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Model output discussion - after the beast, what next?


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Posted
  • Location: South Croydon
  • Location: South Croydon
    6 hours ago, Gray-Wolf said:

    The GFS MJO tweet from M. Ventrice has me a bit twitched. over 5 s.d. is a 1 in 3,500,000 shot so not a common occurrence at all? The 4 s.d. that propagated the SSW was a measly record 4 s.d.'s and that looped the jet toward the pole before plunging it way to our south. Could the jet, like a swing pushed too hard, make it right over the pole and so out the other side?

    This would place us well on the summer side of the jet and open the doors to African WAA until the Jet can slip back.

    I'm not liking these obscene excursions of atmospheric angular momentum at all ( and I won't tell the usuals "I told you so!") but it is new to me!

    The plot on the graph shows today well beyond 2 s.d.'s and the 7th is off the plot so we won't have long to see if the excursion verifies but I have no idea just what it will unleash?

    Yes odd - clearly that chart isn't -4 to +4 standard deviations.  +/- 2 captures 95% of all observations.  So >4 standard deviations would be so infrequent that this can't be what he means.  Am I missing something here?  Googled +/- 4 sigma and it's 99.993% of observations.

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    The UKMO 144 has teased me out if hibernation - for a comment. 144 shows a very meridional flow across 50N with deep cold filtering into Scandi- could be a sharp transition from mild to cold

    No mate, I'm still in winter mode as long as the Gfs shows potential arctic blasts..hope it continues!❄❄❄❄❄

    Ahhh another chocolate teapot in your post... I believe the last one froze. It seems that we are seeing the second response to the SSW with another surge of negative zonal mean u winds heading fo

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    Posted
  • Location: Lincolnshire - 15m asl
  • Weather Preferences: Frost and snow. A quiet autumn day is also good.
  • Location: Lincolnshire - 15m asl
    38 minutes ago, Gray-Wolf said:

    I still think with one of the drivers showing a deviation over 5 s.d.'s from the norm takes things beyond the programming capacity of the current models?

     

    It's a very bizarre forecast. Such a massive increase in pacific forcing is not "normal" - assuming we know what "normal" is. I have a lot of reading to do this coming warm season... but we seem to be experiencing climate extremes that challenge the record books on a far too frequent basis. I notice that water temperatures in the Gulf of Mexico are extremely high at the moment too. In terms of NWP output I would agree - what we learned a few weeks ago about algorithms and their construction via approximations made would suggest that a pacific spike of the magnitude forecast by GFS via WSI will create some peculiar runs and increased inaccuracy. We are too late in the winter season now I think for any major impacts - but less arctic ice = ever greater energy release in years to come during refreeze = ???? in terms of global patterns? 

    Thanks for the links by the way - plenty to get stuck into...

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    Posted
  • Location: Halewood, Merseyside, (29M ASL)
  • Weather Preferences: Winter - snow, Irish sea convection. Summer - thunderstorms, hot sunny days
  • Location: Halewood, Merseyside, (29M ASL)

    Wrong thread

    Edited by Chris.R
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    Posted
  • Location: st albans
  • Location: st albans

    How often are those AAM charts produced ? I believe they are from ncep data ?  Surely there must be other tools available which back that up or question it’s validdity??  Mind you, having just come off a neg NAO/AO combo in excess of -5, and with a very benign strat also predicted to go back to a neg zonal flow by the 20th, perhaps everything is on the table!  

    Without that small piece of discarded vortex meandering around mid atlantic, forcing the phasing of the upper trough, I would expect to see quite a different set up for the n Atlantic - that could well be a chunk of misfortune having come our way. I note the general draining of low heights around day 10 on the gefs and gem. Waiting to see where ecm op goes on this as an indicator but it seems happy to play with wedges well before that timescale.  

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    Posted
  • Location: Castle Black, the Wall, the North
  • Weather Preferences: Spanish Plumes, Blizzards, Severe Frosts :-)
  • Location: Castle Black, the Wall, the North
    12 hours ago, Frosty. said:

    Surely this from the Ecm 12z, albeit day 10 would be the prelude to an arctic incursion..surely!:D:cold:..see, I'm not giving up on winter yet!:) 

    240_mslp500.png

    Surely this from the Ecm 00z, albeit day 10 would be the prelude to an arctic incursion..surely!:D:cold:..see, I'm not giving up on winter yet!:)..feels like I'm repeating myself:D:crazy:

    240_thickuk.png

    240_mslp850.png

    240_mslp500.png

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    Posted
  • Location: Somerset midway between Bath&Wells. Mendips 200m asl
  • Weather Preferences: Snow and lots of it or warm and sunny, no mediocre dross
  • Location: Somerset midway between Bath&Wells. Mendips 200m asl

    I know it's impossible to pin point with complete accuracy but from a probability perspective, how likely is it that we will end up with cold, potentially snowy weather again later in the month? If it happens, will it be mostly a northern event or likely to hit the south too? Not chasing snow here, planning work. Any clues gratefully received.

