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Paul

Model output discussion - Post SSW - Will it turn cold?

Paul

Please only post model discussion in this thread. 

For more general chat and banter, or moans and ramps loosely around the models, please head to the banter thread:
https://www.netweather.tv/forum/topic/86721-model-moans-ramps-and-banter/

For general weather chat including about the snow/cold chances around the country, please go to the regional threads:
https://www.netweather.tv/forum/forum/142-regional-discussions/

Thank you!

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6 minutes ago, Tamara said:

I quite often agree with your sort of sentiment, as I'm one who opts to look at the most likely solution to fit the signals rather than the preferred one:)

But, equally impartially and with intended objectivity (hopefully):

The situation at present is a highly unusual one and the risk of some astonishing late season wintry weather is much higher than usual, certainly than often seen in these cases where deep cold pool advection flirting with the UK graces the perimeters of more 'reliable' NWP

The repercussions of this SSW are going to be sustained. The clock starting ticking back in January and carried on through this month with extreme instability of the atmospheric profile with the tropics and extra tropics being subjected to opposing high amplitude states of angular momentum tendency.

gltend.sig.90day.gif

The impact on tropospheric global wind-flows (the Jetstream) has been significant, in addition to the detonation of some intense cold pooling over the polar field (relative to the modern day generally warmer arctic) : more especially across the Canadian arctic as multiple programmes of hot needles are probed into the polar stratosphere

The result of extreme tropical momentum and stratospheric implosion implies high impact weather events on a broad-scale. Some places are going to get bitterly cold and some weirdly warm. 

In this day and age fewer parts of a hemisphere can get cold with less to go around than used to be the case maybe. But this programme of events strongly favours the European sector to become bitterly cold from what looks to be an impressively large breakaway cold pool for the time of year from Siberia. While its true that the envelope of this cold has boundaries that shift in intra suite modelling, the focus of the BI being impacted in inclusion, is much higher than other situations where lesser broad-scale drivers have been in evidence

Ramping indeed requires a justification - I think this situation fits that criteria. Areas of land mass infrastructure most at risk aside from weather impacts, the synoptic blocking pattern and its associated reverse polarity from one side of the Northern Hemisphere to the other - is not something seen on an every day NWP menu:)

And certainly now the signs are stronger, but how many times have we been in this situation only for a cold spell to get watered down or just flat out blow away?

i want a few feet of snow, but I’ve been lurking on here long enough to know that it doesn’t always happen the way models say it will. Sometimes one model can be the only one that sees the truth, sometimes it can be just wrong, we’ll find out.

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it is interesting to read all of the comments on ECM and how if it shows something different it must be followed. I have to admit I am totally confused by this. Correct me if I am wrong but the ecm has flipped more than any other model going into this scenario starting at the weekend in Ernest. if there was a chance of this being delayed or reduced time scale, I very much doubt the super computers at Exeter would have released this statement, otherwise they would be left with egg on their faces, like the bbq summer as an example despite that being a long range forecast.....

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15 minutes ago, Man With Beard said:

So, assuming for a moment that the GFS 06Z verifies, how would it compare with past cold spells?

GFS 06Z T156

gfs-1-156.png?6

March 2013: GFS 06Z is ever so slightly slightly colder

archives-2013-3-11-12-1.png

Feb 2009: colder again

archives-2009-2-2-0-1.png

Feb 1991: just falls short but a close thing

archives-1991-2-7-0-1.png

Jan 1987: no, not close

archives-1987-1-12-12-1.png

 

 

but the 06z wouldn't be quite as cold, even if the pattern verified - the charts from a week away are always moderated a bit 

 

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1 minute ago, Jimmyh said:

it is interesting to read all of the comments on ECM and how if it shows something different it must be followed. I have to admit I am totally confused by this. Correct me if I am wrong but the ecm has flipped more than any other model going into this scenario starting at the weekend in Ernest. if there was a chance of this being delayed or reduced time scale, I very much doubt the super computers at Exeter would have released this statement, otherwise they would be left with egg on their faces, like the bbq summer as an example despite that being a long range forecast.....

