Model output discussion - The run up to Christmas

[iowpompeylee]

21 minutes ago, Mr Frost said:

Wee look ahead to the 28/12...

Latest UKV precipitation type snapshots below:

06:00

 

09:00

 

12:00

 

Still five days away - subject to much change at this range!

Great to see a bit of wintry weather showing for you ladies and gents down South! 

If we can get a fairly widespread snow event (even a dusting) within the next seven/ten days for the UK/Ireland...it would calm down the nerves in this thread a wee bit with regards to the rest of Winter! 

All the best! 

As a southerner I love this post! I do think there are plenty of twists and turns. I think anybody could get snow anywhere in the next couple of weeks!! 

Edited December 23, 2020 by iowpompeylee

[iowpompeylee]

Regarding Xmas eve and Xmas day, the temps must be cold enough to give a few wintery showers? Anything showing shorterm on outputs? 

Edited December 23, 2020 by iowpompeylee

[andymusic]

3 minutes ago, iowpompeylee said:

Regarding Xmas eve and Xmas day, the temps must be cold enough to give a few wintery showers? Anything showing on outputs? 

Euro 4 is giving this for xmas day London way - might be a bit optimistic though

[bluearmy]

49 minutes ago, chionomaniac said:

How ridiculous to post this. The stratospheric disturbance is still forecast. There is still a significant amount of wave 2 activity - and this is being trop driven. And, if the trop is the driver, then this is where we need to concentrate atm. The strat disruption will help later. So laugh away....

Ignore that particular poster Ed ....... Seems either to lack knowledge (not a crime) or is just a troll (which should be )  

Edit from Ed. It’s sorted lol

Edited December 23, 2020 by chionomaniac
To make ba aware

[Skullzrulerz]

6 minutes ago, iowpompeylee said:

Regarding Xmas eve and Xmas day, the temps must be cold enough to give a few wintery showers? Anything showing shorterm on outputs? 

They may be a few snow showers around the coasts of eastern England possibly East Anglia

[iowpompeylee]

3 minutes ago, andymusic said:

Euro 4 is giving this for xmas day London way - might be a bit optimistic though

That looks promising, the wind will be potent, going to feel very cold in the windchill! Could be a few surprises! 

[Cold Winter Night]

Hello,

First post by a long time lurker from the Netherlands here.

What stands out to me in the most recent output is not only what is happening upstream, but also the development of the high in Russia. The models are making more of it each run. Stronger and slightly further North.

For now it is blocking the very cold Siberian air from moving West, but if it gets far enough to the North(West) it might link with the Greenland high.
That would cut off the potential Northerly, but open a gate to the East.

Yesterday's ECM 12Z for New Year's Day, and today's 12Z.

 

[northwestsnow]

The EC det brings an Ice day in the Pennines day 9,after a night at -6 ....

If I'm reading it right   

[Skullzrulerz]

Could be a nice Christmas treat for a few folk looks a sight upgrade on AROME

[joggs]

1 hour ago, Kasim Awan said:

There's no point fixating on a particular T850 value as the hallmark for snow.

There are around 25 factors that influence the T850s required for snow.

For example, low heights, which move the altitude of 850hpa down by about 200 metres. This automatically drops the T850 requirement by 1-2C. For example, a -4C 850 temp in high heights would produce a 1500m temp of -4C, however in low heights T850 is near 1300m so a -4C T850 would produce a Temp at 1500m of -6C..

In the set up modelled for 27th-29th, surface inversions will form a cold layer up to 2000ft asl. This reduces the T850 requirements, as they do not need to be at the depth of cold needed to ensure the entire troposphere is freezing due to the presence of an inversion. So uppers of -2/-3C can suffice if this permits the temp to remain below 0 from the T850 level to the top of the inversion! Given we have both low heights & light winds 27th-29th, these two mechanisms will work to reduce the T850 requirements.

4th March 2016. Low lying Cheshire got 4". T850s of -2C, evap cooling sets up a superficial inversion (the temps don't decrease near the surface, but the top-down lapse rates drop to near 0 permitting -2C uppers to be just tidy indeed). Even 0C uppers can suffice if evap cooling drops the top-down lapse rate to 0 so that effectively the air does not warm as the snowflake falls near the surface). So theoretically uppers of 0C and a surface inversion could produce heavy icy snow / blizzard. But...