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    Posted
  • Location: Darlington
  • Weather Preferences: Warm dry summers
  • Location: Darlington

    For the next 10 days the ECM mean shows a north-south split Scotland (below) holds onto colder air albeit less cold than last week but still the chance of snow now and then with the mean between -5 and -3

    graphe_ens3_php.thumb.png.c72a67998c08a74719cc5faae342f5bf.png

    Further south the London mean shows milder air making inroads at times one such spell will be around Saturday where temps could get up to around 15c for some parts but the catch will be a fair bit of rain thereafter the mean gradually falls a bit but not going below -3

    graphe_ens3.phpldn.thumb.png.ab6e066cb242ce5389bf945e750db18a.png

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    Posted
  • Location: Horsham, West sussex, 52m asl
  • Location: Horsham, West sussex, 52m asl
    58 minutes ago, jethro said:

    I know it's impossible to pin point with complete accuracy but from a probability perspective, how likely is it that we will end up with cold, potentially snowy weather again later in the month? If it happens, will it be mostly a northern event or likely to hit the south too? Not chasing snow here, planning work. Any clues gratefully received.

    from current modelling, most likely wet, windy in the south west, on the cold side but not exceptionally so for the south. any snow restricted to the north. not much in the way of spring warmth. the cold can bugger off now, i've got 2 fairly big flat roof jobs to do and the weather isnt helping! 

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    PANIC OVER!

    The atmospheric angular momentum (AAM) chart that was posted yesterday originating from that Michael Ventrice tweet appears to have been a plotting error or a technical fault.

        GEFS AAM Forecast on March 7th               GEFS AAM Forecast on March 6th                  GEFS AAM Forecast on March 7th                       GEFS AAM Forecast on March 6th 

    gfsgwo_1.png         gfsgwo_2.png          gfs1.png                  gfs2.png

    Source: Nicolas Schiraldi - link:  http://www.atmos.albany.edu/student/nschiral/gwo.html     Please note that the March 7th charts are liable to auto update tomorrow morning as the latest (March 8th) data is input.

    The GEFS current and forecast charts are known to have a permanent negative bias and generally understate the global relative AAM anomaly by around a factor of one. At the end of each day, one can obtain a "final analysis" of  AAM with a much more accurate plot of the "current" position from another source. Unfortunately there is no forecast on this site. 

                     GWO Final Analysis with March 6th plot

                              gwo_fnl.png                Source:  South California Weather Notes  -   link:   http://www.sierraphotography.com/wxnotes/weatherlinks.htm   

    Please note that this chart shows the mid point of each phase with a hatched line rather than the full sectors as on the GEFS charts.

    Just a reminder of what these GWO (Global Wind Oscillation) charts indicate in each phase:

                                         gwo_phase_fig4.jpg       Source:  https://www.esrl.noaa.gov/psd/map/clim/test_maproom.html

    There is a normal progression through the phases. For example as relative AAM starts to rise from a weak of negative position through phase 4, Frictional torque (FT) starts to rise. Then as AAM and FT spike upwards into phase 5, Mountain torque (MT) starts to rise. There is usually a 10 to 14 day time lag. It was the +ve MT in early February that eventually impacted on the lower stratosphere and was, amongst other factors, one of the triggers for the SSW. We cannot get torque forecasts but one can apply one's experience of the GWO phases to the GEFS forecast plots (allowing for the biases) to get get a pretty accurate idea of what to expect. I show the torque charts below:

                  FT as at March 4th                            MT as at March 4th 

        gltauf.90day.gif             gltaum.90day.gif

    Just like relative AAM, the torques are pretty neutral right now. Only NAMT (North American Mountain Torque indicated by the blue line in the chart) is trending marginally positive. The charts are usually 48 hours out-of-date and they tend to auto update in the late afternoon. Sometimes a "page refresh" does this. 

