Model Output Discussion - 23rd Jan - 12z onwards

[Nick F]

A very cold arctic plunge on 00z ECM down across Scandinavia then eastern Europe from around the 8th/9th with -10C T850s to italy and -15C to the Balkans by the 11th. This occurs, as Steve M mentions last night, when the flow amplifies upstream around the NW Atlantic/S Greenland - in response to a piece of the trop PV dropping SE across the far N of Canada - this allows another lobe of the trop polar vortex to drop south across Scandi.

 

 

GFS has the plunge but further east. IF only we could correct that ECM plunge further west. Potential that the models may not have a strong handle on this amplification - particularly with the breaking away equatorward of the trop PV lobe around Greenland/Norwegian Sea. Though there's only a few 00z GEFS members getting the UK under the bitter plunge. Most GEFS as per operational have us under HP.

Edited February 1, 2015 by Nick F

[joggs]

I thought the azores high was supposed to gradually displace west(through the teleconections)?!

It just sits around us,sorry,its just what ive read on here this last wk or so.

[Gustywind]

Trouble is that big mass of vortex everywhere to our north, eg ecm 240 chart. Really could do with a split up there or strong arctic high to suck up the UK high.

[SMU]

Just adding to Nicks post

 

the UKMO break point of that low

 

http://www.meteociel.fr/ukmo/runs/2015020100/UN144-21.GIF?01-06

 

is considerably further west than the ECM

 

http://www.meteociel.fr/modeles/ecmwf/runs/2015020100/ECH1-144.GIF?01-12

 

 

The polar vortex dropping like I said like last night is still just coming into UKMO range.

 

Thats the key peice to keep an eye on today as was mentioned last night.

Edited February 1, 2015 by Paul
Removed the iffy comments from yesterday

[bluearmy]

More week 2 ens mean/anomoly suites have us under anomolous high heights than low ones though whilst we get run to run variation, the possibility that they are wrong exists. Steve highlighted a potential evolution last night re the models being too Far East. Sadly, the pattern early that winter was far more merdional than this (the astonishing thing about this last week has been the lack of mobility west to east. The upcoming week sees us back to where we have been all season with polar vortex movement to our north encouraging a strong northern arm across the Atlantic. Hence the high begins to sink and it's notable that it doesn't actually manage it. Shows that any different polar profile this week would probably have kept us under the cold trough influence. (The obvious comment being that the modelling has the polar profile right this week which a few years back may have been feasible but I've yet to see strong evidence that the upgrades over the past few years have done anything but improve that facet of the NWP).

Anyway, the point here is that no operational is showing a route back to deep cold within a week and given the lack of decent ens support for anything different, a slow drift to a less cold scenario is strongly likely. Of course less cold aloft may not mean less cold at the surface. That is still to be resolved but it is feb rather than dec/jan so the chances of an inversion leading to ice days are greatly reduced though still feasible.

Until we see gfs ops post day 10 beginning to show a potential cold solution on the odd run, I very much doubt anything unexpected is out there. that's the cue for the 06z to do its stuff!

Edited February 1, 2015 by bluearmy

[winterof79]

I am not convinced the high wiil be over us as per GFS yet.This 144z chart could go another way.Any westward correction and we are in the game

 

[knocker]

A very cold arctic plunge on 00z ECM down across Scandinavia then eastern Europe from around the 8th/9th with -10C T850s to italy and -15C to the Balkans by the 11th. This occurs, as Steve M mentions last night, when the flow amplifies upstream around the NW Atlantic/S Greenland - in response to a piece of the trop PV dropping SE across the far N of Canada - this allows another lobe of the trop polar vortex to drop south across Scandi.

 

ecm500.192.png

 

GFS has the plunge but further east. IF only we could correct that ECM plunge further west. Potential that the models may not have a strong handle on this amplification - particularly with the breaking away equatorward of the trop PV lobe around Greenland/Norwegian Sea. Though there's only a few 00z GEFS members getting the UK under the bitter plunge. Most GEFS as per operational have us under HP.

 I see what you mean Nick but the ECM whips the low NE, with an offshoot nippimg to the Med, leaving behind some very cold air over eastern Europe down to N. Africa but at the same time consolidating the HP and pushing it east.

Edited February 1, 2015 by knocker

[fergieweather]

I thought the azores high was supposed to gradually displace west(through the teleconections)?!

It just sits around us,sorry,its just what ive read on here this last wk or so.

