Model output discussion - The run up to Christmas

[mountain shadow]

An all mighty wet slush fest away from hills and mountains and we're still chasing proper cold in the + day 10 range.

Still time for change though.

[KTtom]

Some nice charts on display again this morning, especially around the turn of the year, it seems in this country you have a choice, very cold and dry, or less cold but a greater chance of heavy precipitation, we can't have both here in the UK. The period to the end of the year looks like the latter.

This chart from the ECM is probably the one which caught my eye more than any this monrning...when was the last time you've seen the vortex like this at a time when traditionally its at its most organised..If we get Strat intervention there won't be anything left by the end of Jan! 

 

[iowpompeylee]

1 hour ago, Battleground Snow said:

Very quiet this morning considering the output, GFS is very close to something special, won't take much adjustment east of that "true Greenland high"

I have been impressed with the consistency of the GFS, can't remember so many runs where it churns out similar output past 192.

Ukmo looks decent too, will be interested to see the ECM at 192, I suspect it will move to the GFS again.

Model watching fatigue has hit early this year

[Matt H]

I’ve definitely seen worse day 10 ensemble means!

[Frosty.]

Shirley there will be some snaw soon?..crimbo eve for some of us according too the GEFS 0z?...and then plenty of potential at times, right into early January!!!!!!

Edited December 22, 2020 by Jon Snow

[Daniel*]

31 minutes ago, Stu_London said:

It's only brilliant output if you like looking at projections at D9, D10, D11 onwards etc.

There is a shorter interlude of below average temps, which as ever at this time of year, has potential to deliver a few transient snow events in favoured places.

At present there is no evidence to suggest any sustained cold spell.

You must be viewing different output to me. The day 6 projection looks fun to me on ECM, marginal aloft yes but there could be some surprise snowfall just about anywhere with this set up. Slacker winds and snow cover and it could become very cold on surface. We could generate our own cold in fact.

 

[Joe Bloggs]

No complaints about the 00z output from me. 
 

A blocked Atlantic across the board. Yes the cold air isn’t QUITE there for the period immediately after Christmas  but that could well get upgraded and anywhere with altitude, especially in the north, may strike it lucky. 
 

Normally at this stage, into FI, we’d be seeing signs of the ridge flattening with the Atlantic taking over. It’s really reassuring to see continued bouts of blocking continuing to crop up - a signal that this could be a fairly extended spell of below average temps if we’re lucky. 
 

It would be really beneficial for us if we could somehow get the synoptics to align to deliver some proper Arctic air (-10C at 850 hPa) at some stage. This would allow more surface cooling and could make a difference when it comes to more marginal events down the line. 
 

As for NWS’s comments about easterlies - yes these benefit the Pennines, but for large areas of the NW, especially closer to the Irish Sea, a deep cold convective WNW’ly can actually be our biggest snow maker - think December 2009. 
 

Definitely the most interesting model watching for a considerable time. Reminds me a bit of the run up to December 2009 when it looked consistently promising for days on end - the air was just that bit colder back then to give more guaranteed snow opportunities for lower elevations.
 

All in all it’s looking very good.   

[IDO]

The gefs at d12 are not yet conclusive for how the pattern develops from the third ridge post-d7. Certainly the op is the most progressive by d10 with the Greenland wedge, but it is not until d12 it gets a solid cluster in the ens. There are however maybe two more options with similar support...

d12 gefs> London> 

...the Atlantic high (rebounding at times) and the NW>SE flow. This still needs to be resolved. Still a solid 850's mean running through to d16 in my area, so an extended seasonal flow, with maybe after d12, some signs of a few members moving colder. There are the usual humbug runs mixed in of course.

Looking an interesting 10 days from Thursday and the door remains open in FI for further possibilities.

 

 

[Stu_London]

4 minutes ago, Daniel* said:

You must be viewing different output to me. The day 6 projection looks fun to me on ECM, marginal aloft yes but there could be some surprise snowfall just about anywhere with this set up. Slacker winds and snow cover and it could become very cold on surface. We could generate our own cold in fact.

 

I don't disagree that a few surprises might pop up. I don't think air temps and possibly more importantly ground temps will support any long lasting snowfields that would support any lower of temperatures near the surface. More likely some might awake to a covering that is largely disappeared by the middle of the day.

As most in the forum appear to be seeking a cold spell with a perhaps more than a few hours of snow cover, away from 300m + elevation, I don't see this set delivering. I'd be happy to be proved wrong however.

 

 

[TSNWK]

21 minutes ago, Daniel* said:

You must be viewing different output to me. The day 6 projection looks fun to me on ECM, marginal aloft yes but there could be some surprise snowfall just about anywhere with this set up. Slacker winds and snow cover and it could become very cold on surface. We could generate our own cold in fact.

 

That bottom chart really cheered me up this morning.  As I was  sensing things were being pushed back.   Ice day in rural south east England is  nothing to be sniffed at. 

Hopefully some decent frosts at least to get into the ground.. 

