Model output discussion - here comes the beast!

[tight isobar]

!!!!

Gfs 6z wants to aim deepest of the cold core at ourselves...

Widespread -20 850s taking aim...

 

[ICE COLD]

WOW pretty much the whole country under -15 850s . Bloody amazing ?

[ICE COLD]

-17 into the south ?

[Scandinavian High.]

Uk in a bitter easterly flow heavy snow showers maybe some thunder snow.

[Glacier Point]

Thursday looking absolutely brutal cold with that wind chill.

Attacks from the north and south lining up, northern one expected to win out which means we go into week 2 cold.

[memories of 63]

I've got to drive fromLeeds to Newcastle on Monday,returning Wednesday.  Should I take a shovel?

[terrier]

Well the gfs06z raises the stakes even more. Frigid easterly with heavy snow moving across the country. Didn’t think these charts could get any better. But they seem to be upgrading nearer to the event. This really could be epic. 

[Yarmy]

 

Polar low approaching between Iceland and Scandi, while an Atlantic depression wants to track through Biscay to the south. Remarkable.

[TEITS]

Insane depth of cold.

One thing that stands out during the 1987 cold spell was the incredible icicles having off our school roof. With these low temps/dewpoints I imagine some impressive icicles will return next week!

[ICE COLD]

Getting buried in the south ?

[Scandinavian High.]

Could be wrong with this but low moving up from the south could bring blizzards to the southern England.

[tight isobar]

Central/southern england blizzard aligned..

On 6z gfs....

Burried!

[WalsallWeather123]

ARPEGE has corrected north over night aswell. 100% model agreement that UK will bear brunt of cold. No chance of the cold going south to France anymore. Time to get the shovels ready

[Nick F]

06z GFS op perhaps the start of correcting south in line with the other models wrt Friday's low moving into France - which previously had moving further north into UK, still some snow for southern counties, but would mean we keep the  bitter cold flow across all the UK and minus the less cold incursion with snow to sleet/rain in the south/southeast.

Edited February 23, 2018 by Nick F

[frosty ground]

8 minutes ago, memories of 63 said:

I've got to drive fromLeeds to Newcastle on Monday,returning Wednesday.  Should I take a shovel?

At a minimum. 

[ICE COLD]

The cold and snow still with us next Saturday . Another epic run . I have never seen model runs like this , never ever ?

[stodge]

Morning all

After a day of stellar output, "Wobbly Wednesday" seems a distant memory. Agreement on cold for certain but snowfall, well, that's a different kettle of frozen Birds Eye boil-in-the-bag haddock if you like with a lot of detail on instabilities and troughs to be resolved.

The initial snow potential from the east in the form of convective showers has also been joined by the possibility of snow moving up from the south later next week as the Atlantic makes an initial attempt to break down the cold block. For those arguing how hard it is to shift cold blocks, the truth is the January 1987 cold blast faded tamely by the end of that week so nothing is certain.

Anyway, I'm more interested in the future than the past and my remit takes me to Monday March 5th this morning.

Starting as always with ECM 00Z OP at T+240:

With HP over SE Greenland, a very long and complex trough dominates from the mid Atlantic through the British Isles to Scandinavia. The British Isles is on the cold side of that trough and is under a slack ENE'ly flow covered (apart from a Cornish wood shed) by -8 uppers. A new LP is moving NE and you'd fancy it would cross the British Isles from SW to NE so northern and north western areas look likely to remain cold with milder air coming up for other places so a transitional event with snow turning to rain and a fairly rapid thaw.

GEM 00Z a the same time:

Another complex evolution but not dissimilar to ECM with HP over Greenland and a broad complex trough covering most of North West Europe and Scandinavia. A deepening LP is entering the Bay of Biscay with a SSE'ly flow moving up over the British Isles introducing much milder air which has already reached the woodshed and looks to be extending north. The exact track of the LP is unclear and IF it stays to the south of the British Isles colder air will return from the NE but this is very uncertain at this time.

GFS 00Z OP at the same time:

A recognisably similar evolution to the other models. LP is in charge with one centre over Eastern Europe and another moving up from the SW but with the trajectory uncertain at this time. The coldest air has moved out of southern and western parts but -8 uppers remain to the north and east. Further into FI and it remains very unsettled - the LP to the SW comes up and crosses the British Isles deepening as it does so rain and snow for many but more LP are waiting and the next feature crosses the couth introducing warmer air but the north remains very cold and likely to see further snow.

