all of a sudden theres energy heading south to portugal as well as a ridge building over the top of our UK low - forcing it south ( not back NW as the GFS keeps doing ) Bonus wise here is the fact that there no immediate energy against the block over southern england - We then allow the CAA to burst west into the UK ( as long as the low exits southern england & doesnt stall ) If it stalls in the south then its just te North that benefits from the Easterly flow. So these 2 key events - if they are the trends of the day & what ive seen the atlantic ridge has shown on the * UKMO 00z * GFS 06z ( not acute enough ) * JMA 06z t84 has the ridge * APERGE 06z t72 has a ridge forming.. I would expect a significantly different suite tonight in favour of cold. Its happened before - I have called that before ( but of course I have also not been right ) Take it or leave it S
  31. 92 points
    UNDER EDIT do not reply Afternoon All........... The clocks have gone back, the nights are drawing in earlier - so that can only mean one thing: Yes the long road into Winter is nearly over! With just 5 weeks to go to the 1st of December - this is just a preliminary look into what's developing pattern Wise for the Northern Hemisphere & then in relation to that- the potential Winter weather for our patch. I am building the bulk of the forecast around the 'measure' that's held everyone's attention this year the OPI ( October Pattern index ) & when November is nearly out I will revisit this plus the other Winter indicators from November to go again for a final winter forecast. I will also using the modality of the QBO to remove some of the available analogues & iron out any wrinkles.- Other indexes in the Mix like Sea ice decline feedbacks,Ozone / ENSO state + sunspot cycles & finally the stratosphere will be taken into consideration for the final forecast. In terms of using the OPI measure you don't have to fully understand it, although of course it helps. So at a broad-brush level the OPI is a numerical assessment of how organised & directional the Polar jet is. The more positive the index then the jet exhibits little weakness on its journey around 60N. If the values become negative then what this is equating to is really the early indications that the jet ( driven by the organisation & strength of the polar vortex ) is not a strong as normal. At this point, if you don't want to know any more regarding how its calculated then that is all the info you really need to paint a picture in your head that the more negative the number the weaker the jet. Which is good news for the UK for Winter. Its important at this stage to highlight that statistically the information provided by the Italian forecasters who developed this measure presented data to suggest that the correlation between the OPI & the Winter time AO index is of the order of r=0.9 That covers ALL months - positive & negative. Here is the loading index of the OPI- which is where you would find the anomalies in pos & neg years. ** The drawback with this data is that it spans 1976-2013 some 37 years & of those years only 1 is a forecast ( 2013) with the rest being hindcast data- Where the hyposthesis of this index has been compared with actual information. Of course with readily available information there could be the temptation to ensure your outputs reflect what was actually delivered hence damaging the integrity of your new forecasting tool. This method is likely to be peer reviewed in 2015, & with the likes of Cohen on board I doubt that's the case however its important to mention it & to keep this in context with how the OPI performs against the final AO figure for 2014.** For reference the OPI forecast for 2013 of 1.64 & had a Westerly QBO. In terms of analogue data there is only 1 year- 1992. Lets see how the model performed V this small sample size. However before we do I want to add in the consideration of what front loaded means for pattern matching. For me front loaded means that the front portion of Winter ( Possibly even including November ) means a signal will be strongly correlated out to the early part of jan & then post that the signal & subsequent correlation could become less significant as different variables & feedbacks change across Winter. So I would say the OPI is probably front loaded for the first 6 - 8 Weeks of Winter & will no doubt correlate reasonably with the AO for November. So for 1992 here is the Winter 500 MB Height anomaly & the DJF Anomaly 1992/93. You can see a VERY positive AO pattern with the jet blasting FLAT across the UK, & for winter 1992: Again a VERY VERY strong signal there a positive AO, one of the most positive of the last century. Now take the premise that the OPI is front loaded, look at the stats for 2013- November 2013. DJF 2013/14 As we can see similar in terms of the heights,but not as strong as 1992, also The Winter was very front loaded to the OPI- if we take December & Nov we get this- This is much more inline with 1992. So a front loaded + OPI index worked pretty well last year. For 2014 I expect an almost night & day result for the month with my final forecast for the OPI 2.10 - which makes this the second negative OPI in the recorded History. Only beaten by 2009. However we can make some assumptions about yesteryear- pre 1976 from these 2 links http://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/monthly.ao.index.b50.current.ascii.table