Any global drivers remain of little anticipated influence into medium range (as previously outlined). MJO expected to remain weak in W Pacific, with only a minority of ENS yielding sufficient amplitude to be of predictive value for UK weather. Signal for a significant SSW mid-Feb remains a minority in latest output. Despite expected eastwards shunt of the cold vortex, cold/rather cold boundary layer across UK won't necessarily budge as willingly under anticyclonic conditions (when they arrive). Despite lack of clear global drivers and (currently) only minority cluster signal for major SSW, there remains tentative signs of a generally more blocked/anticyclonic/drier/colder boundary layer regime later Feb, as more simply expressed in UKMO 16-30D forecast.

[West is Best]

You'd think looking at the models that there was now good, nailed on, agreement for the end of this (frankly pale and miserable) cold spell. All three models prog the toppler high mid week with warm uppers slowly building from the north, leading to the possibility of inversion: cold at the bottom and warmer at the top. Much on that will depend on whether the high is 'dirty,' as we've frequently seen at this time of year, especially after the damp ground from all this rain, sleet and slushy mix.

 

However, for those who would like to see the current setup continue or perhaps improve the GEFS ensembles continue to hold out some hope. The operationals are on the mild side, with many colder members:

 

 

However, the fact that the three operationals from GFS, ECM and UKMO go for the midweek toppler high makes the colder members probably around a 10% chance, maybe less.

 

Looking ahead there's now a significant potential problem. Many of us look to blocking for proper cold to occur, and blocked signals are pounced upon. Over the last 20 years we've seen February and March become ideal times for this as the jet, typically, abates. Unfortunately if the blocking is in the wrong place that's not so great. This high that is building over the UK this week has the potential to stick around for a long time, either over us or just to our east. The winter clock could be ticking.

Edited February 1, 2015 by West is Best

[KTtom]

Any global drivers remain of little anticipated influence into medium range (as previously outlined). MJO expected to remain weak in W Pacific, with only a minority of ENS yielding sufficient amplitude to be of predictive value for UK weather. Signal for a significant SSW mid-Feb remains a minority in latest output. Despite expected eastwards shunt of the cold vortex, cold/rather cold boundary layer across UK won't necessarily budge as willingly under anticyclonic conditions (when they arrive). Despite lack of clear global drivers and (currently) only minority cluster signal for major SSW, there remains tentative signs of a generally more blocked/anticyclonic/drier/colder boundary layer regime later Feb, as more simply expressed in UKMO 16-30D forecast.

 

Also interesting to read the 6-15 day forecast does not back the mid range GFS by mentioning Atlantic influence and unsettled conditions where as the GFS has anticyclonic conditions in charge for the foreseeable..

[knocker]

You'd think looking at the models that there was now good, nailed on, agreement for the end of this (frankly pale and miserable) cold spell. All three models prog the toppler high mid week with warm uppers slowly building from the north, leading to the possibility of inversion: cold at the bottom and warmer at the top. Much on that will depend on whether the high is 'dirty,' as we've frequently seen at this time of year, especially after the damp ground from all this rain, sleet and slushy mix.

 

However, for those who would like to see the current setup continue or perhaps improve the GEFS ensembles continue to hold out some hope. The operationals are on the mild side, with many colder members:

 

Screen Shot 2015-02-01 at 08.06.47.png

 

However, the fact that the three operationals from GFS, ECM and UKMO go for the midweek toppler high makes the colder members probably around a 10% chance, maybe less.

 

Not too sure what you mean by "with warm uppers slowly building from the north, leading to the possibility of inversion: cold at the bottom and warmer at the top" WiB. The 'warm' uppers in the anticyclone are caused by the subsiding air which warms as it descends. It doesn't descend to the surface but stops in the lower trop where you get the inversion at the boundary of the cold and warm air. The level at which you often get the formation of Stratocumulus and gloom. On a skew-t you would have a sharp lapse from the surface to the base of the inversion with dew points rising to dry bulb level (saturated air) and then a very rapid decrease of dew point in the dry warmer air above the cloud (if there is any).

Edited February 1, 2015 by knocker

[TEITS]

Just adding to Nicks post

 

the UKMO break point of that low

 

http://www.meteociel.fr/ukmo/runs/2015020100/UN144-21.GIF?01-06

 

is considerably further west than the ECM

 

http://www.meteociel.fr/modeles/ecmwf/runs/2015020100/ECH1-144.GIF?01-12

 

 

The polar vortex dropping like I said like last night is still just coming into UKMO range.

