Model output discussion - 20th Feb onwards

[Weather Observer]

I share the frustration of most coldies that this latest SSW is not looking like it will deliver the last wintery blast . However, all is not lost yet, and just to remind us of what that would look like ..........

Also as a fellow New Forester now living away,  I would ask Singularity not to worry  too much about the wildlife. It is more adaptable than we are. I feel we are the problem for wildlife rather than the weather.

 

[nick sussex]

18 minutes ago, Singularity said:

Thanks for your take on things Phil 

I'm aware of the lack of propagation down but that's just the thing - for a SSW that splits the vortex clean in two, there really should be propagation right down to the troposphere and at a fair old pace too. Unless, of course, the theory I have read through is not entirely correct or has overlooked possible exceptions to the rule. On the other hand, Fergie has mentioned the issues with models struggling to handle the SSW (though the latest such advice was a few days back I think) and past experience does suggest that for whatever reason, the propagation mechanism is something the models have a hard time capturing effectively.

The actual outcome this month will have major ramifications in terms of how far the models have progressed since the last major SSW in 2009.

 

Edit: @knocker just wanted to check, is this an accidental contradiction in your post? "GEFS building heights south of Greenland thus veering the wind. Thus the weather turning more unsettled and the temps returning to around average"

tia.

Could the lack of propagation down be related to the state of the AO at the time of the SSW. The research paper into that suggested the strongest trop response was with the AO in positive territory, this less evident at neutral and even less so if the AO was negative.

It would of course sum up the year so far if one of the strongest zonal reversals still didn't deliver a higher latitude block.

Edited March 8, 2016 by nick sussex

[phil nw.]

7 minutes ago, Singularity said:

Thanks for your take on things Phil 

I'm aware of the lack of propagation down but that's just the thing - for a SSW that splits the vortex clean in two, there really should be propagation right down to the troposphere and at a fair old pace too. Unless, of course, the theory I have read through is not entirely correct or has overlooked possible exceptions to the rule. On the other hand, Fergie has mentioned the issues with models struggling to handle the SSW (though the latest such advice was a few days back I think) and past experience does suggest that for whatever reason, the propagation mechanism is something the models have a hard time capturing effectively.

The actual outcome this month will have major ramifications in terms of how far the models have progressed since the last major SSW in 2009.

 

Edit: @knocker just wanted to check, is this an accidental contradiction in your post? "GEFS building heights south of Greenland thus veering the wind. Thus the weather turning more unsettled and the temps returning to around average"

tia.

Cheers S.

Yes i noted in some of your recent posts regarding the lack of tropospheric response-my post was just to illustrate this really through the use of the models prompted by my own curiosity.

I don't know why the complete down welling hasn't yet shown and maybe this is something  that will still happen but in stages and not in one event.I would think pretty soon we would be looking at a final warming anyway as the polar night is virtually at end so any vortex recovery would be short-lived.

Interesting though to follow how the final throes of the pv impacts on our 500hPa pattern as i can't recall so much discussion on this facet of model output discussion in previous years.

I guess it shows how the quest for more understanding has grown and spread to forums such as this.Keep up the good work on here.

[wishingforsnow]

After a bit of a break from this forum (model watching fatigue I have to admit!)  my take on the SSW is that at least it could deliver a less extreme version of March 2013 and at best a replica of March-April 2013. At least the predominantely unsettled weather day in and day out has finally hit the road after nigh on 4 months plaguing the UK as it now looks more likely according to models that a much needed settled, chiller period could be on the cards which is just what we need to dry ourselves out after the second wettest winter on record  The Atlantic and PV also does not have as much power as it did 1-3 months ago so any Atlantic wet weather should not last as long as it did in Winter perhaps the odd unsettled days but unlikely to be weeks of rain and wind again. 

Edited March 8, 2016 by wishingforsnow

[Nouska]

1 hour ago, Singularity said:

The actual outcome this month will have major ramifications in terms of how far the models have progressed since the last major SSW in 2009.