I'm correcting you ............

none of the models have covered themselves in glory - hence the gem currently verifying slightly ahead of ecm

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3 minutes ago, bluearmy said:

but the 06z wouldn't be quite as cold, even if the pattern verified - the charts from a week away are always moderated a bit 

 

Do they, it does make one question how extreme weather events have ever happened in this country.

Edited by frosty ground

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I just really need to see this get below T100 and have agreement. An adjustment for more widespread snow - low pressure fronts - crucial imby also.

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4 minutes ago, frosty ground said:

Do they, it does make one question how extreme weather events have ever happened in this country.

A fair point and there will always be the exception to prove the rule, but what BA states is correct and is a perfectly natural consequence of increasing error with respect to time - i.e how the models will progressively leave the norm in the further reaches of their output.  Think about how many GFS dart board lows we see toned down by T0, phantom easterlies (various models) that never materialise, etc.  However "not quite as cold" would still be perfectly sufficient for what most are chasing on here and the expected moderation of temps may go hand in hand with increased chance of precipitation. :) 

 

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It probably shouldn't come as a shock, but all the met office forecast stuff has been removed - please head to the relevant threads to discuss things other than the models. 

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Looking at the gem ens mean (geps) for next Tuesday (taken from last Monday) and thinking this is a model we should be paying more attention to !!

496CA007-0CFF-44D4-AF85-9387C4CDF7A9.thumb.jpeg.213f284a7c3ea1f816d5ea5be94fbfce.jpeg

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1 hour ago, Seasonality said:

Look at @carinthian's post immediately above yours, his sources are sceptical of the ECM output. So yes, agree that only a fool would outright ignore the output, but it seems that some experts are not convinced of it offering the correct solution.

I very much doubt that any of the models has got this 100% right at this range, including the ECM.A blending of the options would provide a very good event for many parts of the country. I wouldn't get too hung up on any one output, either positive or negative at this stage as long as the trends remain broadly the same. As others have alluded too, including some of the most technically gifted on here, this is a very different situation to the norm so I would not be expecting normal outcomes for the UK from this forthcoming episode of weather.

I have in my post on Saturday morning nailed my flag to the mast in terms of what I think will be a likely outcome. Not a lot has changed in terms of my thinking. I therefore rather boldy in a senior managers meeting this morning warned my colleagues of the potential weather event and the disruption that it could have to our business. I gave the likelihood of severe disruption at around 40% ( we are based in the Chilterns) and recommended that we keep a very close eye on the situation and make sure we are prepared in terms of our staffing and customer communications, implementation of bad weather policy, plenty of grit etc. I hope the met office get it out there to businesses as soon as it is practical to do so. Not every business has a weather geek in their senior management team ! 

 

 

 

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35 minutes ago, Jimmyh said:

it is interesting to read all of the comments on ECM and how if it shows something different it must be followed. I have to admit I am totally confused by this. Correct me if I am wrong but the ecm has flipped more than any other model going into this scenario starting at the weekend in Ernest. if there was a chance of this being delayed or reduced time scale, I very much doubt the super computers at Exeter would have released this statement, otherwise they would be left with egg on their faces, like the bbq summer as an example despite that being a long range forecast.....

Met largely go by MOGREPS we are none the wiser however @essexweather did post lately we used to have IF reveal snippets it’s superior guidance compared to ECM however it too is incorporated. We have a mean like this at day 6! If you’re from Southern England then it should make you ecstatic unless you’re knocks, severe cold looks odds on for south, snowy conditions more uncertain particularly the northern extent.

EF2292E1-1D93-4C6A-8E6C-993837521C54.thumb.png.d6ff7855fc00ee1d4a44144f2c887261.png

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Another tense set of runs coming up,  Arpege and ICON 06z's heading the right way (better ridging/Atlantic profile). 