Marginality - precip too light and you will fail to get the evap cooling needed to reduce the top-down lapse rate, keeping the surface warm. Strong winds, shore wind, the Fohen effect, urban heat island, and about a gazillian other factors can do the same.

So hopefully this will clear up the T850 debate once and for all. It is a lot more complex than a single figure. Ultimately the potential is there for "high" T850s to produce amazing events.

It is up to meteorologists to determine the contribution of ALL these factors and how this will impact the precip state. 

Top post

[iowpompeylee]

Just now, Skullzrulerz said:

Could be a nice Christmas treat for a few folk looks a sight upgrade on AROME

I’m hoping it can drift further inland, I’m sure there will be a bit more precipitation about! On the big day

[Lampostwatcher]

1 minute ago, Skullzrulerz said:

Could be a nice Christmas treat for a few folk looks a sight upgrade on AROME

 

[Lampostwatcher]

Just now, Lampostwatcher said:

 

Slight dusting possible I'd imagine 

[Battleground Snow]

Really great mean at 240, obviously these highs have failed to materialise in recent years, but with the lack of energy over the states and the Russia high firmly in place you would hope it has a really good chance of verifying - hoping @Daniel* can show us the extended too.

 

 

 

[Mike Poole]

ECM mean and spread T240:

GEFS mean and spread T240:

A lot more uncertainty on ECM than GFS, normally that would urge caution, but given GFS performance on this one, I’m going the other way, the GFS has the mojo, it has done for days, and the ensembles back the op.  

[NewEra21]

6 minutes ago, Skullzrulerz said:

Could be a nice Christmas treat for a few folk looks a sight upgrade on AROME

Would be a very nice xmas eve to see a few flakes falling under the Christmas lights! I'll definitely be keeping my eyes peeled 

[SMU]

^^^ The ECM mean however is much better than the GFS mean at 240, infact its superb!

despite the uncertainty...

debilt T2Ms will be heading down towards 0C late on tonight...

Edited December 23, 2020 by Steve Murr

[northwestsnow]

ec mean shows an Omega block...

[Pembroke Dangler]

34 minutes ago, northwestsnow said:

At 162 hrs, according to weather.us,

IMBY I'm seeing 22 in farenheight for my location...

I'm not entirely sure that's right!

That would equate to -5.5 Celsius? 

 

I believe they factor wind chill into the forecast temperature over there where as out forecast just gives raw temperature. 

[Dazzer6666]

9 minutes ago, Skullzrulerz said:

Could be a nice Christmas treat for a few folk looks a sight upgrade on AROME

Can I bank that now ?

[Decemberof2010]

[kold weather]

GFS ensembles are very unsure exactly where and how strong any upper blocking develops, so plenty of options out there for what may happen. The one thing there is some decent agreement with is the general trend of southerly track tracking jet with LPs either over us or just to our south, and also for an upper high pressure somewhere to our north. Put the two together and you have a decent chance at a snow event or a sustained cold event, with a bit of luck both.

[bluearmy]

Extended eps are very reflective of the gfs 12z op with more than a hint of a west based neg nao and a cold plunge headed south forced by the greeny ridge .....the control run similar to the gfs op.  high risk = high reward (which wouldn’t compensate for someone looking at a wet garden whilst fifty miles range is white ). No imbyism here please! 

[northwestsnow]

1 minute ago, bluearmy said:

Extended eps are very reflective of the gfs 12z op with more than a hint of a west based neg nao and a cold plunge headed south forced by the greeny ridge .....the control run similar to the gfs op.  high risk = high reward (which wouldn’t compensate for someone looking at a wet garden whilst fifty miles range is white ). No imbyism here please! 

The plot thickens.....

[Howie]

1 minute ago, bluearmy said:

Extended eps are very reflective of the gfs 12z op with more than a hint of a west based neg nao and a cold plunge headed south forced by the greeny ridge .....the control run similar to the gfs op.  high risk = high reward (which wouldn’t compensate for someone looking at a wet garden whilst fifty miles range is white ). No imbyism here please! 

I was hoping the west based -NAO would do one, ugh