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doctormog
02 February 2024 07:42:06

https://www.theweatheroutlook.com/charts/gefs/gefsenswind_10mb60.png?w=800&colors=128 

Hi this is my first post.  Does this graph indicate a possible SSW?  Thank you.

Originally Posted by: KLammond 



Welcome! I think it indicates that another SSW is possible, although I would not say “probable” at this stage.

Edit: Darren beat me to it!
Aberdeen
Current conditions (personal WS) 
+2
nsrobins
02 February 2024 07:43:01
GEM is the sort of evolution I’m looking for 😂😂
Neil
Fareham, Hampshire 28m ASL (near estuary)
Stormchaser, Member TORRO
+1
The Dub Version
02 February 2024 07:55:57
A bit more confident this morning. Normally it's a case of let's get the cold in first....however last few spells and in previous years, its a case of let's get the PPN in as well.
 
Berkshire
Ally Pally Snowman
02 February 2024 08:03:50

Hi, welcome to TWO!

You're right - the graph has a few members showing a major SSW (reversal), including the operational run. Possible, but unlikely is how I'd sum that up.

The ECM ensembles show a similar picture:

https://charts.ecmwf.int/products/extended-zonal-mean-zonal-wind?area=nh&base_time=202402010000 

Originally Posted by: Retron 



I can't remember a winter where the Strat has taken such a battering. We've had a couple of nr misses and a SSW already. Seems unusual. 

 
Bishop's Stortford 85m ASL.
Brian Gaze
02 February 2024 08:14:16

I can't remember a winter where the Strat has taken such a battering. We've had a couple of nr misses and a SSW already. Seems unusual. 

 

Originally Posted by: Ally Pally Snowman 



I agree. The addendum is that despite the battering it has taken and some of the other background signals being favourable, this winter remains snowless in most of the UK.
Brian Gaze
Berkhamsted
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"I'm not socialist, I know that. I don't believe in sharing my money." - Gary Numan
+3
ballamar
02 February 2024 08:22:17

I agree. The addendum is that despite the battering it has taken and some of the other background signals being favourable, this winter remains snowless in most of the UK.

Originally Posted by: Brian Gaze 



just been saving itself up for February !
+2
Brian Gaze
02 February 2024 08:25:29
Here's a snapshot of the GEFS 850hPa temp tracker for London. (Full version here https://www.theweatheroutlook.com/tracker/tmp850  with login)

UserPostedImage
Brian Gaze
Berkhamsted
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"I'm not socialist, I know that. I don't believe in sharing my money." - Gary Numan
Brian Gaze
02 February 2024 08:28:57
Here's the GFS 00Z snow depth chart for 11/02. I've long suspected the value it uses for snow density has a tendency to be too low for the UK. Therefore, I'm going to add a version (hopefully in the next couple of days) of this chart which uses a higher value to see how it performs in comparison. 

UserPostedImage
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
+2
The Dub Version
02 February 2024 08:39:00

I agree. The addendum is that despite the battering it has taken and some of the other background signals being favourable, this winter remains snowless in most of the UK.

Originally Posted by: Brian Gaze 



I cant even remember seeing back edge snow any more in more than 20 years, as a front cleared.

It was oh so common in the 80s
 
Berkshire
Quantum
02 February 2024 08:58:58
I'd remind people to not yet get too excited by this. One very likely scenartio, hinted by the ECM is the low overdevelops before it gets to the UK. If it occludes then mild air will mix in north of the triple point and the airmass gradients across the fronts will reduce. If that happens snow will be restricted to northern scotland and probably only high ground. The GFS scenario or the GEM scenario which develop the low less are also plausible but so is the low being less developed which will essentially mean no snow at all and a northerly toppler. Uncertainty is very high, much higher than for the last cold spell which didn't deliver for most.

On the plus side, we do come reasonably close to the reliable timeframe by the 12Z set today. High res models should get this fully in range by tommorow.