We are looking for years with -2.0 AO.s ( super AO's) why? * Because the correlation is r=0.9 then working the equation backwards it would stand to reason that the AO > OPI relationship is good for AO Winters with Super AO months of -2. * I would say looking at the data the sub -2 years are: with their CET next door ( DJF) - Average is 4.6 3.8 3.8 1899/1900 2.2 4.4 2.6 1916/1917 1.9 1.6 0.9 1928/1929 3.4 1.3 0.4 1935/1936 2.8 3.7 2.6 1939/1940 3.2 -1.4 2.6 1940/1941 3.8 0.5 3.5 These are the years the NOAA cannot produce images for so we have to correlate CET to AO. As you can see statistically its Below - 15/18 Ave (+or- 0.2) 2/18 Above Ave 1/18. So its 83% odds on every month below ave month. If we move onto months that we can generate charts we get 1958/1959 4.7 1.6 4.4 1959/1960 6.0 3.8 4.1 1962/1963 1.8 -2.1 -0.7 1964/1965 3.6 3.3 3.1 1965/1966 4.7 2.9 5.7 1968/1969 3.0 5.5 1.0 1969/1970 3.3 3.7 2.9 The Averaged OPI loading pattern is below for these months..... - Looks pretty Negative. So what do the Blue & red + Green>? Green = QBO Neutral Blue = QBO East ( negative phase ) Red = QBO West ( Positive Phase ) The _____ is the month of the SUPER AO -2. & onto the Measured OPI Years. 1976/1977 2.0 2.8 5.2 1978/1979 3.9 -0.4 1.2 1984/1985 5.2 0.8 2.1 1985/1986 6.3 3.5 -1.1 2009/2010 3.0 1.4 2.8 All of the above are sub -1.5 OPI's so we don't need to present the Loading pattern as its already been Done. So for 2014 we have 7 years worth of Analogues with all the data ( 21 months)- So can we see why some months were warmer & some were the very best Cold months...? Here we go for the non cold months DEC MONTHS 3 JAN MONTHS 1 FEB MONTHS 3 it is VERY VERY clear that for Jan & feb at least whilst there was a significant -AO we were scuppered in the UK by a Westerly Based -NAO.... Now for the Cold Months- DEC MONTHS 3 JAN MONTHS 5 FEB MONTHS 4 I will leave it here now, without further analysis to present. This would be the preliminary forecast. statistically almost a dead cert that East QBO & -2 OPI brings at least 1 month of Super -AO & a probability of 2 if not 3 months of junior -AO's ( up to -2) The month with the strongest probability of being the Coldest is January 2015, with a high Chance of a Strong Super -AO & easterly Based -NAO. The Overally CET is expected to be below average - at around 2.75 Perhaps divided around something like this, 3.8. 1.5 2.9 Heres the overall picture anomaly wise DJF- December hinges around the onset of wave 1 activity & how it can influence the blocking in the right place... what could be the biggest problem-? West based NAO...... Cold Stratosphere Down welling - Many thanks for looking..... S
  32. 92 points
    This supposed 'return to mild' phraseology seems to have crept-in lately to some posts (perhaps misinterpretation of the term 'zonal' regarding upper patterns, and/or people assuming the words 'zonal' and 'mild', or 'westerly' and 'mild' are somehow synonymous: they are not). The UKMO have at no time in recent 6-15d forecasts indicated 'mild' temperatures in the forseeable. Average for some, yes. But it's late January and by definition, that's NOT mild. The phase through which the easterly regime of next week ultimately later gives-way to Atlantic (weak) mobility has already been flagged as open to great uncertainty (refer to my post yesterday citing the Dep. Chief on that very issue, and the high level of entropy that was exhibited in analysis yesterday re days 8-9). It could be manifested Friday; or maybe not until after next weekend. Or perhaps not at all in an immediately marked sense. The midnight suites have merely compounded that difficulty and so quite understandably, Exeter are leaning away from being too prescriptive on the timing and net result of any swing back to a westerly regime. The latest comments from the Dep. Chief explains very concisely why this uncertainty is currently apparent: "....(a) return to a more W’ly regime will be awkward and unreliable given many eps members show upper patterns with cut off vortices over the UK. This would steer low pressure systems S and allow for renewed cold conditions from the east at times. We are happy... (he refers to UKMO forecast assessment, as it stands today) .... with the overall unsettled signal but with lots of variation in the members, confidence in details will be extremely low." With this in mind - and ahead of whatever the 12z suites offer - can we please exercise caution in misrepresenting the UKMO view re anything 'mild'. They are not saying anything of the sort. Cheers...
  33. 92 points
    For the newbies - a note a caution that alongside variance in the timing and scope of onset of any colder easterly feed, much as the models currently portray, don;t take the cessation (e.g. as per 12z GFS) too literally either. History shows us that once established, such cold takes some shifting and inevitably, the models exhibit set tendency to sweep the blocking aside and take us back to mobility. Thus, whilst we are still at tentative stages re onset (and any initial consequences, e.g., snow perhaps from Midlands northwards early next week, as the system from west Sun-Mon quickly occludes-out), we are most certainly nowhere close to estimating wht on earth happens thereafter. So, please don't take the model 'closure' of the blocked signal for granted.... we've been round this circuit before in recent winters!