    I am still learning a lot about these processes and that is why I set up the "Teleconnections Learning Thread" a few weeks ago. There is a lot of information on there already. It has gone very quiet recently due to all the "snow interest" but later this month we will be opening a debate and post mortem into all the factors that triggered the SSW and what might have produced the record strength event, what affected the speed of the impact and why it caused such a rapid surge westwards. Some of these processes are well understood, some are only just beginning to be understood and some are not yet known. We do not wish to compete with the strat thread but rather to compliment it. The learning thread focus will be on how all the different teleconnection drivers interact and why some are more dominant than others at particular times. We will also be launching a specialist learning thread library shortly as well. I will advertise on the MOD when these events occur. In the meantime, here's a link to the Teleconnections Learning Thread:

    https://www.netweather.tv/forum/topic/89161-learning-about-teleconnection-science-and-background-signals/?page=3

    or you can simply click on the chart below:

    I would normally aim this type of post on the learning thread but it was appropriate on the MOD right now to clear up the misunderstanding in respect of yesterday's probable technical error on the GEFS AAM forecast chart.

    Edited by Guest
    Correct typos and check charts
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    Posted
  • Location: Darlington
  • Weather Preferences: Warm dry summers
  • Location: Darlington

    UKMO extended has low pressure to our west and just a few isolated showers for us otherwise it is fairly dry

    ukm2.2018031400_168_lant.troplant_prp_fcst.gentracker.thumb.png.1c8d7e9d6046276869ea329277560fbd.png

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    Posted
  • Location: Somerset midway between Bath&Wells. Mendips 200m asl
  • Weather Preferences: Snow and lots of it or warm and sunny, no mediocre dross
  • Location: Somerset midway between Bath&Wells. Mendips 200m asl
    19 minutes ago, bobbydog said:

    from current modelling, most likely wet, windy in the south west, on the cold side but not exceptionally so for the south. any snow restricted to the north. not much in the way of spring warmth. the cold can bugger off now, i've got 2 fairly big flat roof jobs to do and the weather isnt helping! 

    Thank you. Doesn't fill me with joy but then snowmageddon wouldn't either, like you I'm looking for spring now.

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    Posted
  • Location: East Ham, London
  • Location: East Ham, London

    Morning all :)

    I have to say that AAM spike got me wondering as well - I did think the Pacific Jet had substantially amplified on the 12Z OP yesterday. While that's being resolved, I'll take a look at the medium range model outlook this morning taking us to St Patrick's Day, Saturday March 17th:

    ECM 00Z kicks off the dancing at T+240:

    ECM1-240.GIF?07-12

    A deepening area of LP is moving N from the North Sea into the Norwegian Sea and leaving the British Isles in a slack N'ly airflow with increasingly cold air coming south and -8 uppers over Scotland. A small secondary feature looks set to head SE across western parts. Showers or longer spells of rain with snow to altitude looks the call. A new LP is developing to the SW and looks set to approach southern Britain.

    GEM 00Z at the same time:

    gem-0-240.png

    LP is centred over southern England and the trough extends east and west to a second main centre over the far Atlantic. To the north, there is substantial HP over Greenland and to the north of Scandinavia. Calm winds over the south but an ESE'ly over northern Britain though uppers are positive for all. Rain or showers for most would be the weather with the worst of the rain in the south.

    GFS 00Z OP at the same time:

    gfs-0-240.png

    An area of LP is centred over the east coast with a second centre further north. A ridge of HP to the west is followed by a new developing LP in mid Atlantic. There are heights over Greenland and to the north of Scandinavia. Over the British Isles a WNW'ly flow is in charge for the west with light winds elsewhere and there would be plenty of rain or showers from this evolution.

    Further into FI the LP remains close to the British Isles but fills in situ as the Azores HP tries to become more influential and at T+384 looks to be ridging toward Greenland.

    GFS 00Z Control at the same time:

    gens-0-1-240.png

    The trough is further west but still very much in charge at this time. A hint of some warmer conditions for the SE corner. Further into FI and the trough disrupts south as heights rise to the north and north west and by T+384 there's a light ESE'ly flow over the British isles but the air source is much further south and we could see some real early warmth with a plume-like push of very warm air north just to the east of the British Isles and the +8 uppers crossing East Anglia which would offer the first 20c of the year if it verified.

