Model Output Discussion - Christmas and New Year

[Captain Shortwave]

The lack of wedge on both the UKMO and ECM means that low pressure rolls over the top, as such we see cold air coming from northern Greenland that feeds into the trough over Western Europe. Winds generally between the west and north, and still cold at the surface.

 

Edited December 24, 2020 by Captain Shortwave

[Mapantz]

A few frames from the UKV precip-type for Monday:

 

 

 

Edited December 24, 2020 by Mapantz

[Ice Day]

Comparing ECM at GFS at 192, I think we can safely say that FI is somewhat earlier in the run! 

 

Anything after 144 is best taken with a large dose of salt, which is ironic as I think we'll be needing a lot of that over the next couple of months!

[Tim Bland]

3 minutes ago, Mapantz said:

A few frames from the UKV precip-type for Monday:

 

 

 

Thanks Mapantz ...keep em coming please ECM very similar - the trend east continues over the last 24hrs although a bit more subtle now..

[Mike Poole]

11 minutes ago, Griff said:

Seems less keen to go west than GFS, I think... Not sure why but looks more consistent. 

Think the cut off low out west helps here, making sure our weather is not coming from the SW, by the ridging ahead of it.  T216:

Edited December 24, 2020 by Mike Poole
Got right chart finally!

[Tim Bland]

Incoming from the north west!!

[TSNWK]

ECM 216 initial reaction was WTF we have blown it with a low like that.. then I viewed the 850s whole uk apart from north western extreme at least -5 I have no idea what that chart would bring if it verified.

ps upstream and to our north look great.

[Battleground Snow]

Amazing ecm at 240,

Have a good Xmas all. Thanks for all the great contributions, will be back on boxing Day.

Time for die hard and some beer, will have a quick glance at the 18z runs of course 

 

[Griff]

3 minutes ago, Mike Poole said:

Think the cut off low out SW helps here, making sure our weather is not coming from the SW, by the ridging ahead of it.  T216:

I may have spoken too soon looks to be heading west at 240...

[Tim Bland]

Widespread heavy snow for most spreading south. With the usual eastward shift this would be another bingo! 

[Drifter]

16 minutes ago, Battleground Snow said:

Amazing ecm at 240,

Have a good Xmas all. Thanks for all the great contributions, will be back on boxing Day.

Time for die hard and some beer, will have a quick glance at the 18z runs of course 

 

That’s a couple of days away from mild south westerlies. Sorry to be Scrooge. 
 

Luckily it won’t pan out that way. 

Edited December 24, 2020 by Drifter

[I remember Atlantic 252]

2 minutes ago, Tim Bland said:

Widespread heavy snow for most spreading south. With the usual eastward shift this would be another bingo! 

big mild sector for south surely?

[That ECM]

1 minute ago, Tim Bland said:

Widespread heavy snow for most spreading south. With the usual eastward shift this would be another bingo! 

Just the 21 inches in Scotland.

[Tim Bland]

1 minute ago, Drifter said:

That’s a couple of days away from mild south westerlies. Sorry but be Scrooge. 
 

Luckily it won’t pan out that way. 

Eh? Have you seen the northern hemisphere view and that Greenland high? That low is cut off and sinking south?! 

[Kasim Awan]

Just now, radiohead said:

Thanks. What I was looking at uses a different algorithmn that produced 1-3cm. Nevermind.

The shortwave development 28th/29th is now almost a guarantee. 

The set up is more marginal I think than some are making out..

Good wind direction & precip intensity are key. At the mo we have a trend for the low centre to slide across southern UK from 28th PM which puts the interest for that precip area Sheffield & south. Disregarding Scotland atm. The surface marginality for the shortwave is below 250-300m (which is a rough base dewpoint 0C line with uppers of -4C & surface pressure of 960mb). This slice could be fairly easily eroded under a lengthy spell of precip and given the low speed etc could produce >10cm locally.

The shortwave intensity is far from resolved. A weaker shortwave as shown on the Arpege would limit precip significantly. Reasonable shortwave intensity is favoured now tho - so encouraging signs. 

By Boxing day when the models will have a better grasp of the low intensity (which influences the location of the shortwave precip and the likelihood of a snow event for many), a more firm assessment can be made. At the moment I shall stand firm on the above uncertainties mentioned.

[Methuselah]

3 minutes ago, TSNWK said:

ECM 216 initial reaction was WTF we have blown it with a low like that.. then I viewed the 850s whole uk apart from north western extreme at least -5 I have no idea what that chart would bring if it verified.

ps upstream and to our north look great.

Well, I wouldn't worry too much about the uppers: -4 to -6C is fine, when both SLP and heights are low. I suspect a lot of nowcasting might be the best way forward? 

[Biggin]

18 minutes ago, Tim Bland said:

Thanks Mapantz ...keep em coming please ECM very similar - the trend east continues over the last 24hrs although a bit more subtle now..

I will take that a few days away. Imby I would accept the low further south an add a Thames Streamer to it One can but dream.....

Edited December 24, 2020 by Biggin

[swfc]

6 minutes ago, Tim Bland said:

Eh? Have you seen the northern hemisphere view and that Greenland high? That low is cut off and sinking south?! 

Yes. But it's 10days away

[Geordiesnow]

An okay ECM, kinda similar to the UKMO at 144 hours which may suggest what might happen later on in the UKMO. Certainly no high pressure toppling in but its still a right old struggle to get significant cold air in.

So as it stands, the UK will remain on the cold side of the jet for a good while, snowfall will be hit and miss and be down to looking at the radar on the day itself, some sharp frosts also. 

[Drifter]

6 minutes ago, Tim Bland said:

Eh? Have you seen the northern hemisphere view and that Greenland high? That low is cut off and sinking south?! 

It looked to me as though the two Atlantic lows were in danger of phasing (copyright N. Sussex). 

[Allseasons-Si]

The jma at 192...

i would of loved to see where that day ten ECM went at day eleven,great NH chart that is.

[Man With Beard]

28 minutes ago, Tim Bland said:

Thanks Mapantz ...keep em coming please ECM very similar - the trend east continues over the last 24hrs although a bit more subtle now..

I'm feeling like did June 2019, when uppers were forecast 25C yet maxima around 30C ... I was screaming "The models must be wrong!!!" Yet of course they were right. What I'm feeling this time round is "Surely there has to be more precipitation than that on a low this big and this deep"!!! I mean come on, normally when you see a low like this you think "Flooding!" So for this, one of this biggest and most unstable lows ever, why is there not more rain/snow around this time? Yet no doubt the models will be right and I will be wrong - I guess it's because the fronts have cleared out of the centre (but surely there'd still be developments within the centre?) 

Edited December 24, 2020 by Man With Beard

[Methuselah]

4 minutes ago, Donegal said:

Snow or Snoexit. It will go down to the wire to find out..

If only David Davis were relating the models... Beast From The East? Easy -- less than a minute!

[sheikhy]

Cant complain bout the ecm!!brilliant all the way till 240 hours and on and off snow chances almost anywhere!!!

[Skullzrulerz]

Just now, sheikhy said:

Cant complain bout the ecm!!brilliant all the way till 240 hours and on and off snow chances almost anywhere!!!

Personally I prefer the GFS it seems to be a bit more stable in terms of cold air and as well as Greenland blocking 

ECM to me looks poised to fail