 

Thats the key peice to keep an eye on today as was mentioned last night.

 

I simply stated I cannot see the upgrades you were referring to and this mornings operationals continue to suggest HP centred across the UK or just centred W. I can see what you mean though looking at the UKMO but even if the models are too far W the PV continues to be modelled over Greenland.

 

The GEFS ensembles are now beginning to trend towards the Ops as less bitterly cold runs are on the 0Z set and the mean has risen by a few degrees.

http://max.nwstatic.co.uk/ensimages/ens.20150201/00/t850Cambridgeshire.png

 

So in summary yes the models could shift W and we do see a very cold N,ly on the right flank of the HP. However at the moment the evidence suggests this will occur much further E into Europe.

Edited February 1, 2015 by Osbourne One-Nil
Line you referred to been removed from quoted post.

[bluearmy]

There is some spread support for those lower heights and uppers to get close to our east and se by day 8. Whilst the spread shows it, can't be discounted.

.

[johnholmes]

The EC-GFS anomaly output this morning, link below, is pretty similar on both to the NOAA 6-10 last evening. What some are suggesting might happen is a possibility but the overall upper air evidence in the 6-10 day time frame does not suggest this being very lijkely. So high pressure dominated with surface cold not deep upper air cold seems the best bet to me.

http://mp1.met.psu.edu/~fxg1/ECMWF_0z/hgtcomp.html

Edited February 1, 2015 by johnholmes

[JoeShmoe]

A winter anticyclone now looking the form horse with associated 'faux cold' - we've seen these in previous years hang about for several weeks and as has been said clock is ticking

Striking things has again been no sign of HLB this winter, in many ways feel we've been quite lucky to have gotten the cold PM flow we have

[mushymanrob]

Or Stratocumulus gloom Mushy. Mind if Nick is going for hard frosts that would probably rule it out.

 

i heed what nick says which is why i asked the question. i see you too think that its likely to be a 'dirty high'.  heres why

as winds drop out later in the week, with temps cold but above freezing by day, there will be some snow melt, clear skies at night, fog could become an issue. this often lifts to low cloud over a several day period.

secondly, your description of the inversion creating cloud is better interpreted then i could, but i agree with it which (from experience, not science) i thought it would be a 'stratfest' yesterday.

thirdly ... the position of the high

thats a long seabound track for cold continental air crossing the reletively warm atlantic, before its returned to cross us in the circulation of the high. that smacks of it being a dirty high...

and fourthly

 

theres an old embedded front heading slowly south on the eastern flank of the high... that would introduce cloud.

 

so whilst the mild southwesterlies might be gone (for now at least), this high is looking like a chilly gloom fest, not a clear bright cold frosty one. as things stand. whilst temps will be below average, in the calm air itll be very useable for outdoor activities, and its looking dry!

further ahead and its still looking like it MIGHT become mild, the ops are showing more likelyhood of this then any snowy cold spell. i dare say i could find ens support from a few members for this too if i bothered! lol

 

[IDO]

Just adding to Nicks post

 

the UKMO break point of that low

 

http://www.meteociel.fr/ukmo/runs/2015020100/UN144-21.GIF?01-06

 

is considerably further west than the ECM

 

http://www.meteociel.fr/modeles/ecmwf/runs/2015020100/ECH1-144.GIF?01-12

 

 

The polar vortex dropping like I said like last night is still just coming into UKMO range.

 

Thats the key peice to keep an eye on today as was mentioned last night.

 

Yes I think we cannot discount the HP sitting further west and lower heights falling to the eastern side of the UK. The GEM Control highlights this:

 

 

 

It has 15-20% support amongst its ensembles and the GEFS are similar (10-15%):

 

 

Unlikely though and as we don't see the UKMO ensembles it is difficult to know where it sits. However Ian F has tweeted that HP looks like it is in charge for the first half of Feb, so I suspect the UKMO op is also sitting in a small cluster.

 

The GFS op has been a mild outlier for the last 2-3 days (0z) and has slowly been dragging its ensembles in that direction:

 

 

The most likely scenario is that HP will settle over the UK for 5-7 days from Thursday. As the models are just resolving this period it is probably not much help looking for what happens after that (mid Feb onwards). Looking through FI GEFS and there is no clear signal yet that the PV will go into low amplitude mode and maybe the shenanigans in November have just meant that the PV's dominance now extends into Feb rather than waning. Certainly all the expectations from that initial November meridional flow have busted and it could be that the effect of that period is to dampen the usual correlations? This current "cold" spell has mainly been on the wrong side of marginal for the south so just ordinary January weather in reality so we really need major developments in the NH if we are going to get a noteworthy cold spell in Feb. Nothing is close to hinting at that yet (still time though).