EDIT: I should add that the overdevelopment scenario is much more common on the ensembles than it should be given the OPs; yesterday the OP was an outliar so the high res models do seem to be picking up on some tiny detail that limits development. I do worry though that we could very easily revert to the overdevelopment scenario which was overwhelmingly favoured on the GEFS yesterday.

 
2023/2024 Snow days (approx 850hpa temp):
29/11 (-6), 30/11 (-6), 02/12 (-5), 03/12 (-5), 04/12 (-3), 16/01 (-3), 18/01 (-8), 08/02 (-5)

Total: 8 days with snow/sleet falling.

2022/2023 Snow days (approx 850hpa temp):

18/12 (-1), 06/03 (-6), 08/03 (-8), 09/03 (-6), 10/03 (-8), 11/03 (-5), 14/03 (-6)

Total: 7 days with snow/sleet falling.

2021/2022 Snow days (approx 850hpa temp):

26/11 (-5), 27/11 (-7), 28/11 (-6), 02/12 (-6), 06/01 (-5), 07/01 (-6), 06/02 (-5), 19/02 (-5), 24/02 (-7), 30/03 (-7), 31/03 (-8), 01/04 (-8)
Total: 12 days with snow/sleet falling.
+1
Quantum
02 February 2024 09:05:04

I cant even remember seeing back edge snow any more in more than 20 years, as a front cleared.

It was oh so common in the 80s
 

Originally Posted by: The Dub Version 



It inutitively makes sense though. In order to get backend snow you need cold air to advect in very very strongly and when that happens it dries out and weakens the precipitation.

A far easier way to get snow is for the cold front to start stalling and develop a wave (secondary low) on it and 'turn into a warm front' so to speak. That scenario produces snow quite efficiently.
 
2023/2024 Snow days (approx 850hpa temp):
29/11 (-6), 30/11 (-6), 02/12 (-5), 03/12 (-5), 04/12 (-3), 16/01 (-3), 18/01 (-8), 08/02 (-5)

Total: 8 days with snow/sleet falling.

2022/2023 Snow days (approx 850hpa temp):

18/12 (-1), 06/03 (-6), 08/03 (-8), 09/03 (-6), 10/03 (-8), 11/03 (-5), 14/03 (-6)

Total: 7 days with snow/sleet falling.

2021/2022 Snow days (approx 850hpa temp):

26/11 (-5), 27/11 (-7), 28/11 (-6), 02/12 (-6), 06/01 (-5), 07/01 (-6), 06/02 (-5), 19/02 (-5), 24/02 (-7), 30/03 (-7), 31/03 (-8), 01/04 (-8)
Total: 12 days with snow/sleet falling.
Retron
02 February 2024 09:19:43

It inutitively makes sense though. In order to get backend snow you need cold air to advect in very very strongly and when that happens it dries out and weakens the precipitation.
 

Originally Posted by: Quantum 


In today's climate, yes. In the old days - not so much, you didn't need a such a depth of anomalous cold to do it. You're too young to have seen the early to mid 80s, and believe you me - you really missed out!

I'm sure the same could be said of us 80s kids by those who were around in the 60s, mind you. 😂
Leysdown, north Kent
Quantum
02 February 2024 09:22:12
I think what's going on here is that in principle we have a zonal pattern albeit a somewhat weak, unusual one with a deep high over the arctic and the tropospheric PV located over scandanavia rather than Canada. Alone this causes a northerly toppler at most, but the other factor is a scrap of PV that breaks away from the main vortex over the Newfoundland area and sluggishly moves eastward. The main jet stream is to the north of this cold core feature so the surface low struggles to intensify.

But this scrap of tropospheric PV rejoins with the main polar vortex as the surface LP hits the UK which makes conditions favourable for intensification as the surface low ends up near the jetstream. Its how early or late this merger occurs that seems to impact conditions, but its also a bit more than that. GEM illustrates a scenario where the LP doesn't really develop at all after the merger because the LP asociated with the main polar vortex develops instead since the surface LP is closer to the jet.