    The 00Z GEFS at T+240:

    http://www.meteociel.fr/cartes_obs/gens_panel.php?modele=0&mode=1&ech=240

    Not much argument for there with LP very much in charge. The exact placing and orientation of LP centres varies enormously as you'd expect but the general theme of a disturbed and often wet scenario is there for all to see. Beyond that and it's clear the GEFS are sniffing round various solutions - some, as the Control, bring some early season warmth, some cold and some both (P16 is one to look at). I presume this is a response to the next phase of stratospheric warming so we'll see where it goes. We all know the warmer air mass will win in the end but battle is joined and the British isles is the soggy battle ground.

    In conclusion, if you want dry, settled weather you've come to the wrong place. Apart from a favourable flow in front of an approaching LP or a transient ridge there's very little break from rain or showers over the next 10 days. It's likely higher elevations will continue to see snow and perhaps the snow level will drop further in the far north with time but other models keep temperatures closer to average. Longer term the signal for some sort of pattern change is there but it's very diffuse at this time - we could see some early spring warmth or we could be back in the fridge or we could move from the one to the other very quickly as is often the case as winter becomes spring.

    Finally, a look at the rainfall numbers from the GFS 00Z OP:

    240-777UK.GIF?07-0

    The best part of 4 inches in the next 10 days for parts of the south west and south Wales.

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    Posted
  • Location: Manchester Deansgate.
  • Weather Preferences: Heavy disruptive snowfall.
  • Location: Manchester Deansgate.

    After an uninspiring GEFS 0z suite, a very decent 6z op run, although the initial cold plunge is to our west, its very decent going forward.

    gfsnh-0-312_xjr4.png

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    Posted
  • Location: Drayton, Portsmouth
  • Location: Drayton, Portsmouth

    ECM clusters D8-D15 - trying to revive the idea of an increase in heights to the NW

    ec-ens_nat_z500scenarios_2018030700_192.  ec-ens_nat_z500scenarios_2018030700_300.

    Except perhaps in Scotland, unlikely to mean any deeply cold weather for the UK just yet, but both yesterday's 12Z and today's 00Z seem to increase the NW height anomaly towards D15 - which would increase the chances of a major northerly towards the latter part of the month. I feel that the straight-line northerly can still produce very cold conditions even at this stage of the year, so who knows?

    The other thing I note is the absence of an Icelandic low in the D8-D15 period, with a mean easterly flow over Iceland. This suggests a continuation of low pressure pushing right through the UK, but with possible "back-door cold" as the lows clear.

    So my general forecast for D5 to D15 would be wet, windy, fairly cold without being snowy, though snow potential never far away. More like January than March!

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    Posted
  • Location: st albans
  • Location: st albans
    8 minutes ago, Man With Beard said:

    ECM clusters D8-D15 - trying to revive the idea of an increase in heights to the NW

    ec-ens_nat_z500scenarios_2018030700_192.  ec-ens_nat_z500scenarios_2018030700_300.

    Except perhaps in Scotland, unlikely to mean any deeply cold weather for the UK just yet, but both yesterday's 12Z and today's 00Z seem to increase the NW height anomaly towards D15 - which would increase the chances of a major northerly towards the latter part of the month. I feel that the straight-line northerly can still produce very cold conditions even at this stage of the year, so who knows?

    The other thing I note is the absence of an Icelandic low in the D8-D15 period, with a mean easterly flow over Iceland. This suggests a continuation of low pressure pushing right through the UK, but with possible "back-door cold" as the lows clear.

    So my general forecast for D5 to D15 would be wet, windy, fairly cold without being snowy, though snow potential never far away. More like January than March!

    Broadly agree but I think this is an evolving situation. The gefs at 60N whilst showing a 10hpa reversal within two weeks are also showing an increased zonal flow in the trop at that timescale so some differing factors at play and bear in mind downwelling waves from the SSW 

    not for one minute suggesting there could be a countrywide snow event second part of March but I also am firmly of the opinion that the Scots have plenty of winter still to get through before spring arrives and who knows how far south that threat might get on occasions

    Edited by bluearmy
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    Posted
  • Location: Manchester Deansgate.
  • Weather Preferences: Heavy disruptive snowfall.
  • Location: Manchester Deansgate.

    The recurring theme wrt cold potential is the trough just seems not to want to get that bit further East to open the floodgates properly.

