The hunt for cold - Model discussion (late November)

[Rayth]

Thanks @mountain shadow And @Mike Poole

and if the mods would like to put this in the correct thread as I failed to do , thanks too  

[bluearmy]

The forecast for zonal flow high up in deep fi is fraught with operational inconsistencies- especially CFSv2 predictions 

however - better to see it predicted to fall than to rise ....... (it is currently going through a drop which will be followed by a recovery towards normal values .... and then .....)

[feb1991blizzard]

18 minutes ago, bluearmy said:

The forecast for zonal flow high up in deep fi is fraught with operational inconsistencies- especially CFSv2 predictions 

however - better to see it predicted to fall than to rise ....... (it is currently going through a drop which will be followed by a recovery towards normal values .... and then .....)

Some very stretched vortex charts right the way to the top appearing recently.

 

https://www.instantweathermaps.com/GFS-php/strat.php?run=2018112906&var=HGT&lev=1mb&hour=384

https://www.instantweathermaps.com/GFS-php/strat.php?run=2018112906&var=HGT&lev=10mb&hour=384

https://www.instantweathermaps.com/GFS-php/strat.php?run=2018112906&var=HGT&lev=30mb&hour=384

[Wilxy]

What a great run that was there is a lot of interest going into December and it’s far From a boring outlook!

[northwestsnow]

2 minutes ago, feb1991blizzard said:

Some very stretched vortex charts right the way to the top appearing recently.

 

https://www.instantweathermaps.com/GFS-php/strat.php?run=2018112906&var=HGT&lev=1mb&hour=384

https://www.instantweathermaps.com/GFS-php/strat.php?run=2018112906&var=HGT&lev=10mb&hour=384

https://www.instantweathermaps.com/GFS-php/strat.php?run=2018112906&var=HGT&lev=30mb&hour=384

Yes one thing we have seen little evidence of so far is an appetite for a strong Greenland PV.

[nick sussex]

Signs of a change as the high to the south edges west allowing pressure to drop to the east and se.

A note of caution though , we need to see this in the more reliable timeframe .

 

[feb1991blizzard]

2 minutes ago, northwestsnow said:

Yes one thing we have seen little evidence of so far is an appetite for a strong Greenland PV.

According to Lorenzo's post we MAY be struggling for an SSW until late Jan, TBH i would go further IF we dont get one in December, we could be struggling iuntil late feb or March once that +QBO has fully impacted the atmosphere, Though i suppose because its a transitional QBO winter we could have done just enough damage in Dec to weaken it enough for SSW to occur in Jan, others will have more informed opinions than me about this.

[Yarmy]

51 minutes ago, Mike Poole said:

Daily, based on the 0z GFS, I believe.  Below 0 would be a SSW if it was at 60N, not 65N - you can change the plot, simply change 65 to 60 in the URL.

Runs at 00:00UTC every day, so presumably it's based on either the GFS 18z or more likely the 12z. Hannah Attard's site is here:

http://www.atmos.albany.edu/student/hattard/realtime.php

I don't trust the GFS as it has a negative bias at range. NASA produces its own strat zonal wind analysis and forecast. The trend downward there is less pronounced (although it doesn't go out as far).

https://ozonewatch.gsfc.nasa.gov/meteorology/figures/merra2/wind/u60n_10_2018_merra2.pdf

Last year's analysis (the blue line) should also serve as a cautionary tale.

[bluearmy]

Anyone hoping for much guidance from the eps  clusters ...... forget it

6 of them out to day 10 and then three beyond

whilst the extended show a strong Atlantic upper trough across all three, they also show two clusters keen on ScEuro or Scandinavian height rises .... we can’t see how deep any central euro trough/low heights are in these scenarios so uncertain in any case 

Plenty (well pretty much everything post day 7) still to be resolved but given the background signals thus far, a renewed Scandinavian ridge wouldn’t be any surprise apart from those who feel we are in an unending phase of zonality ..... 

[Eskimo]

Could be a few surprises next week as a weak low pushes across southern UK

Edited November 29, 2018 by PerfectStorm

[SMU]

18 minutes ago, bluearmy said:

Anyone hoping for much guidance from the eps  clusters ...... forget it

6 of them out to day 10 and then three beyond

whilst the extended show a strong Atlantic upper trough across all three, they also show two clusters keen on ScEuro or Scandinavian height rises .... we can’t see how deep any central euro trough/low heights are in these scenarios so uncertain in any case 

Plenty (well pretty much everything post day 7) still to be resolved but given the background signals thus far, a renewed Scandinavian ridge wouldn’t be any surprise apart from those who feel we are in an unending phase of zonality ..... 

I think the general consensus is some sort of wedge steering the atlantic south at day 7-9 then a further pulse of WAA day 9-11 potentially reinforcing the block-

Could be a lot of transitory snow events in this period & possible more sustained cold especially in the North - ( Although based on history shallow systems sliding EW do often get moved further south as we approach T0 ) - GEM 00z looks a fair representation of the general evolution...