We had another couple of SSWs since 2009  - February 2010 and January 2013. The last one certainly propagated down swiftly and had a lasting and memorable effect - well captured in the modelling. This event just maybe delayed or there is something else going on which is not being factored in.

I posted a paper in the Strat. thread which, I think, outlines the progression of this winter well. No strength to Wave 2 and is in fact an overlap in Wave 1 that actually interferes with midwinter SSW development.

 

[Walsall Wood Snow]

I know despite the SSW, that a cold spell as major as the last third of March 2013 is looking unlikely. But surely we could still get a snow day (perhaps even a blizzard) if things fall into place. After all we had settling snow in the night (though the Sun got to work on it the next day) in April 2008. There are of course examples of snow occurring in April in other years such as 1981 and 1989 and not to mention as late as June in 1975 (though that was an extreme anomaly). What's interesting though that all those examples (with the exception of 1981) occurred following mild or very mild Winters (not that I'm suggesting they occurred because of that, just that its obviously not impossible for such to happen despite that).

[knocker]

2 hours ago, Singularity said:

Thanks for your take on things Phil 

I'm aware of the lack of propagation down but that's just the thing - for a SSW that splits the vortex clean in two, there really should be propagation right down to the troposphere and at a fair old pace too. Unless, of course, the theory I have read through is not entirely correct or has overlooked possible exceptions to the rule. On the other hand, Fergie has mentioned the issues with models struggling to handle the SSW (though the latest such advice was a few days back I think) and past experience does suggest that for whatever reason, the propagation mechanism is something the models have a hard time capturing effectively.

The actual outcome this month will have major ramifications in terms of how far the models have progressed since the last major SSW in 2009.

 

Edit: @knocker just wanted to check, is this an accidental contradiction in your post? "GEFS building heights south of Greenland thus veering the wind. Thus the weather turning more unsettled and the temps returning to around average"

tia.

No. Why is it a contradiction? Flow becoming NW.

Edited March 8, 2016 by knocker

[Speedway Slider]

What was the 1975 June anomaly?

[Singularity]

1 minute ago, knocker said:

No. Why is it a contradiction? Flow becoming NW.

Oh do you mean to the south of Greenland i.e. a mid-Atlantic high? In which case I see the logic.

 

Interesting thoughts on the impacts of the AO state on the SSW @nick sussex, I had been thinking that a neutral or positive precursor AO is sufficient for a significant impact, but it could be that the ill-defined nature of a neutral AO interferes the propagation down and leads to a messier picture in the troposphere, with a more hit-and-miss result at the mid-latitudes.

There was just a hint of zonal reversal right down to the surface in yesterday's ECM strat. output, but it was up near 80*N and quickly lost again:

 

There is a real struggle to remove the 1000-100 hPa zonal winds at the lower latitudes (around 60*N). Proof that size isn't everything when it comes to a SSW event.

[TomDav]

Looks like there will be potentially quite a potent northerly / north westerly flow around D15

[Walsall Wood Snow]

23 minutes ago, Speedway Slider said:

What was the 1975 June anomaly?

When it snowed then.

[fergieweather]

23 minutes ago, Singularity said:

There was just a hint of zonal reversal right down to the surface in yesterday's ECM strat. output, but it was up near 80*N and quickly lost again:

 

There is a real struggle to remove the 1000-100 hPa zonal winds at the lower latitudes (around 60*N). Proof that size isn't everything when it comes to a SSW event.

Indeed. You might recall how a few days ago I mentioned how GloSea5 wasn't wholly convincing on whether easterlies would propogate right down; whilst the reversal aloft has been clear-cut (eg see recent GloSea5 strat diagnostics below; I can't show latest version), the tropospheric effects remain less immediately tangible. Latest thinking is that whilst SSW hasn't incepted the HP story emerging by this weekend (= too short lead time), it does probably result in its apparent longevity. That is in itself still an imponderable, as (per previous posts), the ongoing signal for a return to lowering GPH and increasing cyclonicity post-21st *may* be too fast (models always tend to overcome blocking too readily)...but nonetheless, that outcome remains a clear and arguably growing possibility, given repeating ENS signs of such, including 12z EC-EPS.