Its very complicated, and somewhat reminiscant of many Northeasters in the US where two cold core troughs, one from the midwest and one from the carribean merge causing wildly dirvergent snow forecasts as models struggle to handle this merging process and how the surface LP is affected by it.
 
2023/2024 Snow days (approx 850hpa temp):
29/11 (-6), 30/11 (-6), 02/12 (-5), 03/12 (-5), 04/12 (-3), 16/01 (-3), 18/01 (-8), 08/02 (-5)

Total: 8 days with snow/sleet falling.

2022/2023 Snow days (approx 850hpa temp):

18/12 (-1), 06/03 (-6), 08/03 (-8), 09/03 (-6), 10/03 (-8), 11/03 (-5), 14/03 (-6)

Total: 7 days with snow/sleet falling.

2021/2022 Snow days (approx 850hpa temp):

26/11 (-5), 27/11 (-7), 28/11 (-6), 02/12 (-6), 06/01 (-5), 07/01 (-6), 06/02 (-5), 19/02 (-5), 24/02 (-7), 30/03 (-7), 31/03 (-8), 01/04 (-8)
Total: 12 days with snow/sleet falling.
David M Porter
02 February 2024 09:23:05

I agree. The addendum is that despite the battering it has taken and some of the other background signals being favourable, this winter remains snowless in most of the UK.

Originally Posted by: Brian Gaze 



I think a lot of the reason for that has been the presence of HP to the south of the UK for a lot of the winter thus far. It was said by one or two people here before Christmas that those heights to the south, as we are seeing at the moment and for much of the time during December, would likely be the biggest obstacle to getting widespread cold and snowfalls and so it has proved.
Lenzie, Glasgow

"Let us not take ourselves too seriously. None of us has a monopoly on wisdom, and we must always be ready to listen and respect other points of view."- Queen Elizabeth II 1926-2022
Brian Gaze
02 February 2024 09:47:01

I think a lot of the reason for that has been the presence of HP to the south of the UK for a lot of the winter thus far. It was said by one or two people here before Christmas that those heights to the south, as we are seeing at the moment and for much of the time during December, would likely be the biggest obstacle to getting widespread cold and snowfalls and so it has proved.

Originally Posted by: David M Porter 



I said that. I also provided evidence which shows that pressure anomalies to the south of the UK have increased in recent decades. 
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
The Dub Version
02 February 2024 09:49:14

In today's climate, yes. In the old days - not so much, you didn't need a such a depth of anomalous cold to do it. You're too young to have seen the early to mid 80s, and believe you me - you really missed out!

I'm sure the same could be said of us 80s kids by those who were around in the 60s, mind you. 😂

Originally Posted by: Retron 



I remember several occasions, when rain fronts moved through , sudden drop in temps, heavy wet snow, then snow, then clearing to heavy showers with skies darkening from the north all the time with rain/snow showers and sunshine.

Thats when northerlies nearly always delivered , even all the way down south.

 
Berkshire
+1
CField
02 February 2024 10:13:18

I remember several occasions, when rain fronts moved through , sudden drop in temps, heavy wet snow, then snow, then clearing to heavy showers with skies darkening from the north all the time with rain/snow showers and sunshine.

Thats when northerlies nearly always delivered , even all the way down south.

 

Originally Posted by: The Dub Version 

Plenty of snow turn to rain events aswell....
Favourite snowstorm
Famous channel low
Dec 31st 1978
Hastings East Sussex
Foot of level snow severe drifting
Next day max temp -4 degrees Celsius
+1
Quantum
02 February 2024 10:13:27
UserPostedImage
(full image: https://snipboard.io/JSqpyh.jpg)

Merger is quite clear here. Note the outflow channel (red arrow); when the LP hits that we get rapid intensification. There is some genuine potential here for a quite significant snow event if  the LP hits this upper level outflow channel over the UK
 
2023/2024 Snow days (approx 850hpa temp):
29/11 (-6), 30/11 (-6), 02/12 (-5), 03/12 (-5), 04/12 (-3), 16/01 (-3), 18/01 (-8), 08/02 (-5)

Total: 8 days with snow/sleet falling.