[carinthian]

On 21/12/2020 at 06:03, carinthian said:

Morning all. Good agreement between UKMO and GFS at 144t. Maybe UKMO speeding up the advance of the cold front on Boxing Day. Chance of snowfall in parts of SE Britain now increases to 30% based on the formula I mentioned yesterday from 29th December. Looks like the low will become elongated just to the east of the British Isles as we head towards the New Year with its centre close to the Low countries. Not a bad place to produce a prolonged colder spell.

Should get an up-date in an hour or so from the portal team over here.

C

 

Morning all. I have an update from the team over here in relation to the above post sent yesterday morning. Based on the current consistency shown by the models this morning , the outer perimeter results shown by the snow model computer increases the risk of snow now to 40 %  during the period 29th /30th Dececember. They forecast  spreading out of the 1000-500mb thickness ( dam ) value of 528 or slightly below over England and Wales especially. These values would be in the range for snow to occur. The exact location cannot yet be determined  ( maybe with-in 48hours period if current synoptic persist ).  By New Year they expect the trough to align its axis from Greenland to Northern Germany , which is good news for extending the colder and possibly snowy conditions with-in the British Isles .

C

[Daniel*]

17 minutes ago, Stu_London said:

I don't disagree that a few surprises might pop up. I don't think air temps and possibly more importantly ground temps will support any long lasting snowfields that would support any lower of temperatures near the surface. More likely some might awake to a covering that is largely disappeared by the middle of the day.

As most in the forum appear to be seeking a cold spell with a perhaps more than a few hours of snow cover, away from 300m + elevation, I don't see this set delivering. I'd be happy to be proved wrong however.

 

 

I think this set up has strong potential to be colder than it looks given uppers. I’d say right now it’s in the middle of a chilly snap which would be lucky to give London sleet and a cold spell maxes in London of 3-4c are more than standard. I think it’s fair to say if uppers were roughly 2C colder there’d be a lot more interest. Room for upgrades, this morning seems bit more positive to me with longer term prospects.

[nick sussex]

As frustrating as it might be regarding the 850 values I think it’s a case of a wait and see regarding any potential snow .

Surprises can pop up with the set up. 

After the low fills it’s likely a shortwave will move se on the eastern flank of the Atlantic block . 

That could provide more widespread interest . Detail this far out is difficult but the overall pattern is condusive to a prolonged period of below average temps with snow chances .

Not the depth of cold that we’d like to see but a whole lot better than what could have been served up at this time of the year .

[sheikhy]

25 minutes ago, IDO said:

The gefs at d12 are not yet conclusive for how the pattern develops from the third ridge post-d7. Certainly the op is the most progressive by d10 with the Greenland wedge, but it is not until d12 it gets a solid cluster in the ens. There are however maybe two more options with similar support...

d12 gefs> London> 

...the Atlantic high (rebounding at times) and the NW>SE flow. This still needs to be resolved. Still a solid 850's mean running through to d16 in my area, so an extended seasonal flow, with maybe after d12, some signs of a few members moving colder. There are the usual humbug runs mixed in of course.

Looking an interesting 10 days from Thursday and the door remains open in FI for further possibilities.

 

 

This is the most positive ive seen you in terms of forecasting cold weather ever!!!!!!!!i love it though mate!!

[Tim Bland]

Snow depth from ECM shows 15cm for parts of the south and widely 10cm+ its a slight shift east from yesterday... 

[mb018538]

43 minutes ago, Daniel* said:

You must be viewing different output to me. The day 6 projection looks fun to me on ECM, marginal aloft yes but there could be some surprise snowfall just about anywhere with this set up. Slacker winds and snow cover and it could become very cold on surface. We could generate our own cold in fact.

 

I agree @Daniel - with very low 500mb heights and light winds in play there, can't rule out snow.

I've not posted much recently as work has been a bit hectic, but have been intently watching and reading all the great posts from everyone! Nice to have a bit of buzz about the place in such gloomy times. Let's hope January delivers the goods.

[captaincroc]

42 minutes ago, Joe Bloggs said:

No complaints about the 00z output from me. 
 

A blocked Atlantic across the board. Yes the cold air isn’t QUITE there for the period immediately after Christmas  but that could well get upgraded and anywhere with altitude, especially in the north, may strike it lucky. 
 

Normally at this stage, into FI, we’d be seeing signs of the ridge flattening with the Atlantic taking over. It’s really reassuring to see continued bouts of blocking continuing to crop up - a signal that this could be a fairly extended spell of below average temps if we’re lucky. 
 

It would be really beneficial for us if we could somehow get the synoptics to align to deliver some proper Arctic air (-10C at 850 hPa) at some stage. This would allow more surface cooling and could make a difference when it comes to more marginal events down the line. 
 

As for NWS’s comments about easterlies - yes these benefit the Pennines, but for large areas of the NW, especially closer to the Irish Sea, a deep cold convective WNW’ly can actually be our biggest snow maker - think December 2009. 
 

Definitely the most interesting model watching for a considerable time. Reminds me a bit of the run up to December 2009 when it looked consistently promising for days on end - the air was just that bit colder back then to give more guaranteed snow opportunities for lower elevations.
 