Remember that regardless of whether or not the 12z's show what we all want (or don't) that this is unlikely to be set in stone this evening. S4lancia's post above is worth taking stock of- run to run variation happens every time. 

I have to say it's been some of the best model watching over the last few weeks,  watching the SSW being forecast and then coming to fruition with a devastating affect on the tropospheric vortex coming - pure synoptic heaven.  Hopefully this beast lands...  It's long overdue. 

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29 minutes ago, bluearmy said:

Looking at the gem ens mean (geps) for next Tuesday (taken from last Monday) and thinking this is a model we should be paying more attention to !!

496CA007-0CFF-44D4-AF85-9387C4CDF7A9.thumb.jpeg.213f284a7c3ea1f816d5ea5be94fbfce.jpeg

Yes and as I posted earlier here is the mean for next Wednesday

gens-0-1-228.png  Just saying:D

gens-0-1-216.png

gens-0-1-216.png

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We're definitely heading into twitchy toes time with the runs this afternoon, tonight and tomorrow. If we still have no clear pattern by tomorrow night I'd be concerned.

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I know we always say this but due to the high impact this cold spell could have and the fact we're less than a week out, this afternoon's ECM is huge- one of the most important I can think of. If it sings from the GFS hymn sheet, we can be fairly confident of the way this pattern will evolve and if we really will get snowmaggedon! I for one am nervous... 

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3 minutes ago, Deep Snow please said:

We're definitely heading into twitchy toes time with the runs this afternoon, tonight and tomorrow. If we still have no clear pattern by tomorrow night I'd be concerned.

Mmmmm.....possibly, however, most folks are posting charts that are still 7 to 10 days out ( and ramping them up IMO...not there's anything wrong with that...i love a decent cold chart !! )....i'd give it a few more days before you allow your toes to twitch !!

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1 minute ago, ZK099 said:

I know we always say this but due to the high impact this cold spell could have and the fact we're less than a week out, this afternoon's ECM is huge- one of the most important I can think of. If it sings from the GFS hymn sheet, we can be fairly confident of the way this pattern will evolve and if we really will get snowmaggedon! I for one am nervous... 

Firstly we need gfs to stick to its current output lol as that comes out first!!!if it continues with the wintry output on the 12z then i expect ecm to look better this evening!!if not then i expexct madness in this forum and paul is gona have a big job on his hands lol!!

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Afternoon all :)

Late to the discussion party today as I have a life beyond forecast charts, model output and the like.

Last evening, on a rare weekend foray into the thread, I opined we might face a stand-off or trade-off in terms of medium term evolution (I'll leave the agonising over T+72 - T+96 to others) between a short, intense, very cold snowy spell followed by a substantial thaw from the south and a more extended colder but drier period.

The positioning of the controlling Scandinavian HP is vital - too far north and the immediate chances of snow and cold increase but leave us more vulnerable to the Atlantic from the west and south and especially so if we move to a west-based negative NAO. Too far south and while the longevity of cold is likely especially via retrogression to Greenland, there's less chance of snow which is after all what most here want.

So it's a fine balancing act if you want both snow and an extended period of cold making sure we are on the cold side of the east-west trough.

Some extraordinary output over the weekend, any single example of which would have reduced the forum to meltdown in the past four years. As it is, if the uppers are less than -12 it's a downgrade. Incredible.

So where are we going into March with the charts of the first day of spring (allegedly) - starting with ECM 00Z at T+240:

ECM1-240.GIF?19-12

The HP has retrogressed but maintains a strong SE'ly ridge right down to the Bay of Biscay. A light NE'ly flow covers the British Isles with a small disturbance over Holland. 850s of -4 to -8 suggest some wintry precipitation to high ground but the far north west dry and fine. There is colder air to the NE again but the extent to which this can push SW remains to be seen.