  34. 90 points
    Microscale detail absorbing an awful lot of attention on here, when in reality it is a waste of emotion. The macroscale pattern is now fixed - it will not change significantly now for the start of next week, and while we can hopecast for a front/kink/trough to appear in exactly the right place for every IMBY desire it is frankly impossible at 7 days' range. We wouldnt even try to get that right on a standard westerly atlantic pattern - how can we hope to get close to specifics 5 - 10 days out from the main event when we are seeing dramatic events unfold in the strat? Remember - we are still in reversal for several days yet, and the models will have larger than usual error bars on microscale events. We couldnt hope for a better anomaly chart to see in the new month and this is a belter from GEFS to kick off the week on Monday And the strat? By day 10 it has reformed over the pole as the reversal ends, but the shattered remains at 10hpa are weak, and a large eurasian block is still in place while zonal wind profiles recover to weak levels over the pole, but see a very muddled profile at 55/65N suggesting anything but a recovery. Sustained chance for high lat blocks to survive in situ though the storm track will gently slide back north. Battleground snow? Down at 150hpa blocking clearly still in place over Greenland So - 10 days of almost zero chance of a substantial change to the pattern, and decent confidence in any recovery from this point being slow and painful for the vortex. Next week will be very cold as we know...and the week after will also be cold, quite possibly for all parts throughout the week. Confidence then less sure by week 3 - need to see how pacific forcing may impact at that point, and just how quickly (if at all) the vortex recovers. If it is too late for a recovery then kiss goodbye any early spring as cold will continue to spill out at times right through the month in all probability. And what about snow next week? Well - I think all this hand wringing over each individual model is a waste of energy.... but maybe history can help. 3 days before we were hit by substantial snow in 1991 the charts looked like this 3 days before the snow hit in 1987 We are forecast currently to look like this in 72 hours BUT we know we have an SSW in the bag and a signal for sustained blocking and a retrograde pattern Which would you rather have?? Both 1991 and 1987 delivered plenty of snow. What do you think is likely from here if they are analogues to go by in terms of snow fall... - and what about the signals for longevity listed at the top of this rather long post?? The only thing going against us this time is the calendar date. All very very good. People criticising this setup really and truly need to get their history goggles on and then wander off to a quiet corner, tail between legs.
  35. 90 points
    Evening Guys - Well its been an utter rubbish day on the model front- last nights call was based on the european models- more especially the ECM displaying the exact scenario & evolution it did in 2013 & the UKMO had joined the party on the 00z ( tues ) but did move away yesterday 12z- The GFS was to flat to start with & the ECM even at 120 was to amplified- the median point yet again coming out with another stella performance was the UKMO - I cannot praise this mode high enough this year- every single cold spell that hasnt varified- which has been most if not nearly all- The UKMO has never really been on board & perhaps I should have waited till 00z today to post- However when the data is almost identical from the yesteryear right down to the zonal mean dropping again- almost identical to 2013 then it seemed a no brainer. so yep the call was wrong... it may interest a few that this year Im going to work on a new teleconnection, ive not named it yet however it will be based on 2 specific weather patterns that deliver cold for the UK & within that the leads up focussing on MJO data & Strat data - for example, since 1979 there have have probably been around 15 -20 greenland highs - it will be interesting to see my results of what the zonal mean was when these developed, especially in non SSW years - have we had any GHs in non SSW years... Anyway - enjoy your eves -- im as frustrated as anyone ... S
  36. 90 points
    Evening All For those of us who have been here for a long while there is times when you know you have to throw in the towel on chasing cold & times ( very rare ) when you 'just know' that the Cold solution is correct - Today is one of those rare occasions ( last seen nearly 4 years ago ) when what I see developing in the models & more importantly 'how' its developing gives me near 100% confidence that we will see things panning out close to the ECM - Lets recollect the last time this happened & pick these 4 days you will note the start date of the trough dropping south is 13 Jan 2013 The UKMO 4 days before http://www.meteociel.com/modeles/ukmo2.php?jour=9&mois=1&annee=2013&heure=12&archive=1&mode=&ech=72&map=&nh=0&carte=1021 The ECM 4 days before http://www.meteociel.com/modeles/ecmwf.php?jour=9&mois=1&annee=2013&heure=12&archive=1&mode=1&ech=72&map=0&type=0 & the GFS 4 days before http://www.meteociel.fr/modeles/gfse_cartes.php?jour=9&mois=1&annee=2013&heure=12&archive=1&mode=0&ech=6&runpara=0&carte=0 If you run each model through you see the clear issues that GFS has which is eastward bias & not splitting energy .. Today we find ourselves in the same boat- GFS not splitting energy & moving the whole lot eastward- it will take the GFS 24/36 hours to catch up- Its also worth noting why the seasoned campaigners on here show 'little' interest in the ENS means - Assuming the ECM OP is close for day 6 with the ' wedge ' - ( ignore the shortwave flow ) look at yesterdays Day 6 ENS means - very poor from GFS ECM 00z poor 12z ECM 'trending' So those posting Means charts day 8/10/12 - even 16 look so foolish so often ... The only thing to do is reviewing trending... Anyway- sound the alarms - The train has left the station & its on its way !!!! - just follow the evolution from this- http://www.meteociel.fr/modeles/archives/archives.php?day=9&month=1&hour=0&year=2013&map=0&region=&mode=2&type=ncep Moving Over to the strat - The warming that Many of us have been forecasting / following over the last 10 days is now coming to fruition & the initial prognosis of a double dip drop in zonal winds looks to be the form horse ( as opposed to the straight plummet to negative ) The zonal wind @10HPA Over 60N is now is a state of freefall - peak value just 5 days ago was an