[SussexmarkyMark]

I don't post on here very often these days, because my technical knowledge is not sufficient to enter into conversations with those who use complex reasoning to justify why they believe certain outcomes are more likely.  I prefer to look at charts in a more simplistic way which often seems to be the best way to see what the most likely outcome is.  Whilst many have used the charts to justify talk of unstable northerlies, complex features and polar lows, bringing the risk of heavy snow and not just the 'wishbone' effect, with very low temperatures, the more simplistic view suggested that for many this wintery spell would not bring anything significant.  For many over a large swathe of Southern England, we're still waiting for the bitterly cold weather to kick in.  Firstly we were told it was going to happen on Thursday - temperatures were around 5 or 6 in many areas - then we were told it's going to be Sunday - here are today's forecast maxima from GFS:

 

 

Once the cold is 'set in', the forecast maxima are as follows:

 

 

And then we have this for the end of the week:

 

 

So, this chilly period of weather, initially accentuated by the wind, remains pretty much as it is now for many areas, and there doesn't seem much chance of any significant snowfall either.  I'm sure further north it has been colder and there has been lying snow, although how much to widespread low-lying areas, I don't know,  and indeed there has been the occasional light covering down here, but if overnight snow, doesn't even make it to lunchtime, with daytime temperatures of 4 or 5c, it's hardly a major cold event and the outlook for this coming week just looks like more of the same to me

Edited February 1, 2015 by SussexmarkyMark

[West is Best]

Not too sure what you mean by "with warm uppers slowly building from the north, leading to the possibility of inversion: cold at the bottom and warmer at the top" WiB. The 'warm' uppers in the anticyclone are caused by the subsiding air which warms as it descends. It doesn't descend to the surface but stops in the lower trop where you get the inversion at the boundary of the cold and warm air. The level at which you often get the formation of Stratocumulus and gloom. On a skew-t you would have a sharp lapse from the surface to the base of the inversion with dew points rising to dry bulb level (saturated air) and then a very rapid decrease of dew point in the dry warmer air above the cloud (if there is any).

 

Sorry if I raised a non-sequitur there and you're right it was a casual remark. I meant that if the moisture at the surface is trapped under the high with warmer 850hPa's above then temperature inversion is likely, that's all. You do not, correct me if I'm wrong, so often see inversion under bone-chilling 850hPa's and dry ground? To cut to the chase, with projected uppers from this toppler high rising above 0C, as opposed to, say, -10C, given the ground conditions inversion is more likely. No?

Edited February 1, 2015 by West is Best

[Gibby]

Sorry rather late this morning but better late than never.

HERE IS MY LATEST ANALYSIS USING DATA SUPPLIED BY THE NWP OUTPUT COVERING 5 OF THE WORLDS MOST POWERFUL WEATHER COMPUTERS

THE CURRENT GENERAL SITUATION A cold Northerly flow will continue across the UK with minor disturbances in the flow gradually clearing away South.

MODELS-2 WEEK HEADLINE Remaining cold with some snow showers especially near northern coasts. Becoming dry and possibly less cold in the North later.

THE JET STREAM ENSEMBLE FORECAST The Jet Stream Forecast shows the deep trough in the flow across Europe currently remaining for another week or so before signs of the trough lifting out somewhat to a WNW to ESE flow just South of the UK later in the period.

GFS OPERATIONAL The GFS operational today shows cold North and then NE for much of the UK over this coming week as further disturbances run South across the UK on Tuesday with another mix of rain and snow followed by a veer of wind to NE as pressure builds in from the west cutting off the cold feed from all but South and East England next weekend. The weather will stay cold and anticyclonic as High pressure sits over or near the UK from day 6-10 before the High collapses slowly SE and allows less cold Westerly winds to move in across many areas at least for a time at the end of the period.

THE GFS CONTROL The GFS control run is in many ways a replica of the operational in theme with just differences in speed and extent of the breakdown away from High pressure in Week 2 with only a slow pick up in temperatures more likely for the North and West in the largely dry pattern of weather.