All in all it’s looking very good.   

I was only thinking I hadn't seen you in the forum for a while Joe...then you post! haha.  Fingers crossed for the next week or so. haha

[northwestsnow]

49 minutes ago, Daniel* said:

You must be viewing different output to me. The day 6 projection looks fun to me on ECM, marginal aloft yes but there could be some surprise snowfall just about anywhere with this set up. Slacker winds and snow cover and it could become very cold on surface. We could generate our own cold in fact.

 

Ice day in the SE !!

[northwestsnow]

49 minutes ago, Joe Bloggs said:

No complaints about the 00z output from me. 
 

A blocked Atlantic across the board. Yes the cold air isn’t QUITE there for the period immediately after Christmas  but that could well get upgraded and anywhere with altitude, especially in the north, may strike it lucky. 
 

Normally at this stage, into FI, we’d be seeing signs of the ridge flattening with the Atlantic taking over. It’s really reassuring to see continued bouts of blocking continuing to crop up - a signal that this could be a fairly extended spell of below average temps if we’re lucky. 
 

It would be really beneficial for us if we could somehow get the synoptics to align to deliver some proper Arctic air (-10C at 850 hPa) at some stage. This would allow more surface cooling and could make a difference when it comes to more marginal events down the line. 
 

As for NWS’s comments about easterlies - yes these benefit the Pennines, but for large areas of the NW, especially closer to the Irish Sea, a deep cold convective WNW’ly can actually be our biggest snow maker - think December 2009. 
 

Definitely the most interesting model watching for a considerable time. Reminds me a bit of the run up to December 2009 when it looked consistently promising for days on end - the air was just that bit colder back then to give more guaranteed snow opportunities for lower elevations.
 

All in all it’s looking very good.   

Morning Joe ...

Yes, Easterlies suit imby with being pretty much in the Pennines...

Its a whole host of other factors,dews being top of the list.

Of course North westrrlies would be just as good but for the Irish Sea modification.

Like you, I'm happy with the 00z runs...

Fwiw, the higher routes locally ( 300m and above well get a decent covering over the coming period)..

Pendle Hill up near Burnley at 500m should also do very well...

Fascinating viewing, hoping as many as pos see snow ...

[DavidS]

I’ve not been doing this model watching very long, so my experience is limited. But how often do we see the GEFS with the AO like this? The spread is wide, but one member is off the scale negative.

[Mr Frost]

Morning all

Quick summary/snapshots from the latest UKV from Christmas Eve into the early hours of the 27th. 

NW/N/NE Scotland snow showers early AM on Christmas Eve.

24/12: 03:00

 

The above green blob out in the North Sea is what could land in Eastern parts of England later on that day and deliver a wintry mix! (See chart below) 

12:00

 

25/12: 18:00

Wet evening/night for West/Central Scotland.

 

26/12: 18:00

More widespread soaking and windy for much of NW UK and parts of Ireland. 

 

27/12: 03:00

Our next batch of cold air is moving in from the NW - wintry showers with snowfall over high ground at this stage for favoured areas. 

 

03:00

As always the above charts all subject to much change/timing at this range! 

All the best to you all! 

Edited December 22, 2020 by Mr Frost

[chris55]

Here is the potential snow event on ECM at 168-192. Origin of low to the north, rather than over the Atlantic ridge which is better, though the feature does pick up some milder air as it moves into the Atlantic and dives south. Marginal in places, timing and modifications could mean lots of snow for some. 
 

To far out to be taken with any confidence but once again highlighting the potential of features producing snowfall once the main trough is established. 
 

[johnholmes]

It is a long time since I have seen such a meridional 500 mb chart prediction close to the UK.

NOAA 6-10 

Climate Prediction Center - 6-10 Day 500mb Outlook

WWW.CPC.NCEP.NOAA.GOV

 

And the 8-14 is pretty similar; one would imagine at some point in the next 2 weeks some very cold air is possible?

[Tim Bland]

8 minutes ago, chris55 said:

Here is the potential snow event on ECM at 168-192. Origin of low to the north, rather than over the Atlantic ridge which is better, though the feature does pick up some milder air as it moves into the Atlantic and dives south. Marginal in places, timing and modifications could mean lots of snow for some. 
 

To far out to be taken with any confidence but once again highlighting the potential of features producing snowfall once the main trough is established. 
 

It’s been showing for a few days now on both ECM runs. Trend over the last couple of runs is to shift the core of the heavy snow east slightly. It’s gone from Wales to the midlands in 2 days (sound familiar?) it will probably end up in East Anglia ️

[Chesil View]

10 minutes ago, johnholmes said:

It is a long time since I have seen such a meridional 500 mb chart prediction close to the UK.

NOAA 6-10 

Climate Prediction Center - 6-10 Day 500mb Outlook

WWW.CPC.NCEP.NOAA.GOV

 

And the 8-14 is pretty similar; one would imagine at some point in the next 2 weeks some very cold air is possible?

being a very level headed former professional meteorologist I think this is the closest JH gets to a ramp

Edited December 22, 2020 by Broadmayne blizzard