GFS 00Z Control at T+240:

Colder than the OP but not dissimilar to the ECM with a slack trough over the British Isles extending SW into the Atlantic and NE into Scandinavia. Uppers remain at -8 or lower so snow showers to all levels. Further into FI and it remains very unsettled with rain for the south but snow likely further north.

The GEFS for 00Z at T+240:

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

I'm struck by the agreement - much less spread than has been the case over previous days. The main difference is of course over the trajectory of the LP systems. A majority of the members at this time keep the British Isles on the cold side of the trough, some put us in the battle ground but only two or three have brought the milder weather in by this stage. Moving further and there's a strong signal in the GEFS (albeit not reflected in the OP or Control) for pressure rises to the north or north east as we approach the middle of the month.

In summary, there's broad agreement across the medium range that we face a 7-10 day cold spell with some particularly cold air in the middle and end of next week. BY that time, the cold pool has become established over the British Isles but that has itself generated instability and a broad trough from mid Atlantic to Scandinavia. The British Isles sits on the cold side of the trough but with milder Atlantic systems moving up from the SW, the incursion of milder air to the south and west looks likely. The north and east look set to remain cold and it's entirely possible the LP systems will fail to shift the cold pool and simply top up the snow fields in the south in a battleground scenario. At this time it's too early to have any confidence but there are clear signals in the GEFS for new height rises to the north and east further into the month.

 

[Scandinavian High.]

The low coming in  southern England dumps lots of snow then pulls back south..

Edited February 23, 2018 by abbie123

[ICE COLD]

Max and min temps for next Saturday mid day . Still freezing ?

[Interitus]

41 minutes ago, Nick F said:

The EPS mean of -14C T850s into the SE UK is impressive enough, but this does leave the door open to those even colder ens verifying.

Lets hope we aren't heading for another Jan 1987 though, don't think the UK nowadays could cope.

 

This article from the Meteorological Society Weather journal is worth reading at this point - An historical and climatological note on snowfalls associated with cold pools in southern Britain - http://onlinelibrary.wiley.com/doi/10.1002/wea.666/pdf

Jan 1987 rates as the record deep cold pool at around 495/496 dam 1000-500mb thickness.

The authors say -

Quote

We now suggest that an occurrence of a
1000–500mbar thickness cold pool as low
as 516dam be considered deep over the
southern UK, posing a considerable threat
of locally disruptive snowfalls. We also
 propose that with 1000–500mbar thickness
levels below 500dam arriving from the east
only twice in the past 63 years, an intermediate
level of 508dam may be defined as a
very deep cold pool

In fact that whole edition of the journal from Jan 2011 is freely available and is a special issue focused on severe winter weather and worth a look for those inclined -

http://onlinelibrary.wiley.com/doi/10.1002/wea.v66.1/issuetoc

Edited February 23, 2018 by Interitus

[frosty ground]

Please note this is not a guarantee 

 

By Thursday expected snowfall totals..... (look away greater Manchester) 

 

[Interitus]

Double post

Edited February 23, 2018 by Interitus
Forum breaking again!

[Man With Beard]

21 minutes ago, ICE COLD said:

-17 into the south ?

Now this looks like a lot of the ECM ensembles this morning

[Nick F]

4 minutes ago, Interitus said:

This article from the Meteorological Society Weather journal is worth reading at this point - An historical and climatological note on snowfalls associated with cold pools in southern Britain - http://onlinelibrary.wiley.com/doi/10.1002/wea.666/pdf

Jan 1987 rates as the record deep cold pool at around 495/496 dam 1000-500mb thickness.

In fact that whole edition of the journal from Jan 2011 is freely available and is a special issue focused on severe winter weather and worth a look for those inclined -

http://onlinelibrary.wiley.com/doi/10.1002/wea.v66.1/issuetoc

Thanks for the links, will thoroughly enjoy reading those articles.

06z GFS goes for another attempt from the Atlantic to introduce milder air from the SW on Sunday 4th March, but wouldn't be surprised if this fails too like the Friday low coming into France and probably staying south of the UK. Have to pinch myself that these unusual synoptics showing are actually likely 

[beng]

5 minutes ago, frosty ground said:

Please note this is not a guarantee 

 

By Thursday expected snowfall totals..... (look away greater Manchester) 

 

That's probably a reasonable approximation of where the deepest snow will end up by the end of the week, just think we might in reality need to multiply the amounts by 3 based on the convection that will ultimately occur with the forecast temps.