elevated 48 M/S ( climo for late jan is 30 M/S ) - we will reach the climo line tomorrow & the 20 M/S line 2 days later indicating the deceleration curve is about 5M/S per day - So before the short projected stalling of the first dip the minima will be in 5 days around 18 M/S - There is around 95% agreement ensemble agreement - Post that there is a solid 50/50 split in the warming & deceleration becoming an 'official' SSW with the wind going negative Seen here This is why the albany site forecast doesnt get below zero because its the mean - when in reality its a 50/50 chance with ob iously the lower the better numbers.. What I personally believe about whats happened today in the models - is through high entropy the ECM has resolved the tropospheric response quicker than the GFS -& just highlight This is NOT MJO related for anyone who says it is as its still sat in COD - If you want further proof of the fact that its a tropo response then look no further than the zonal wind data @60N for the dates above - The wedge developed on the 10th of Jan 2013 - This is the merra data Look close the 15M/S day was the 5th, the wedge was there on the 11/12th - see below The was also some pacific response as well - now look at the temps & locations... So in summary: This is 2013 revisited- with 'hopefully' deliver a similar outcome in the short term quick troposheric response as well as the 40-50 day AO profile that encompassed March 13 record breaking -AO as well ( we do probably need the Full SSW to deliver that ) best S
  37. 90 points
    Thanks for this Barry You are however wrong on both counts you suggest : 1) I have explained in extended detail, as much as I am able, the progress of the patterns thus far from autumn (see first posts back in October in OPI thread and then continued on this MOD thread thereafter last month and into this). Many of these posts have had copied entries to illustrate continuity of thought so that progress can be checked and thereby form a very transparent check for accuracy. But most importantly of all (as far as I am concerned) for learning when mistakes are made - as they most certainly will be in a science as complicated and unpredictable when it comes to evaluating weather and weather patterns. 2) Its the first week of December with at least 11 weeks of official winter remaining. None of my posts have proposed any 'dead cert pattern change' till the second half of December at the very earliest. The key here though is 'very earliest' because there was an outside chance (as I and others more technically gifted than me had observed) that the accelerated advance cold pattern feedbacks apparent this autumn might deliver an earlier route to polar vortex demise sufficient for deeper more extenseive cold to arrive than the polar maritime incursions this coming week. These toppling events on their own are still more than last winter managed to muster in its 3 month span.... The feedbacks discussed on here and in places like the stratosphere thread are based on scientific theory which have a large element of proven success - otherwise we wouldn't have analogues and composites to draw on from previous years. Once again - a marvellous opportunity to observe progress and try to learn something. If it snows at the end of it all, then hey well that is a large reward in itself for watching and hopefully learning something Far better, I think, than moaning one week into winter because premature expectations for instant gratification of preferred weather type haven't yet been granted or don't appear to be granted in the heart of December time period . But again, this brings us back to managing expectations, or, if you don't mind me saying so, your own inability to manage them. I know for my part, I try to help do this - and hence why your post is all the more bewildering So to more of the facts, rather than incorrect perceptions : The shorter term sees a very seasonal prospect with an often below average week ahead with high impact weather conditions expected. High impact conditions that take on a more wintry flavour than those witnessed a year back when a cyclonic pattern was evident. Those in the north and in Scotland will indeed be wondering what the fuss is about with very high winds and blizzard conditions expected most particularly for upland regions. Wintriness penetrating a little further south at times too. It is the modelling following this where the interference of the Azores High as a spoiler appears to raise it thorny head once more again. We see the prospect of a weak poleward Hadley cell. This is supportive of poleward propagating (sub tropical) anticyclones to mid latitudes (i.e Azores High) combined with positive Atmosphere and Angular Momentum (+AAM). The energy budget deficit and then rebalancing in the atmosphere poleward is contributory to a spike in the AO. It is this which largely (probably?) lies beyond your own obvious angst and maybe one or two others. But ( if taken like this in isolation and out of context with everything else that is going on right now, and expected to evolve through December) completely misses the bigger picture. Here are several reasons how and why: Further likely re-enforcing of warming of the western Nino regions is likely to weaken the Hadley Cell, especially as the other hemisphere feedbacks tighten their grip in tandem. Why is this relevant? Weaker eddy heat flux into the mid latitudes occurs as ENSO warming occurs in the region which reverses the Ferrel Cell circulation and meridional mass field/Polar vortex gradient and that, self evidently, leads in turn to enhanced opportunity for stratospheric wave attack to lead to higher latitude blocking. The sub tropical ridging (think Azores High again) is weakened and retracted in this process as the higher sea temperatures supporting these anticyclones is weakened. This is a key to the +NAO spoiling conundrum appearing in seasonal forecasts. But we have to be patient and watch to see when this happens..... Much explained winter SAI feedbacks ( which, despite the recent delays due to a short period of Asian troughing) are back on track to re-strengthen the Siberian High and should resume strong wave activity on the vortex through the second half of December. A +PDO and a cool Kuroshio-Oyashio extension (basically in simple terms two water currents found over the NW Pacific) are a common product of El Nino. Warmer than normal SST's build up over the Bering Sea and Sea of Okhotsch. This correlates extremely highly with a displaced (strong) Pacific Jetstream (tick box checklist so far) and evolution