GEM 00Z OP at the same time:

gem-0-240.png?00

An intense HP over SE Greenland controls the weather with a ridge ESE across the Faeroes to Scandinavia. LP is over Iberia and in between the British Isles is in a strong E or ENE'ly flow. 850s are -12 over southern England with -16 uppers over Northern France. Any precipitation would be of snow with drifting in the strong winds and a pronounced wind-chill. Much drier over northern Scotland and Ulster though with severe overnight frosts.

GFS 00Z OP at T+240:

gfs-0-240.png

A large anticyclone over Greenland ridges SE toward the British Isles. Between that and LP over the Adriatic and Scandinavia a NNE'ly flow covers the British Isles. 850s generally between -4 and -8 as the coldest air departs south. Some wintry showers to southern and eastern coasts but drier further north and west. The cold weather is on its way out as a ridge pushes up from the south and very soon "normal service" is resumed with a westerly flow and much milder air.

GFS 06Z OP at T+234:

gfs-0-234.png?6

LP is over the Channel and an ESE'ly flow covers the British isles. Cold air remains to the north and west but much milder air is in to the SE but, I suspect, with plenty of rain and showers with snow further north as a transitional frontal band moves north and north-west. Further into FI a broadly Easterly flow remains in place with signs of as renewed pressure rise over Scandinavia at the very end of FI.

GFS 06Z Control at T+240:

gens-0-1-240.png

Signs of a west-based negative NAO and a small LP has spun up from the SW and while currently over the SE of England is going to swing up the east coast with much milder air on its eastern flank while very cold air (850s of -8 to -12) remains to the west over the bulk of England and Wales. Further into FI and it turns milder for all briefly before the winds swing back NE'ly and a new plunge of very cold air looms.

Looking at the T+240 GEFS:

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

Some seem to want to bring milder Atlantic air from the SW via the west-based negative NAO, others go for an attack from the south but a lot of members are still very cold at this time. Going further into FI and I note a growing tendency for the GEFS to indicate a flow from the N or NE returning some very cold air across the British Isles.

In summary, another day of extraordinary chart output but little is resolved. GFS seems keen to promote a breakdown at the T+240 stage but they may just be playing the progressive card and indeed signs even within the GEFS suite any milder spell could be quite short-lived. No such issues with ECM and GEM which keep Britain firmly in the cold - both promote retrogression but fans of snow will prefer GEM which has more possibilities than ECM which keeps the stronger anticyclonic influence.

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Just now, K9 said:

Mmmmm.....possibly, however, most folks are posting charts that are still 7 to 10 days out ( and ramping them up IMO...not there's anything wrong with that...i love a decent cold chart !! )....i'd give it a few more days before you allow your toes to twitch !!

Well I think everyone is pretty confident on the synoptic pattern that is about to evolve. The only question is where the high will sit. If the ECM corrects northwards on the next two/three runs I think we can get excited

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21 minutes ago, winterof79 said:

Yes and as I posted earlier here is the mean for next Wednesday

gens-0-1-228.png  Just saying:D

gens-0-1-216.png

gens-0-1-216.png

They’re controls ??

from memory the mean is like ec mean 

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1 minute ago, ZK099 said:

Well I think everyone is pretty confident on the synoptic pattern that is about to evolve. The only question is where the high will sit. If the ECM corrects northwards on the next two/three runs I think we can get excited

Fair point...i just like to get to around +96 before i allow a smile to break out...seen far too many 'garden paths' since the olden days of the 'BBC Forum' where it all crashed and burned ( even at +48 TBH !! ) at the last minute....great model outputs though courtesy of the SSW...eyes down for a full house over the next few days !!

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1 minute ago, bluearmy said:

They’re controls ??

from memory the mean is like ec mean 

Forgive me you are correct GEM slightly better.

gens-21-1-204.png

EDM1-192.GIF?19-12

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