X

Edited November 29, 2018 by Steve Murr

[Man With Beard]

A fair assessment from the last two posts based upon the ECM ensembles - the Greenland mini-ridge is still consistently showing in clusters at around 8th December:

  

if anything, getting stronger with each modelled run (dangerous game forecasting Greenland height rises though!). Could lead to Atlantic troughs running south with back-end N/NWlies, enough to interest N and W areas in the snowy department.

What comes after, as @bluearmy points out, is a quandry, but not without potential for colder air to win out - these positive height anomalies to the north look like they could disrupt things for a few days after - by 14th December, we're either seeing the Atlantic lows driven further south than one would expect (again, northern hill-snow making territory), or we could see assistance being given to heights to our NE, with clusters 2 and 3 suggesting a potential west/east battle, which always allows for the chance of an eastern heights "win" and weather coming back towards us from the continent.

Betting wise, the D11-D15 period is probably 75% likely to be wet and cold and only 25% snowy and cold. So not particularly mouthwatering atm, but not a period to completely ignore.

[stodge]

Afternoon all

Having stepped away from the models for a couple of days, a shade disappointing to see the earlier promise of a blocked situation in early December not quite happening.

As I suspected, we are looking at a 7-10 day period minimum of Atlantic-influenced weather and that now looks to be 14 days as it's around T+288 on the GFS 06Z suite we see the next attempt at amplification. In truth, it's not wholly successful as the jet remains too powerful and the block in most instances gets blasted away but there are members where that doesn't happen and the Bearded One's call from the ECM ensembles looks about right at this time.

I thought the signal for blocking a little stronger earlier in the week - I do wonder if the pressure on the PV from the Eurasian side is causing the classic response of a re-location to the Canadian/Greenland side so you can add a further 7-10 days while that happens. 

 

[ArHu3]

4 hours ago, Raythan said:

Anyone know how often these update or is this a one off Plummet ? I’m presuming below 0 is SSW territory 

 

 

Last years we often saw these overshoot, in 1-2 days it will go up again

[Tim Bland]

3 hours ago, Steve Murr said:

I think the general consensus is some sort of wedge steering the atlantic south at day 7-9 then a further pulse of WAA day 9-11 potentially reinforcing the block-

Could be a lot of transitory snow events in this period & possible more sustained cold especially in the North - ( Although based on history shallow systems sliding EW do often get moved further south as we approach T0 ) - GEM 00z looks a fair representation of the general evolution...

X

Can’t see any snow south of Scotland on the GEM? 

[shaky]

Just come back from my delivery rounds and thought id check up on this forum!!blimey its dead!thought there would be a few comments on the icon 12 or sumin or even latest gfs!!

[Ali1977]

2 minutes ago, shaky said:

Just come back from my delivery rounds and thought id check up on this forum!!blimey its dead!thought there would be a few comments on the icon 12 or sumin or even latest gfs!!

Late winter now, model fatigue setting in I guess!! 

[Ross Andrew Hemphill]

Went from a snow event in Scotland to a snow event in Wales and the Midlands in about two runs, crazy...

[Weathizard]

Amazing how consistent the GFS is when it’s spewing out dirge, Sod’s law!!

[SMU]

Woeful 12z runs thus far - not even worthy of any commentary-

[BlueHedgehog074]

Maybe a possible rain, sleet and snow event next Tuesday for Central areas of the U.K on the 12Z GFS, as that shallow Low from the South-West bumps up against the colder air further North.

(No doubt, it could look a bit different again on the next run, but just an observation).

Edited November 29, 2018 by DiagonalRedLine

[mb018538]

Sod it, let’s all go to Spain for a few days. 850s up at 10-15c and temps forecast into the low 20s Into next week!

[swfc]

31 minutes ago, Weathizard said:

Amazing how consistent the GFS is when it’s spewing out dirge, Sod’s law!!

Maybe it's s data issue due to the run up to Xmas!!! Sorry I always wanted to say that.Anyway the changes from run to run maybe  a sign that the atmosphere is in a state of flux given the back ground signals??I'm not quite sure where that leaves the next few runs ete.Tbh I'm not sure what I'm talking about so on the strength of that alone IL "get my coat"and await the EC 12z 

Edited November 29, 2018 by swfc

[mb018538]

Basically it means that we’ve dodged the zonal bullet for months and are getting our comeuppance now. First half of December is looking like it’s going straight into the bin sadly. Let’s hope the minor warming shakes things up a bit.

[Mucka]

I think what we are seeing is the models move toward a cool/cold zonal flow with temporary Atlantic ridges allow for brief drier interludes and colder from the North - so a move away from a definitive pattern change with Northern blocking.

This will make for fairly typical Dec conditions with a chance of transient wintriness mainly in the North but if we clutch a straw the right set up could at least give snow to low levels though it wouldn't stick around.

This pattern couldn't sustain and eventually it would turn more typical zonal again and we would then await the next chance.

This would be disappointing and a let down for those who have forecast a true pattern change to blocking - which included me I might add.

There is still the chance the models are overdoing the Atlantic thrust and the potential for an Atlantic ridge to be more resilient which could at least give a proper cold snap and maybe lead to a true pattern change so all not lost yet.

And finally there is always the small chance of something else popping up.

The search for cold goes on.