to blocking over the pole. The stratosphere is belying its apparently unfavourable strengthening at upper levels and looks destined to set itself up for a bigger fall by doing so. Best remember that bicycle wheel analogy here. The faster the vortex (wheel) spins..the more spectacular the outcome when something is suddenly jammed right into the heart of it. Think SSW Why should we continue to expect an SSW? We know that it cannot guarantee a cold spell for the UK, but if one is seeking guarantees from the weather than maybe they should seek another hobby and another forum.... In terms of solar background - geomagnetic activity has been at a record low level back to 1932. With the solar polar field flipping polarity (ie descent from twin peaked maximum) no further increase is likely in geomagnetic activity (circa 80 to 90 sunspots) Current predicted and observed size makes this the smallest sunspot cycle since 1914. Current activity comes on the back of two winters with Nina pre-disposed conditions. Ozone concentrations build up significantly on the back of dual winters of nina like conditions and these contribute to an SSW occurring. Taking into account prevailing/ongoing sunspot activity combined with an _QBO then this also points strongly towards an SSW occuring Adding all this to the 7/8/1 phasing of the MJO and Greenland wave activity response still currently well enough on track for late in the month, the massive witnessed autumn Siberian snow feedbacks in complete resumption as head towards mid December, then with the changing wave lengths are increasingly on course to bring about a vortex that might spectacularly resemble a beaten up/crushed coke can into the New Year. An early 2015 SSW, if occurring ( as evidence strongly supports),doesn't guarantee a UK freeze, as much as anywhere else - but if one is not prepared to take the selective wintry prospects of the coming week and wait and watch and test the accuracy of all of the above evolve in progress, then best to save frustration for elsewhere and not to post too much on this thread
  38. 89 points
    For those who think the SSW was a bust take a look at this at T+3 Then look at the NW/SE jet axis over us, then look at the fact that the downwelling has been delayed but is just underway, and winter is not over by a long way. Then go and read up a bit about SSW's so next time you make a sweeping statement you are doing so from a position of greater knowledge. Thank You
  39. 89 points
    C'mon guys lets give @Paul and the mods a break with the bickering and personal digs type of posts after all it is a WEATHER forum and this thread is for WEATHER MODEL discussion I can only imagine how hard it is for newbies to try and decipher what is going on among all those types of posts so if anybody has any issues with posts / members perhaps it would be better to use the report post button / ignore member button or try and settle it like adults through PM's and also remember the couple of banter threads that exist Now onto the models I will refer back to my post from 8th Jan some statements / thoughts that I made in the post on 8th Jan "I still believe that any low pressures that do develop will begin to take an ever increasing NW - SE track (with the majority perhaps struggling to get much past the UK) resulting in some northerlies / North westerlies bringing the first hints at something cooler / colder to the UK " "My key period for this would be 17th Jan - 21st Jan " starting on this point, I am fairly happy with this still as we move towards those dates as it looks like around the 17th will be the first (of what I think could be quite a few within the next few weeks) at a sliding low attempt dont take the position / strength of the low too seriously as this is still changing from run to run but the NW > SE movement is there and a run showing possible north westerly / northerly / north easterly air by around the 21st onward for a few days onto my next statement / thought from 8th Jan "So what could happen after that?" "Well IMO it looks like being the last week of Jan from around 24th Jan - 31st Jan that the possibility of some fun and games with blocking and colder charts will reach its maximum potential so far this winter." Again I remain pretty confident with this, why? IMO there is still a signal for the last week of Jan for blocking to start to develop / take hold there are some more ensembles showing this but I think this demonstrates my point clearly enough AO still set to nosedive first hints that the NAO might head the same way And with the MJO looking like possibly heading back toward / through phase 6 / 7 by then that could also help aid blocking (again I am only going off my limited knowledge on the MJO and also might need to factor in some lag time) (some of the other MJO forecasts look a bit more uncertain / slower to go toward those phases ATM) Also still worth factoring in effects from the strat warming event(s) that have took place during late December / Early Jan. some more thoughts / statements that I made on 8th Jan "A word of warning / potential spoiler would be a west based - NAO which remains a possibility http://theweathercentre.blogspot.com/2012/10/east-based-v-west-based-negative-nao.html Key Points keep an eye on these beginning to nosedive once the blocking gets nearer https://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/ao.shtml https://www.cpc.ncep.noaa.gov/products/precip/CWlink/pna/nao.shtml be wary of the west based -NAO" All of the above are still true / possible IMO but with regards to the west based - NAO perhaps the chances of this wont be know until nearer the last week of Jan and where the models are seeing the potential blocking setting up / developing keep an eye on the ensembles for more and more BOOM type charts appearing in the run up to the last week of Jan I think the first area to focus on ATM would be the potential for slider lows and the possible snowy conditions that they may bring but I still believe the amount of BOOM charts will be on the rise the nearer we get to the last week of Jan. A few extra points I would like to make 1. I wouldn't worry too much about differences in each GEFS suite on the graphs (rises in 850 hPa temps) as slight changes in positions of possible slider lows and later on blocking highs can shift those 850's heavily in one direction or the other and I think we are seeing the usual ebb / flow of the models trying to grasp exactly where each low / high is likely to set up (possibly whilst trying to factor in ongoing effects from start event(s) and MJO etc) 