Edited March 8, 2016 by fergieweather

[Speedway Slider]

12 minutes ago, Walsall Wood Snow said:

When it snowed then.

Yes, sorry, didn't ask this well at all! What was the anomaly that caused the snow in June...?

[knocker]

The points of note vis this morning's GFS is the shifting of the upper high further east which will depress the expected high temps a tad and the speed with which this breaks down. This scenario is supported by the GEFS anomalies.  They have the Atlantic trough moving east as the HP breaks down which initially brings a relative warm SW flow but as pressure rises in mid Atlantic this veers to NW as the trough settles over the UK. Thus a swing from temps above average to probably a little below as more unsettled weather becomes the order of the day. This is very much in line with the EC32. Easter cooler and unsettled.  The main trough and the colder air remains ensconced over NE Europe.

 

Edited March 9, 2016 by knocker

[winterof79]

The ECM showing the retrogression of the locked up cold as the run lengthens

 

 

[Interitus]

8 hours ago, Nouska said:

We had another couple of SSWs since 2009  - February 2010 and January 2013. The last one certainly propagated down swiftly and had a lasting and memorable effect - well captured in the modelling. This event just maybe delayed or there is something else going on which is not being factored in.

I posted a paper in the Strat. thread which, I think, outlines the progression of this winter well. No strength to Wave 2 and is in fact an overlap in Wave 1 that actually interferes with midwinter SSW development.

 

Yes as pointed out in the strat thread, wave 2 has been very weak this winter -

Though there is some vortex splitting forecast, it is not unusual for daughter vortices to form during/following a displacement which causes confusion when classifying SSW type as seen in this table from Charlton & Polvani -

But the current splitting is not by the classical wave 2 forcing and it may be that the underlying forcing mechanism helps determine how quickly and effectively the SSW downwells - a strong trop/strat wave 2 would be predisposed to a split vortex.

[Gibby]

HERE IS MY LATEST ANALYSIS USING DATA SUPPLIED BY THE NWP OUTPUT COVERING 5 OF THE WORLDS MOST POWERFUL WEATHER COMPUTERS ISSUED AT 09:00 ON WEDNESDAY MAR 9TH 2016

THE CURRENT GENERAL SITUATION A deep Low pressure across Southern England will move away SE across France later today and tonight with an occluded front across Central areas dissipating by tomorrow as pressure rises strongly across the UK under a ridge of High pressure.

http://www.wetterzentrale.de/pics/Rtavn001.gif

CURRENT SNOW FORECAST AND FREEZING LEVEL OVER THE UK The freezing level across the UK will be a little higher than recently at around 3000ft over the next few days before rising slowly from the West and NW over the coming days. Snowfall will be restricted to the highest hills of England and Wales for a time today.

http://www.snow-forecast.com/maps/dynamic/uk

http://www.natice.noaa.gov/pub/ims/ims_gif/DATA/cursnow.gif

MODELS-2 WEEK HEADLINE  Becoming less cold and mostly dry but perhaps turning rather colder again later with frost at night.

THE GFS JET STREAM FORECAST  The Jet Stream is currently about to change it's orientation to a position NW of the UK and moving in a NE direction as pressure builds across the UK. Then as we go through the weekend and next week the Southern arm of the flow becomes stronger and moves North to become the main flow by then crossing West to East over the UK. Finally towards the end of the period the flow becomes much more unclear in both positioning and strength. 

http://www.netweather.tv/index.cgi?action=jetstream

GFS OPERATIONAL The GFS Operational Run today shows pressure rising across the UK over the next few days as Low pressure over the South subsides away South. A belt of High pressure then lies across Southern Britain by the weekend while the North sees milder SW winds and all areas will feel the benefit of milder air for a time. However as High pressure shifts further North showery rain will be pushed NE across England and Wales as a SE to east flow develops. Then it'a all about the return of more changeable weather across the British isels in a Westerly flow by the end of the period.