THE GFS CLUSTERS The GFS Clusters show a 65%/35% split in favour of an Anticyclone lying near or over the UK in 14 days time giving rise to dry and fine if cold conditions with frosts at night. The remaining 35% go for a more Atlantic type pattern with Low pressure to the North or NE in West or NW winds.

UKMO UKMO this morning shows High pressure building in from the West through the latter stages of this week with the NE feed across the South weakening by next weekend as a ridge of High pressure lies across the UK with fine and frosty conditions replacing the snow showers of the late working week. From the Day 6 chart High pressure to the west looks like setting up to deliver a further push of cold air from the North in the following week..

THE FAX CHARTS The Fax Charts show a slow build of pressure through the week as an Atlantic High becomes more dominant. The precursor to that will be a series of weak disturbances running South at times giving rise to patchy rain and sleet and snow showers on the temporary NE feed in the second part of the week for the South and East.

GEM GEM today shows High pressure gradually taking control of the weather as we move through the latter part of this week as a ridge extends East from it across the UK sinking South later cutting off the cold NE feed and snow showers with little wind and cold frosty conditions. Then the High recedes back out into the Atlantic towards the SW and sets up a benign WNW airflow with gradually rising temperatures and rather cloudy but dry conditions for many for the start of week 2.

NAVGEM NAVGEM today keeps the Northerly then NE feed going throughout the first 4 days of the working week with snow showers in the East before High pressure takes control centred over Scotland next weekend with quiet and settled conditions with sharp frosts and freezing fog patches likely but compensatory sunny days.

ECM ECM this morning also shows High pressure becoming the dominant feature of the UK weather over the period once we lose the Cold and unstable North and NE airflow over the UK until later in the week. The High then sets up residence across the UK with very frosty nights but bright, cold but sunny days for many.

ECM 10 DAY MEAN The 10 Day Mean this morning indicates the likelihood of High pressure lying over or close to the UK in 10 days time with fine and settled weather. The coldest weather is likely in the South as some members show a milder westerly flow over the North.

NOTABLE TREND CHANGES FROM PREVIOUS RUNS The trend has gained universal support from the models for High pressure to replace the current cold Northerly flow later next week and beyond. The resting place of such a High is yet to be determined.

MY THOUGHTS The cold spell continues across the UK and though for many I'm sure it is nothing more than slightly below par period of temperatures with little in the way of frost as yet some areas have at least seen some snowfall and this pattern is set to continue for some days yet with maybe some new areas who have yet to see snow at risk of at least a little, principally from Tuesday to Thursday as a disturbance runs South over the UK veering the North wind to NE opening the door for the East and SE to run the risk of snow showers. After Tuesday the risk of snow in the SW is minimal and in any event there is now almost universal support for High pressure to ridge in across the UK from the West, certainly by next weekend cutting off any remaining NE flow and settling the weather down to a typical Winter Anticyclone type with overnight sharp frosts and freezing fog patches with bright and sunny days and in these the South will feel quite pleasant in the near calm conditions and rising sun elevation. It's then that the differences in evolution between the models become apparent but not in any particularly dynamic sort of way. Most models want to move High pressure away from the UK in week 2 with the UKMO looking to pull it West and perhaps set up a new Northerly later. ECM holds it firm across the UK with quite a lot of support from it's ensemble members from it's own group and GFS too. What isn't shown is any type of Easterly flow developing nor a raging Atlantic westerly either so the odds on favourite is that after this weeks sleet and snow showers finally give way then the rest of the period looks dry and fine but rather cold by day and very cold by night with frost and freezing fog patches especially over any still remaining lying snow by then.

Issued at 08:00 Sunday February 1st 2015

[shaky]

Hmmm low disrupting in the north sea at 96 hours on gfs 06z!! Wasn't there over the past few runs so keep an eye on it!! Might pull in colder uppers for a time!!

[shaky]

big changes at 114 hours!! High further north and now we got bitterly cold -10 850s coming into east anglia! !

[seabreeze86]

The 6z might raise a few eyebrows, high pushing further north allowing a better easterly for a time one to watch.

 

http://modeles.meteociel.fr/modeles/gfs/runs/2015020106/gfs-0-114.png?6

[Gowon]

Hmmm low disrupting in the north sea at 96 hours on gfs 06z!! Wasn't there over the past few runs so keep an eye on it!! Might pull in colder uppers for a time!!

 

Yeah it certainly looks better

 

[Ice Day]

Well, well ,well.  126 and an easterly's showing with decently chilly uppers.