theweatheroutlook

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fairweather
04 December 2022 15:18:15
It looks pretty solid now that we are in for at least 10 days of below average if not cold temperatures. The risk of snow will always be around for somewhere during that period.
S.Essex, 42m ASL
fairweather
04 December 2022 15:23:36
This is going to feel significantly cold I think. Today the maximum temperature here was 6.0C, the lowest maximum since January! 
S.Essex, 42m ASL
Rob K
04 December 2022 15:41:02

I'm not sure either. If the boundary layer had warmed wouldn't that just show as higher 850 hPa? Don't know. But I was under the impression that the temp at the 850mb height is absolute. i.e -7C then is the same as -7C now. Could it be the effect of AGW at the nearer surface level, i.e  ground and SST's being a couple of degrees higher  due to later summers, milder autumns and few if any pre-Christmas frosts? I really don't know but agree with your perception.

Originally Posted by: fairweather 


That's what I meant by boundary layer - maybe not the right terminology but I meant the near surface air. 

PS I've just been doing a few jobs in the garden and it feels absolutely bitter despite being 5C. Just shows how used we have got to very mild weather. 
Yateley, NE Hampshire, 73m asl
"But who wants to be foretold the weather? It is bad enough when it comes, without our having the misery of knowing about it beforehand." — Jerome K. Jerome
Gandalf The White
04 December 2022 15:59:37

Here's a vaguely model related question. If you look back at reanalyses charts for a lot of classic snow events you see very underwhelming 850mb temperatures, often only -5 or -6. Yet these days even when 850s are -7 or -8 or even lower we seem to overwhelmingly get rain. 

I know there is a lot more to it than 850mb temperatures but is there a reason for this? Has the boundary layer of air really warmed that much in the last few decades?

Originally Posted by: Rob K 



I thought it was more complicated than that?   The 850hPa value depends on the pattern - for a cold continental feed from the east/ESE you can get snow with 850hPa values only a couple of degrees below freezing, because the air mass betweeen that level and the ground is also very cold.  Conversely, in a showery northerly flow the surface layer has been modified and therefore lower 850hPa values are needed.  Then again, when you have frontal troughs moving into an cold air mass you again don't need such low 850hPa values; but it does depend on the nature of the frontal trough.
Location: South Cambridgeshire
130 metres ASL
52.0N 0.1E


Brian Gaze
04 December 2022 16:07:28
The notoriously accurate for the UK GFS snow depth charts suggest most of the UK will have a covering by Friday.

https://www.theweatheroutlook.com/twodata/gfs.aspx?run=12&charthour=108&chartname=uksnowdepth&chartregion=uk&charttag=Snow%20depth 


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Brian Gaze
Berkhamsted
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"I'm not socialist, I know that. I don't believe in sharing my money." - Gary Numan
doctormog
04 December 2022 16:08:18
That system in the Atlantic seems to be in a slightly different position with a different intensity once again on the latest GFS op run. I wonder what the effects will be down the line.
Aberdeen
Current conditions (personal WS) 
Gandalf The White
04 December 2022 16:15:29

That system in the Atlantic seems to be in a slightly difference position with a different intensity once again on the latest GFS op run. I wonder what the effects will be down the line.

Originally Posted by: doctormog 



Yes, I'm watching how that is being modelled on this run.  It was that plus the LP developing off the southern tip of Greenland, courtesy of the retrogression of the block, that was key.  So far, that deep LP is starting to move east but the block is a little stronger and there's no development near Greenland; will that steer the LP on a more southerly track?
Location: South Cambridgeshire
130 metres ASL
52.0N 0.1E


doctormog
04 December 2022 16:25:31
With high pressure edging down from the Arctic/Greenland-Norwegian Sea that would be very cold.

https://www.wetterzentrale.de/maps/GFSOPEU12_192_1.png  
Aberdeen
Current conditions (personal WS) 
Brian Gaze
04 December 2022 16:26:49
Interesting.

https://www.theweatheroutlook.com/twodata/gfs.aspx?run=12&charthour=210&chartname=mslp500&chartregion=na&charttag=500hPa%20GPDM 
 
Brian Gaze
Berkhamsted
TWO Buzz - get the latest news and views 
"I'm not socialist, I know that. I don't believe in sharing my money." - Gary Numan
Gandalf The White
04 December 2022 16:28:40

With high pressure edging down from the Arctic/Greenland-Norwegian Sea that would be very cold.

https://www.wetterzentrale.de/maps/GFSOPEU12_192_1.png  

Originally Posted by: doctormog 



High pressure is re-establishing to the east of Greenland and the LP systems appear to be stalling in mid-Atlantic on this run - out to T+216 now. The building blocks for an extended cold spell perhaps?
Location: South Cambridgeshire
130 metres ASL
52.0N 0.1E


Martybhoy
04 December 2022 16:29:59
My iPhone App now has me looking at 6 consecutive ice days from Wednesday.
200m above sea level
Rural East Ayrshire
Near to the village of Sorn
DEW
  • DEW
  • Advanced Member
04 December 2022 16:36:01

Here's a vaguely model related question. If you look back at reanalyses charts for a lot of classic snow events you see very underwhelming 850mb temperatures, often only -5 or -6. Yet these days even when 850s are -7 or -8 or even lower we seem to overwhelmingly get rain. 

