Model output discussion - The run up to Christmas

[sheikhy]

Just now, tight isobar said:

Rapid transition alerts @rain to snow.. via 6z!!!

Oiiiiii stop getting me excited!!!gfs out to 78 hours and no change so far over in the usa!!

[weirpig]

Upgrade on uppers at 84h  on the 6z   -8  across most if not all of the Uk  bar the far south

Edited December 21, 2020 by weirpig

[tight isobar]

2 minutes ago, sheikhy said:

Oiiiiii stop getting me excited!!!gfs out to 78 hours and no change so far over in the usa!!

The anti is upping... for sure 24/25.. on we go..

[Guest]

It really is pretty unusual to see such unanimous agreement from the GFS ensembles right though the entire run. Not a single cold outlier a only one mild outlier until the 3rd Jan. Coolest spell certainly seems likely down here since Feb-19, possibly March 18.

Surely nothing can go wrong from here? 

 

[sheikhy]

Even as early as 72 hours 850s are colder across england!!

[Captain Shortwave]

Hmm... interesting little feature moving south into the Low Countries on Thursday night.

the precipitation stays off shore, but with this running south with 850s of -6 to -8c. Still the chance for eastern areas, especially the south east and East Anglia.

Worth pointing out that this does not appear on the ECM or UKMO operationals as a surface wave (There might still be a trough feature present).

 

Edited December 21, 2020 by Captain Shortwave

[Anthony Burden]

43 minutes ago, Nick F said:

I would consider it a rather low possibility at the moment, none of this morning's models suggest snow across the south on the northern edge of the rain shield as it pulls away. Perhaps maybe over the Welsh mountains. Cold/dry enough air from the north not  catching up this rain unfortunately to allow it fall as snow.

A few wintry showers down eastern coastal areas on Xmas Day though, that 12/1 bet for Norwich White Xmas from William Hill perhaps would've been a good punt.

Hi Nick thanks for reply,latest gfs suggest could be marginal with 850 hpa very interesting times weather wise ahead.

[Methuselah]

24th's looking better...projected T850s of -8 or -9C look very favourable, for eastern/northern coastal parts, especially:

    

[weirpig]

Although  not full on snow  the icon does show the potential for a rain to snow event  in the next few days.  mainly for Wlaes  and the w Mids.   maybe worth keeping a eye on.

[tight isobar]

3 minutes ago, weirpig said:

Although  not full on snow  the icon does show the potential for a rain to snow event  in the next few days.  mainly for Wlaes  and the w Mids.   maybe worth keeping a eye on.

True back edge scenarios..as colder air digs-mixes south Kent/sussex.. look a good bet.. for at least transition sync!!!xmas eve/day!., and eastern most @east anglia..

Edited December 21, 2020 by tight isobar

[sheikhy]

Gfs same as 00z!!!nuttin to say except let the freeze begin!!!

[Stu_London]

I think the 27-29th period will see lots snow falling from the sky, but away from elevation quite a lot of wet slush.

Still a bit marginal and ground and soil temps could have done with a couple of severe frosts into them.

[danm]

24 minutes ago, goosey007 said:

Easterlys always a more fragile setup leading up to it.....more confident with current set of synoptics and more so consistency especially from the GFS over the last 3 days or so.....winter is comming ❄

Yes true easterlies tend to bring us the deepest cold compared to artic northerlies, however they can be a more fragile set up.

[ALL ABOARD]

Kudos to the GFS btw. 

It picked this pattern up and has run with it with only slight variants over the last few days. Considering we see it run 4 times a day and usually a custom to large swings it's been pretty remarkable. 

 

[Catacol]

8 hours ago, Scott Ingham said:

That high pressure over the Ural region has been very persistent and has been our friend. Very important piece of the jigsaw. I remember when i wanted that to persist n others were saying it was wasting time on winter you and catacol were on the same lines knowing we needed it for a ssw

The other notable feature so far has been the absence of the Pacific High sitting too far north. Prior to this season I thought a North Pacific high was a North Pacific high....until I stumbled on a very detailed winter analysis by Benchmark over at easternmassweather where I found that the precise location of the North Pacific high is of real significance. Makes sense, I suppose, that over the pond they would have a lot more interest in this feature is the same way that we get very specific about the placement of Greenland Highs! The latitude of this feature would appear to be linked to the character and placement of the Niña...and as our Niña has begun to look less and less of a CP event we have seen composites suggesting a flatter and less prominent NP ridge come to fruition. With low pressure therefore able to work eastwards from the Aleutians I am sure that this has magnified the Ural High/Aleutian Low partnership that I mentioned frequently in November. We are cashing in now.