2. How quickly have we seen in the past that things can change and head down a colder / much colder route a la Nov / Dec 2010 & Feb / March 2018 etc (yes there have also been occasions where charts such as "that ECM" where the cold looked like it was on route to the UK and suddenly diverted but I much prefer to look at things with a glass half full rather than immediately thinking that we have no hope / chance of the cold / snow reaching our shores / back gardens) using the 2 years mentioned above as examples and again I am not saying that anything of that severity is heading our way I am just highlighting how much can change within the space of a few weeks (using today's date 14th Jan and 2 weeks from now would have us in the last week of Jan , 28th Jan) taking the 25th November as the end date as that was when the colder air was spreading right across the UK then 2 weeks before was the 11th November 11th November 2010 > 2 weeks later 25th November 2010 11th November 2010 25th November 2010 an example of how quickly things can change / blocking can develop February 2018 - again I will use the 26th February as the end point as this was when the colder air was spreading across the UK so 2 weeks before was the 12th February 2018 > 2 weeks later 26th February 2018 12th February 2018 yes there was some snow around for some but I am highlighting how quickly more blocked conditions can develop 26th February 2018 Keep calm everyone and try and enjoy how the rest of January and beyond plays out, I still think we are in for some fascinating model watching. And I just want to remind people I am certainly no weather expert, I am just having a go at trying to predict where we are heading and seeing how close or far away I am (and if I am miles off the mark I will own up and try and examine the charts to see what happened and how we ended up with scenario A or scenario B etc) ensembles GEM 0z ensembles FNMOC/NOGAPS 0z
  40. 89 points
    After a health scare I have had the best news ever and been given the all clear. What a year it has been weather wise.Just like to take the opportunity to wish Paul,all The moderating team and all the members a very Happy Christmas,Have a break from The forum and enjoy the day with your Family's. Let hope for all us coldies January is a cold and snowy one. All the very best to you all C.S
  41. 88 points
    Unfortunately, there needs to be a recognition that if we share at *this tentative juncture* the exact nature of what we have as Ops Centre guidance, certain individuals will inevitably extrapolate/warp/skew it for certain newspapers... and we want to be 100% clear on key issues/likelihood of possible severe weather in public communication. I appreciate & sympathise how this is frustrating for genuine and well-meaning model-watchers, who can fully understand caveats, but we exist in an age where some very silly people repeatedly seek to scare folk through headlines before any high forecast confidence exists.
  42. 87 points
    Another day and another 24 hrs of model watching. Pub was just about to close last night and we had a few big hitters GP, Fergie etc basically said drinks are on the house. “”12z ECMWF ENS set against model climatology lean pretty firmly in median 2m temps towards below avg (at times quite markedly) out to at least 9 Dec. “” “”.and a big intrusion if the N Pacific ridge into the Arctic towards the mid Atlantic ridge. Strongly negative AO latter stages of the EPS”” Tamara adds a few cheeky Christmas charts and it’s a lock in. Someone talks about previous T240 charts not verifying but soon gets drowned out. The curtains are raised at 10pm as we get’’’’’’’…EC Monthly consistent with Glosea Strong resurgence of +ve MSLP/GPH anomalies north of UK further into Dec, especially Xmas week, with marked -ve temp anomalies , Bets are taken on a white Christmas This morning Today's outputs all point to the same trend in terms of some increase in amplification upstream and more digging south of troughing in the Atlantic but early differences mean the weather for the UK could be either a spell of milder sw'erlies or staying cold 06z following the 00z so far with the high sinking south allowing south westerlies to come in though not in a reliable time frame by any means. That’s south westerlies mentioned twice , they better stay outside of the reliable time frame toss*** No real changes in the outputs with the GFS still showing the threat of mild SWlies and the models in general showing a high pressure dominated outlook. Ok that’s enough south westerlies aint going to be a buzz word, If high to drift towards the east and we pick up a SE'ly . To be fair the 06z gets closer to the ukmo output between 120 and 144 hours compared to the 00z by shoving the high more over the uk!but goes default and push everything eastwards after that!! The high says make up your f****** mind where am I going ?? Post T144 the GFS 6z doesn’t want to get rid of that SW direction. Into the afternoon The London 00z ens temperatures post 6/12 show more spread then a tub of lard. GFS is all about the shortwave spoilers. Welcome back short waves , make sure you go in the right direction There is a great degree of divergence between ECM and GFS ensembles ,reflecting how the UK high is modelled, no shi* sherlock This show how FI is T96 as that is where the shortwave dramas will be resolved. A BOOM chart 5/12 is posted UKMO T168 Signs of lower Euro heights, particularly on the UKMO but both an improvement on yesterday's 12z runs. We are starting to see a closed off High with greater chances of feeding continental cold this way Well on the sinking high, Fergie has said it is the favoured outcome but UKMO does not suggest any quick evolution toward that solution. if this trend continues, such as shown at T144hrs.The high holding just a tad further north makes all the difference. I thought it was going south east wtf If you want to avoid the GFS crud start praying the UKMO is correct! Early evening ECM backs ukmo!!! No sign of South westerlies on JMA.JMA the new must have model UKMO 168 continues the eastward propagation of the Iberian low & sends a tighter squeeze of Easterlies over southern England - Very cold surface air 4/10 Cold (1 more to reflect the 2m temps down south maybe -10c near Benson Oxfordshire tonight , who lives near there ?. I took 0.00002 off for folks living in north Scotland milder there) For those that struggle with what’s going on I attach two simplified charts one showing how hard it is to draw marge and one showing marge struggling with the block re where is it going to go.