I know there is a lot more to it than 850mb temperatures but is there a reason for this? Has the boundary layer of air really warmed that much in the last few decades?

Originally Posted by: Rob K 



My understanding was that it had a lot to do with the relative humidity of the lower few thousand feet of the atmosphere - call that a boundary layer if you like.

I think it was Bren who used to maintain that all precipitation started off as snow, it was just that it usually melted before it reached the ground. If the lower atmosphere is (very) dry, the precipitation is cooled enough by evaporation to persist as snow down to ground level.

That, of course, invites the question: do we get fewer dry E/NE lies than we used to? Speculatively, warmer oceans generate more activity and we get damp SW-lies pumped onto the western edge of continents instead.
War does not determine who is right, only who is left - Bertrand Russell

Chichester 12m asl
Gandalf The White
04 December 2022 16:36:04
GFS 12z out to T+240 now and the mild air has stalled just off the tip of Cornwall, with the cold air entrenched over the country.
Location: South Cambridgeshire
130 metres ASL
52.0N 0.1E


ballamar
04 December 2022 16:38:37
Wow @GFS
Gandalf The White
04 December 2022 16:39:22

My understanding was that it had a lot to do with the relative humidity of the lower few thousand feet of the atmosphere - call that a boundary layer if you like.

I think it was Bren who used to maintain that all precipitation started off as snow, it was just that it usually melted before it reached the ground. If the lower atmosphere is (very) dry, the precipitation is cooled enough by evaporation to persist as snow down to ground level.

That, of course, invites the question: do we get fewer dry E/NE lies than we used to? Speculatively, warmer oceans generate more activity and we get damp SW-lies pumped onto the western edge of continents instead.

Originally Posted by: DEW 



That was something I read/learned many years ago and certainly holds for temperate latitudes, AFAIK.   As you say, and as I suggested earlier, it depends on the characteristics of the air mass below cloud level as to whether the snow survives to the surface.  That, as we have discussed often, also depends on the intensity of the precipitation (which cools the air and drives the snow level down towards the surface).
Location: South Cambridgeshire
130 metres ASL
52.0N 0.1E


doctormog
04 December 2022 16:42:09
If this particular op run comes to fruition our energy network could be sorely tested, not to mention the issues with heating costs. I suspect it is one of the more extreme options. 
Aberdeen
Current conditions (personal WS) 
squish
04 December 2022 16:48:07
ICON/GEM and UKMO all look pretty solid...and the 12z GFS...well !😊
D.E.W on Dartmoor. 300m asl
Ally Pally Snowman
04 December 2022 16:52:11
Well the GFS 12z is a real beauty.  Looks like cold locked in right to day 16. Plenty of ensembles have done this recently so an Op was probably going to do it at some point.
 
Bishop's Stortford 85m ASL.
nsrobins
04 December 2022 16:52:22
Can someone explain what the GFS just did there as I'm losing the plot lol. Great fun 🤩 
Neil
Fareham, Hampshire 28m ASL (near estuary)
Stormchaser, Member TORRO
doctormog
04 December 2022 16:54:27

Can someone explain what the GFS just did there as I'm losing the plot lol. Great fun 🤩 

Originally Posted by: nsrobins 



No, sorry. 🤣
Aberdeen
Current conditions (personal WS) 
Brian Gaze
04 December 2022 17:05:50
Decent snow event at t+357. I've added to my diary.

https://www.theweatheroutlook.com/twodata/gfs.aspx?run=12&charthour=357&chartname=preciptype&chartregion=uk&charttag=Precip%20type 
Brian Gaze
Berkhamsted
TWO Buzz - get the latest news and views 
"I'm not socialist, I know that. I don't believe in sharing my money." - Gary Numan
Taylor1740
04 December 2022 17:06:05
That GFS run is crazy, highly unlikely to verify but if it did I would think we'd be looking at another sub zero December CET.
NW Leeds - 150m amsl
Gandalf The White
04 December 2022 17:10:03

Can someone explain what the GFS just did there as I'm losing the plot lol. Great fun 🤩 

Originally Posted by: nsrobins 



Perhaps Elon Musk has bought GFS and the programmers have been given free rein to express themselves?

😉
😁
Location: South Cambridgeshire
130 metres ASL
52.0N 0.1E


Rob K
04 December 2022 17:29:00
GEFS mean looks a fair bit. colder than the 6Z out to 240 hours. 
Yateley, NE Hampshire, 73m asl
"But who wants to be foretold the weather? It is bad enough when it comes, without our having the misery of knowing about it beforehand." — Jerome K. Jerome
scillydave
04 December 2022 17:34:09
That chart gives a solid 36 hours of snow in my back yard. Proper Westcountry blizzard ala 1978
Currently living at roughly 65m asl North of Cowbridge in the Vale of Glamorgan.

Formerly of, Birdlip, highest village in the Cotswolds and snow heaven in winter; Hawkinge in Kent - roof of the South downs and Isles of Scilly, paradise in the UK.

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