GFS CONTROL RUN The theme of the Control Run shows a very similar trend to the Operational again this morning with the exception of colder conditions shown sweeping South across the UK again towards the end of the second week as High pressure to the West spreads wintry showery South with frosts at night. 

http://www.wetterzentrale.de/pics/Rtavn1441.gif

http://www.wetterzentrale.de/pics/Rtavn3841.gif

http://www.meteociel.fr/modeles/gefs_cartes.php?code=0&ech=144&mode=0&carte=0

http://www.meteociel.fr/modeles/gefs_cartes.php?code=0&ech=384&mode=0&carte=0

GFS ENSEMBLE DAY 14 DATA  The GFS Clusters once again today look very undecided on what the UK will lie under in two weeks time as all sorts of options are shown ranging from Low pressure across the UK with rain at times and much slacker pressure areas with benign weather neither fine nor wet.

http://www.weatheronline.co.uk/cgi-bin/expertcharts?LANG=en&MENU=0000000000&CONT=euro&MODELL=gefs&MODELLTYP=2&BASE=-&VAR=cpre&HH=372&ZOOM=0&ARCHIV=0&RES=0&WMO=&PERIOD=

UKMO The UKMO model this morning shows High pressure building across Southern Britain in the next few days and extending slowly North later as it rests over the North Sea. Milder air will engulf the UK for a while before temperatures ease back a little in the South later as an ESE breeze develops here. 

http://www.wetterzentrale.de/pics/Rukm1441.gif

THE FAX CHARTS From the Fax Charts this morning it would appear that substantially mild air is going to struggle to get down across the Southeast of the UK as a warm front introducing it straddles the middle of the UK over the weekend. So while the North and West become milder with some rain at times in the far NW the South and East look like staying dry if cloudy and somewhat cooler than originally thought.

http://www.weathercharts.org/ukmomslp.htm#t120

GEM GEM this morning maintains it's High pressure based predictions with the High centre mostly to the East or NE but never drifting far away from our shores. The weather will be benign for the most part with varying amounts of cloud and some sunshine and temperatures probably ending up close to average but with some night frosts at night. There are signs at the very end of the run that the High may be slipping away SE allowing Atlantic fronts into the NW.

http://www.wetterzentrale.de/pics/Rgem2401.gif

NAVGEM NAVGEM looks very high pressure focused too with the centre gradually extending as a belt across Southern Britain and nearby Europe to a migration somewhat further North later displacing the cloudy, damp and mild SW flow in the NW up to the weekend. Fine and settled conditions prevail for many with temperatures close to normal and the risk of some frosts at night should skies clear.

http://www.wetterzentrale.de/pics/Rnvg1681.gif

ECM ECM today is a very settled one again with High pressure extending across Southern Britain in the next few days time and then extending to all of Britain over the weekend and beyond as the High centre drifts further North. Some bright Spring sunshine looks very likely for many with some frosts at night but temperatures by day would be close to average overall and perhaps quite mild at first. 

http://www.wetterzentrale.de/pics/Recm2401.gif

ECM 10 DAY MEAN The 240hr mean Chart this morning continues to project a High pressure ridge likely to be lying across the UK in 10 days with fine and settled conditions in light winds most probable.

http://www.wetterzentrale.de/pics/Reem2401.gif

NOTABLE TRENDS & CHANGES FROM PREVIOUS RUNS The trend is well set for the weather to become fine, settled and less cold from the latter end of the week with solid cross model support for High pressure to build across or remain close to the UK.

31 DAY HISTORICAL VERIFICATION STATS FOR GFS, UKMO & ECM The verification Statistics of GFS, UKMO and ECM show at 24 hours ECM ahead at 99.6 pts with UKMO at 99.5 pts and GFS at 99.4 pts.  At 3 days ECM is leading with 97.7 pts to UKMO's 97.1 pts while GFS lags behind at 96.3 pts. At 5 days ECM leads with 91.2 pts to UKMO at 89.3 pts and GFS at 86.7 pts. Then at 8 Days ECM has the leading spot from GFS with 66.0 pts to 61.2 pts. Finally at Day 10 ECM has regained the lead from GFS with a score of 46.3 pts to 46.2 pts.