  43. 86 points
    I think too many have already become desensitised to what constitutes a 'fantastic chart' and the seasonal ailment of this thread (which is irrationally mood driven anyway by the more average synoptic charts that are customarily on offer) has taken on a latest variant of becoming superimposed and twisted on the absurd semantic that 'merely' only UK Tundra conditions are being shown and not the Canadian variety. Truly, if you cannot exercise self control in front of your lap-top by the smorgasbord of dessicating cold solutions evident on NWP, especially as we are heading right into meteorological Spring, then its maybe best that a different form of self torture is considered to spare those who take a more considered perspective. This has nothing to do with any regional bias (coming from a part of the country that relies on these increasingly rare sort of synoptic to get a snow fix) its to do with the usual fascination I have for sitting back and marvelling at watching a pattern like this unfold in the greater macro scale. If/when it snows at home, I will be less inclined to spend spare time waiting for when it is next going to snow, or when its going to end - but instead getting out, having fresh air, exercise and enjoying it. And then, when the snow and ice is over, it will be a case of seeing how the patterns evolve through Spring and into Summer - looking for the best that can be on offer for this Island, whose micro climate is fickle, elusive and overly too mobile to the sort of sustained blocked patterns that can be the deeply cold derivative as upcoming next week, or depictive of deep Azure blue skies, sunshine and warmth of the summer. Get used to this reality - it will always be thus
  44. 85 points
    All roads lead to Rome - or in this case a cold spell. There have been some odd comments on here today, given we are on the cuspy of only our second significant cold spell since 2013, and so I'm going back on my last post - and instead of looking only at short range charts from here it might be good to make some connections and map out the road ahead. Strat first of all. We have seen a slow downwell - no doubt about that - and a fairly chaotic displacement/split event that was uncertain for a while. But the mists have cleared, and the downwelling is finally going to impact more substantially on the trop pattern in the coming days. The atlantic profile for midweek is still fairly flat but the split has worked in our favour, with the Canadian lobe remaining in situ but the more substantial Siberian shard pushing back east towards the pacific. The 150hpa forecast 5 days later quite clearly shows this and you can see the push of energy at 30hpa moving away from Europe over the eastern Siberia with the Canadian shard sitting in place The signal for a resurgent midatlantic ridge up to the N/NW is quite clear. Picture those EC46 images showing more robust northern blocking by month's end - part of downwelling strat forcing. But we have a pacific signal that looks to be marrying up. Our current high has been resilient, but at too low a latitude for our liking. No getting away from that - forecasts a month ago saw the blocking, but saw it further north. The slow speed of strat impacts probably wrecked this possibility. Now torque effectis, apart from in the tropics, have been on their way down....but before long the bounce back up will begin again, and lag effects will time perfectly with maximum impact of strat downwell So we have the beginning of strat impacts to come in 7 - 10 days followed by GLAAM support 7 - 10 days after that. All good. But the story does not end there - the MJO, which on its own was not enough in early Jan to override other factors, is heading swiftly back around to phase 6 - 8 in time for February....so that just as the atmosphere needs a bit more of a bump to keep blocking in place - it gets it. Note also that the MJO is remaining generally active, and poleward wave activity is therefore going to remain a factor in preventing any flat pattern from getting a hold once again. Ventrice filtered plots remain quite impressive So - this takes a pattern of parallel forcings supporting a meridional signal and anything but a westerly atlantic pattern well into February. But let's finish on the strat…..because of all the factors that drive our weather it is becoming increasingly clear that impacts on the vortex that downwell to the trop are dramatic and forceful. The warming that started well over a week ago is just past its peak, but winds at 10hpa are set to remain easterly until the back end of the month, give or take At the same time westerly winds will return at the top. Bad news? Not at all. A return of westerly winds at the top will form part of the ongoing downwelling process - and just as we had a flushing process of westerlies pushed down into the trop round about now, helping neutralise attempts at mid atlantic to greeny height rises, so this flushing out of easterlies will serve to force them onto the trop pattern. Given that the 10hpa pattern will have been reversed for the best part of 4 weeks, we are facing a long process in this regard...and so the gradual recovery of the vortex will actually sustain a reduction in tropospheric westerlies for a long time also - I'd suggest most of February. And then in March the vortex is fading anyway. Will we get anything like enough westerly momentum to change the pattern out of the entrenched cold cycle? I'm not sure we will.....but that is a bit far off to be discussing in detail now. So - forget op runs in 8 or 9 days time that are making it look as though a resurgent trop vortex driven from Canada is about to fire through the atlantic. It isn't. a Canadian trough will remain in place as the strat image is imposed upon it - but the door in the atlantic is going to be slammed shut, and cyclonic energy will have to circulate around the edges. Cold northerlies or undercut scenarios. And if we can get slices of that cold Canadian vortex firing moisture down into Europe over the top, or later on potentially underneath, the block then we get the precipitation we want in a cold phase. This on top of the impacts of deep European snow cover that will help provide a very cold feed off the continent at times when the winds turn E/SE. Long post - apologies - but everything is in place for something a bit special. Stop worrying about NWP. It doesn't get a handle on all these processes well....and while there is no way I would want to call the microscale specifics at anything more than 72/96 hours (and always from UKMO and ECM) - we can sleep easy knowing that the macroscale factors are lining up in favour of snowy goodness for the second half of winter.