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    Posted
  • Location: East Ham, London
  • Location: East Ham, London

    Both the 06Z GFS OP and Control play with the idea of ridging south from Greenland. The OP starts well but then for some reason changes the ridging to the west and we end with a west-based negative NAO.

    The Control builds a weak mid-Atlantic ridge with a suggestion of an Arctic incursion not far away. Looking at the GEFS in far FI briefly and the signal for renewed northern blocking is clear if not wholly convincing at this time. Both OP and Control begin the amplification at T+252 so we'll see if it gets into my medium range summary tomorrow morning.

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    Posted
  • Location: Cleeve, North Somerset
  • Weather Preferences: Continental winters & summers.
  • Location: Cleeve, North Somerset

    The UK seems to be a trough magnet in the coming weeks, possibly due to cold air never being far away to the north and an increasingly warming 'south of the UK' helping cyclogenesis - first example being this weekend's low. If not for the absence of a coherent PV, I'd say the charts all look a bit November/Decemberish with milder interludes mixed with chilly Pm interludes, all resulting in plenty of rain or showers. Certainly very little in the way of March gales or the fabled spring 'sunshine and showers'. ECM seems most keen on colder air returning later next week but that's all very far away. This weekend, some of the less wet locations could hit their highest temperature since November.

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    18 hours ago, Bring Back1962-63 said:

     

    In the run up to the record strength SSW, the models really struggled to cope with the pattern reversal.                              

     

    The 'record strength' of the SSW has to be put into some perspective - yes the 10mb 60°N wind reversal was the strongest on record over a number days, though over the period of reversal there are only between 5-7 reversals in total out of 40 years on record. For February as a whole, it is the strongest reversal though just less than 1 m/s greater than Feb 1987.

    However, if considering SSW strength over depth of stratosphere involved, 2018 has not been particularly impressive. It managed a few days reversal at 30mb, but 1987, 2001, 2009 and 2010 had reversals as low as 100mb. Indeed, 1987 and 2010 both managed a day of reversal from 10mb right down to 150mb.

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    Posted
  • Location: Mytholmroyd, West Yorks.......
  • Weather Preferences: Hot & Sunny, Cold & Snowy
  • Location: Mytholmroyd, West Yorks.......

    https://earth.nullschool.net/#current/wind/isobaric/250hPa/orthographic=0.97,92.44,311

    We seem to have misplaced our Ferrel Cell.....or is it our Polar Cell?

    Whichever it is I was brought up with 3 Cells in each Hemisphere and not just a sub tropical Jet separating pole from equator?

    The energy that drove the SSW is still reverberating around the atmosphere and we have already seen hints that we are due another huge MJO departure.

    This time lets see the jet hoisted to our north and stay there for the rest of spring and summer!

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    Posted
  • Location: NR LOURDES SW FRANCE
  • Location: NR LOURDES SW FRANCE

    The ECM struggling to get the Atlantic troughing into mainland Europe and drops the tease of the mini beast from the east  perhaps trying to  paying a visit !

     

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    Posted
  • Location: Wirral, Merseyside
  • Weather Preferences: Snow, Sunny crisp frosty days & Thunderstorms
  • Location: Wirral, Merseyside

    Winter looks far from over according to the ECM.

    ECH1-168.GIF.thumb.png.d1cf6a63266bb0c28a7b3a238fdf8618.pngECH1-192.GIF.thumb.png.be947dd4374ba1082d35b4ac1178b89a.png

    ECH1-216.GIF.thumb.png.505dd33b7a8dd9cab31ff521c90c4485.pngECH1-240.GIF.thumb.png.9de0854e857b4e2e77fe730b2f0e23d6.png

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    Posted
  • Location: Drayton, Portsmouth
  • Location: Drayton, Portsmouth
    5 minutes ago, feb1991blizzard said:

    Atlantic trough disrupting and digging south after hitting brick wall, great WAA into the pole and a stonking great cold pool awaiting similar to the one we've just had. Whitney we have lift off!

    ECH1-216_tnm1.GIF

     

    Oh come on ECM. I'm still catching up on sleep from the last chase!

    Seriously, this has no support from the ensembles. Need to see this repeated before getting carried away.

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    Posted
  • Location: Stroud, Gloucestershire
  • Weather Preferences: Extreme!
  • Location: Stroud, Gloucestershire

    One last beast before spring..... well why not give it a go eh ;) 

    IMG_3416.thumb.PNG.0da12f867f2cc1dc80a71012581514b6.PNG

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