http://www.emc.ncep.noaa.gov/gmb/STATS_vsdb/allmodel/daily/cor/cor_day1_PMSL_MSL_G2NHX.png

http://www.emc.ncep.noaa.gov/gmb/STATS_vsdb/allmodel/daily/cor/cor_day3_PMSL_MSL_G2NHX.png

http://www.emc.ncep.noaa.gov/gmb/STATS_vsdb/allmodel/daily/cor/cor_day5_PMSL_MSL_G2NHX.png

http://www.emc.ncep.noaa.gov/gmb/STATS_vsdb/allmodel/daily/cor/cor_day8_PMSL_MSL_G2NHX.png

http://www.emc.ncep.noaa.gov/gmb/STATS_vsdb/allmodel/daily/cor/cor_day10_PMSL_MSL_G2NHX.png

MY THOUGHTS  This morning continues to project a change in the weather over the coming few days and then lasting for some considerable time. In the meantime we still have to get rid of this nasty Low pressure across Southern Britain this morning with it's attendant gales and heavy rain but once passed it looks like this could be the last heavy rain and strong winds we see in the South for quite a time. The orientation of the anticipated High pressure has changed somewhat over the last day or so and it now looks as if the High will lie in a belt across the South come the weekend with the mild Atlantic SW'lies affecting the North and West with a little rain at times here whereas in the South quiet and benign weather conditions will bring slightly colder air than first though here though it could hardly be described as cold. then as we move out of the weekend and through next week it looks like High pressure will extend across all of Britain with fine and settled weather with some sunshine by day and frosts where skies clear at night. Temperatures by day should be close to average and this might mean they fall back somewhat to levels expected at the weekend across the NW. With regard to the longevity of the spell the jury is out as a cocktail of synoptics from all models are shown for two weeks time offering no clues. however, there doesn't look to be anything alarmist to worry about within the next few weeks so let's sit back and enjoy a much welcome dry and fine period and with a bit of luck the strengthening sunshine at this time of year should signify thoughts that Spring proper is only just around the corner.

Next Update Thursday March 10th 2016 from 09:00

[MP-R]

Quite an interesting run from the GFS 00Z with something for everyone really.

Where we are now with this potent low moving through but clearing to the east as the day goes on. Looks like the dregs will hang around tomorrow with a largely dull day for most before improving Friday onwards with a little bit more in the way of sunshine, but certainly not a spring fest.

Never really becoming that warm before the cool easterly sets in early next week. Could feel quite raw depending on cloud amounts. Wedge of -5 uppers crossing the country.

A matter of days later winds veer southerly bringing up milder air (Spanish plume anyone?)

Then normal March fare resuming in FI. 

It's pretty nailed that a dry spell of probably about 10 days is coming though I doubt it will feel that impressively springlike with a nagging breeze across the south especially, better further north. What will make the difference is the amount of sunshine. I think there's been a signal for a less anticyclonic final third to the month. That will need monitoring as we get nearer the time.

[knocker]

The ecm 5-10 is as expected and really it will boil down to the precise orientation of the upper high. Moving along the ext EPS follows a not dissimilar route to the GEFS with the UK HP initially ridging towards Iceland with a weak trough edging east. This eventually ends up with ridging mid Atlantic and a weak trough over the UK and a NW flow; ergo weather more unsettled with temps a little below average. The main trough and colder air still situated NE Europe.

I think the Easter barby might have to be in the woodshed.

Edited March 9, 2016 by knocker

[KyleHenry]

It's all just a waiting game, we know the science and what should occur from atmospheric processes. 

Within next 7 days GFS has Trop PV moving to Siberia. It leaves an opening for heights to gain access to Greenland.

If so, how far westward will the cold pool get? 

The cold is there. 

Edited March 9, 2016 by KyleHenry

[Singularity]

The latest det. runs certainly indicate that the axis of cold export from the Arctic may fall just a little too far east to hit us directly. A typical story and one that threatens to bring us weather that is merely chilly, grey and unpleasant.