  45. 85 points
    Meant to post this last night but some forecasters saying mild Christmas. At this range ,about any thing could turn up ,strange year weather wise so far ,snow in the forecast tomorrow , STORMY with it ,plenty of rain next week and signs now of cold cyclonic next weekend . Our local squirrel s took BEDDING to their winter homes last week , yesterday they threw it out to the local polecats and like ,Today they are collecting it all back .went up woodshed just before sunset today and local vermin were BUSY storing winter food .some very interesting weather ahead I feel ,Stellas all round gang ,I'm usually lurking about as weather is always on my mind ,miss my dear late wife . It's great having this great forum , cheers all .
  46. 85 points
    We have waited a long time to see this. Since the beginning of the internet age. We have all wanted to see these synoptics reel in and in and there is a bit of disbelief now it is happening, Phenomenal is all I can say. And to think that there was some that said that we would struggle to ever see these synoptics again. Well I guess that will be put to rest next week. Big time. Normally to just get the -10ºC 850 isotherm over the country for a day is an achievement so to see multiple days forecast is amazing. Look after any vulnerable neighbours whilst enjoying the freeze - but do enjoy what could be a once in a generation cold spell. I'm sure that it is just a co-incidence that this follows a SSW lol!
  47. 85 points
    ...precisely so, and precisely echoing UKMO thoughts after some recent flip-flopping of output (including yesterday's ECMWF Monthly, which suddenly offered substantial weakening of the previously strong +ve MSLP anomaly north/NW of the UK that it yielded in the run only 3 days prior and in all previous recent runs, for later December. Is it wholly trustworthy, given marked swing? No, not until we see the sense of direction offered in runs on Mon-Thurs next week. The situation currently is that whilst ECMWF now offers just a bland, weak +ve MSLP anomaly to the west of the UK, it equally - and quite starkly - offers no signal either to suggest a markedly zonal, +ve NAO set-up either.... In other words, whilst GloSea still remains more inclined to return a blocked story later through the month (and ever since output run way back in Sept, has not budged from indicating a massive ramp-up in stratospheric zonal winds later Dec, as now being suggested by GEFS), the forecast outlook by the UKMO remains quite reasonable in the current circumstances (not least as it would be easy to overreact to latest ECMWF in isolation). Thus, a return to blocking still remains the more favoured outcome, BUT whereas this always had low confidence (based purely on lead time), we now can add a further tier of uncertainty given ECMWF yesterday and the fact that no clear synoptic regime is obviously favoured after mid-month. Some reactions I've seen on social media have been bordering on hysteria, but there's nothing that suggests 'Dec 2015 Revisited' has suddenly manifested in model output. So it looks set to get milder through next week.... but does that really automatically, unquestionably characterise a whole winter ahead??? Deary-me ;-)
  48. 84 points
    Mean while in the real world away from the MOD... A tragic accident has cost 6 lives in Glasgow. yes this is off topic but a timely reminder of just how unimportant the weather really is in our lives... R.I.P TO THEM AND PRAYERS FOR THE ONES THEY HAVE LEFT BEHIND...
  49. 84 points
    With that being the case, Purga, why bother come on a model discussion thread at all? The whole idea of this type of thread is to discuss what the models show, the differences between the models, and what they could go on to show. Otherwise we would all be happy with just watching the weather forecast every evening. Sometimes there is just as much 'eloquent popycock' from a few who are determined to write off every possible cold spell.
  50. 84 points
    Some subtle hints of a New Year pattern change, but it's going to take its time. First, the 500mb flow is fascinating: The most remarkable feature is the sheer strength of the flow across the Atlantic around the base of the upper low heading towards us, quite rare to see such intensity I think. There are changes upstream as the E Pacific ridge fades and once again Pacific systems are heading SE to re-invigorate the upper trough over E USA/Canada. This suggests, on the face of it, more of the same with the jet continuing to propagate in our direction, with the relentless LPs coming with it. However, note the 500mb high near the Pole that's been there for a few days. It may not look much but if it sticks around, once the pressure field across the Atlantic starts to slacken off, it may just hint at HP building. I mentioned this possibility before, but the ferocity of the jet has obliterated any chance of any blocking pattern forming, let alone persisting so far. But in my experience at least, stormy mobile patterns of this intensity cannot sustain themselves for THAT long. So I am sticking with the story I have been telling for a while now, of LP and the upper vortex sinking slowly S and an accompanying flow of colder air, gradually followed by rising pressure to the N and NE. Well, my very best wishes to you all for a good Christmas and my great thanks for so many of you who have added "Like" to my posts, it is most kind and I appreciate it a lot. I hope Santa brings you everything you want! OMM
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