The interlinked nature of all these sorts of features is the reason forecasting is so tough, and sometimes I think we just get lucky in picking an element of the pattern that does indeed begin to drive it. Don’t underestimate the links between low Kara sea ice and the prevalence of the Russian High. Back in 2019 we got excited by the major SSW and hung our hopes on it....but in that season this feature didn’t become a pattern DRIVER. Features and drivers are subtly and significantly different.

Anyway this season we appear to have rolled a double 6. Features that we know are good for U.K. cold appear to be becoming drivers of the pattern, and the seasonal forecast that I suspect concluded that a SSW was less than 50% likely and so was thrown out may well now bust. We still need to roll the dice and look for a good end product of a split SSW - but for now it’s enough to be happy with trop amplification creating blocking in our locale while at the same time aiding in bringing down the vortex. We still have many a day of model watching to go, and analysis to consider, before whatever is coming lands.

[tight isobar]

1 minute ago, Catacol said:

The other notable feature so far has been the absence of the Pacific High sitting too far north. Prior to this season I thought a North Pacific high was a North Pacific high....until I stumbled on a very detailed winter analysis by Benchmark over at easternmassweather where I found that the precise location of the North Pacific high is of real significance. Makes sense, I suppose, that over the pond they would have a lot more interest in this feature is the same way that we get very specific about the placement of Greenland Highs! The latitude of this feature would appear to be linked to the character and placement of the Niña...and as our Niña has begun to look less and less of a CP event we have seen composites suggesting a flatter and less prominent NP ridge come to fruition. With low pressure therefore able to work eastwards from the Aleutians I am sure that this has magnified the Ural High/Aleutian Low partnership that I mentioned frequently in November. We are cashing in now.

The interlinked nature of all these sorts of features is the reason forecasting is so tough, and sometimes I think we just get lucky in picking an element of the pattern that does indeed begin to drive it. Don’t underestimate the links between low Kara sea ice and the prevalence of the Russian High. Back in 2019 we got excited by the major SSW and hung our hopes on it....but in that season this feature didn’t become a pattern DRIVER. Features and drivers are subtly and significantly different.

Anyway this season we appear to have rolled a double 6. Features that we know are good for U.K. cold appear to be becoming drivers of the pattern, and the seasonal forecast that I suspect concluded that a SSW was less than 50% likely and so was thrown out may well now bust. We still need to roll the dice and look for a good end product of a split SSW - but for now it’s enough to be happy with trop amplification creating blocking in our locale while at the same time aiding in bringing down the vortex. We still have many a day of model watching to go, and analysis to consider, before whatever is coming lands.

I mentioned that pac-ridge early in @november!! It was a true spanner in the works time-after time...it’s evaporations have been working wonders

[BarometerCat]

As per the thread title...the run up to Christmas still looking good to turn colder after yet more rain tomorrow etc.. Chance of frost on Christmas day itself and somewhere in the UK still up for a surprise bit of snow Christmas eve or the day itself (East Anglia??)..  Cannot complain right now and is a better place than previous years.   Might feel a little more seasonal 

 

[TSNWK]

Will does griceland heights nudging east from about 200 meet with the Russian heights.....

[swfc]

Gfs introduces a low to the north west at 200+mark.not sure if its going to flatten things out, hopefully not. All fi I guess

[Premiere Neige]

41 minutes ago, Alderc said:

It really is pretty unusual to see such unanimous agreement from the GFS ensembles right though the entire run. Not a single cold outlier a only one mild outlier until the 3rd Jan. Coolest spell certainly seems likely down here since Feb-19, possibly March 18.

Surely nothing can go wrong from here? 

 

Don't say things like that  you'll jinx it! I hope you haven't been telling friends and family?!

[feb1991blizzard]

Imagine that blob of -2024 850hpa temps coming towards us over +ve sea temps, that would generate some serious convective snowfall.

Edited December 21, 2020 by feb1991blizzard

[Johnp]

12 minutes ago, Stu_London said:

-1 is not a severe frost

It is if it's in Fahrenheit

[weirpig]

2 minutes ago, swfc said:

Gfs introduces a low to the north west at 200+mark.not sure if its going to flatten things out, hopefully not. All fi I guess

just for fun at that range  Fi as you say  but looking at the jet i would have thought going to South.  Maybe.

[TSNWK]

2 minutes ago, swfc said:

Gfs introduces a low to the north west at 200+mark.not sure if its going to flatten things out, hopefully not. All fi I guess

Disrupter or Greenland ridge enforcing.. all gravy in my view.

[Methuselah]

4 minutes ago, feb1991blizzard said:

Imagine that blob of -2024 850hpa temps coming towards us over +ve sea temps, that would generate some serious convective snowfall.

Might be more than a tad nippy that, feb?