2022/2023 Snow days (approx 850hpa temp):

18/12 (-1), 06/03 (-6), 08/03 (-8), 09/03 (-6), 10/03 (-8), 11/03 (-5), 14/03 (-6)

Total: 7 days with snow/sleet falling.

2021/2022 Snow days (approx 850hpa temp):

26/11 (-5), 27/11 (-7), 28/11 (-6), 02/12 (-6), 06/01 (-5), 07/01 (-6), 06/02 (-5), 19/02 (-5), 24/02 (-7), 30/03 (-7), 31/03 (-8), 01/04 (-8)
Total: 12 days with snow/sleet falling.
BJBlake
02 February 2024 10:19:45

In today's climate, yes. In the old days - not so much, you didn't need a such a depth of anomalous cold to do it. You're too young to have seen the early to mid 80s, and believe you me - you really missed out!

I'm sure the same could be said of us 80s kids by those who were around in the 60s, mind you. 😂

Originally Posted by: Retron 



Yes - you are sooo right here. The 60s were so very snowy at times. I remember being at school in 1969, and whenever it precipitated it was snow, even when it didn’t settle, and wow, when it did - it was deep, and this was in the Deep South - Nuthurst, West Sussex.
Brecklands, South Norfolk 28m ASL
+1
Ally Pally Snowman
02 February 2024 10:22:28
Well the GFS 6z has a big dump of snow next Friday for Wales and Midlands.  
Bishop's Stortford 85m ASL.
nsrobins
02 February 2024 10:49:41
GFS 06Z OP looks like delivering a bit of love in time for Valentines Day ;)
One option, one run, likely all gone by the 12Z - but (huge caveat) the UKMO long range and EC46 anomalies have been pointing to something akin to a Scandy high for a few days now.
Will 'winter' have a last hurrah?
Neil
Fareham, Hampshire 28m ASL (near estuary)
Stormchaser, Member TORRO
Hippydave
02 February 2024 11:03:34
Something for everyone seemingly on the 6z GFS op run.

Snow in parts north as cold air pushes south.
LP running across the Midlands with snow on the northern flank.
Less cold/chilly HP interlude followed by a strong cold easterly. 

Part 1 is IMO very likely and essentially in the semi reliable.
Part 2 is uncertain as it depends on LP track. I think it's more likely that will be over the UK somewhere this time round as different setup to the Jan LP tease but as others have said it really depends on how the LP deepens/interacts with the jet and it's too far out to be confident in that. Somewhere from the M4 to southern Scotland could see snow as it stands I think but I'd punt it as somewhere between northern England and Wales/Midlands. 
Part 3, will wait for the ens and subsequent runs but a very low chance as it stands. It shows what can happen though and with some of the background drivers allegedly being favourable and Easterlies a little easier to come by in mid to late Feb as the jet dies down it's something to keep an eye on. 


 
Home: Tunbridge Wells
Work: Tonbridge
Ally Pally Snowman
02 February 2024 11:17:53
Yep an old school 80s classic easterly on the 6z. Outside bet atm but mid/ late February looking like it could be the best of this winter at least.
 
Bishop's Stortford 85m ASL.
tallyho_83
02 February 2024 11:35:47
06z Op run goes for a BFTE and almost a repeat of storm Emma bringing blizzard conditions to the south of country @ +342z:

If Only....
UserPostedImage
Home Location - Kellands Lane, Okehampton, Devon (200m ASL)
---------------------------------------
Sean Moon
Magical Moon
www.magical-moon.com


+1
Brian Gaze
02 February 2024 11:51:08
Here we go...

Here's the snow depth using the default GFS parameter:

UserPostedImage


Here's the snow depth for the same time after setting snow density to be 400 kg/m2.

UserPostedImage
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
+1

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