A shift either east or west improves our fortunes one way or another; the former in terms of more springlike weather, the latter for a late blast of wintry weather with snow a prominent feature. So who's betting we get that no-mans-land instead 

At least it looks to be largely dry for a long time, perhaps very long if we assume GFS' attempts to return zonality beyond day 9/10 are a result of model bias as opposed to a probable outcome.

 

  

This GEFS mean leans toward the pattern evolving far east enough that we could even find ourselves on the side where warm air is flooding north as the counterpart to the cold air flooding south into western Asia/eastern Europe. EC ens. mean is similar and then even suggests a SW flow being possible.

I'm not convinced that the Atlantic trough will find that much westerly momentum, however. The EC spread shows uncertainty to our east that reflects the potential for the Siberian trough to move closer, and uncertainty to west which suggests the Atlantic trough could be either nearer still (somehow!) or further away to the west.

I do wonder if what we're seeing is the propagation down of the SSW stuttering a bit due to the neutral AO state, this preventing the fast-moving vortex remnant moving S of the UK and then W across the Atlantic from achieving much in the troposphere, while the near-stationary vortex remnant over Siberia is able to drive the trop. pattern due to its persistence in that area.

A possible adjustment to watch out for is the vortex remnant near us ending up further south, with the polar jet following suit. That increases the odds of an undercut from the Atlantic trough, with the UK high heading NW. This does however lead me to expect a fairly brief spell of notable cold followed something fairly benign as the main blocking moves away but we have only a fairly weak jet stream to drive low pressure systems our way. Just speculation, mind!

[feb1991blizzard]

30 minutes ago, Singularity said:

The latest det. runs certainly indicate that the axis of cold export from the Arctic may fall just a little too far east to hit us directly. A typical story and one that threatens to bring us weather that is merely chilly, grey and unpleasant.

A shift either east or west improves our fortunes one way or another; the former in terms of more springlike weather, the latter for a late blast of wintry weather with snow a prominent feature. So who's betting we get that no-mans-land instead 

At least it looks to be largely dry for a long time, perhaps very long if we assume GFS' attempts to return zonality beyond day 9/10 are a result of model bias as opposed to a probable outcome.

 

  

This GEFS mean leans toward the pattern evolving far east enough that we could even find ourselves on the side where warm air is flooding north as the counterpart to the cold air flooding south into western Asia/eastern Europe. EC ens. mean is similar and then even suggests a SW flow being possible.

I'm not convinced that the Atlantic trough will find that much westerly momentum, however. The EC spread shows uncertainty to our east that reflects the potential for the Siberian trough to move closer, and uncertainty to west which suggests the Atlantic trough could be either nearer still (somehow!) or further away to the west.

I do wonder if what we're seeing is the propagation down of the SSW stuttering a bit due to the neutral AO state, this preventing the fast-moving vortex remnant moving S of the UK and then W across the Atlantic from achieving much in the troposphere, while the near-stationary vortex remnant over Siberia is able to drive the trop. pattern due to its persistence in that area.

A possible adjustment to watch out for is the vortex remnant near us ending up further south, with the polar jet following suit. That increases the odds of an undercut from the Atlantic trough, with the UK high heading NW. This does however lead me to expect a fairly brief spell of notable cold followed something fairly benign as the main blocking moves away but we have only a fairly weak jet stream to drive low pressure systems our way. Just speculation, mind!

Fear not, the GEFS are a big swing in the cold direction at the end. In fact that's 2 successive upgrades from the GEFS now.

Edited March 9, 2016 by feb1991blizzard

[knocker]

5 minutes ago, feb1991blizzard said:

Fear not, the GEFS are a big swing in the cold direction at the end.

I'm intrigued feb - feel free to elucidate.

Edited March 9, 2016 by knocker

[feb1991blizzard]

5 minutes ago, knocker said:

I'm intrigued feb - feel free to elucidate.

http://www.meteociel.fr/cartes_obs/gens_display.php?ext=1&x=227.63999938964844&y=34.86000061035156

 

[knocker]

1 minute ago, feb1991blizzard said:

http://www.meteociel.fr/cartes_obs/gens_display.php?ext=1&x=227.63999938964844&y=34.86000061035156

 

Ah I see - that's a big swing. Right.