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Brian Gaze
26 December 2023 09:43:30
ECM ENS looks less keen on a colder period, but the stamps are very mixed indeed.

https://www.theweatheroutlook.com/twodata/ecmhrens.aspx 
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
tallyho_83
26 December 2023 12:11:47
At least Aviemore and Scottish Highlands will have a good "dump!" Of snow looking at Ens.

https://wetterzentrale.de/en/show_diagrams.php?geoid=51090&model=gfs&var=203&run=06&lid=ENS&bw=1 
Home Location - Kellands Lane, Okehampton, Devon (200m ASL)
---------------------------------------
Sean Moon
Magical Moon
www.magical-moon.com


nsrobins
26 December 2023 12:55:43

Suffice to say I'll not be paying too much attention to today's model output (as was the case with yesterday's), and it's no surprise to see "blocky" output.

The acid test will be whether the blocking persists in tomorrow's output - if it does, maybe, just maybe, the annual Christmas mirage will reflect reality for once!

(I wouldn't expect to see "holy grail" charts for another week, as the strat slowdown/reversal isn't for another week or so - to see them in the timeframes being shown today would be very unusual.)

Originally Posted by: Retron 



Sage council, but the current flavour appearing of HLB is apparently trop lead not strat led, which if true might well be reinforced when the reversal (70% chance as it stands) filters down. 
After a VAR delay in the run up to Christmas, the game has now restarted.
Neil
Fareham, Hampshire 28m ASL (near estuary)
Stormchaser, Member TORRO
nsrobins
26 December 2023 12:57:55
https://www.theweatheroutlook.com/twodata/gefs.aspx?run=na&lg=850&lglocation=london&charthour=006&chartname=ps_500hpa&chartregion=na-region&p=1&charttag=PS%20500hPa%20(GPDM) 

A mean of -5 and a growing cluster at -10 is the starting pistol for me for the chase to an easterly driven cold spell.
Neil
Fareham, Hampshire 28m ASL (near estuary)
Stormchaser, Member TORRO
Rob K
26 December 2023 13:01:05

https://www.theweatheroutlook.com/twodata/gefs.aspx?run=na&lg=850&lglocation=london&charthour=006&chartname=ps_500hpa&chartregion=na-region&p=1&charttag=PS%20500hPa%20(GPDM) 

A mean of -5 and a growing cluster at -10 is the starting pistol for me for the chase to an easterly driven cold spell.

Originally Posted by: nsrobins 



Despite an uninspiring op run the GEFS mean is slightly colder on the 6Z than 0Z.
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
CField
26 December 2023 16:52:12
For 6 degrees cold rain lovers the 12z run looks fulfilling....heights from sw coming into play at the very end ....
Favourite snowstorm
Famous channel low
Dec 31st 1978
Hastings East Sussex
Foot of level snow severe drifting
Next day max temp -4 degrees Celsius
Retron
26 December 2023 17:37:43
A marked downgrade in terms of the cold on the 12z GFS op run. Can't say that was unexpected, but hopefully just a blip...

0z:
https://ukwct.org.uk/weather/temp4-3.png 
UserPostedImage

12z:
http://wxmaps.org/pix/temp4.png 
UserPostedImage
Leysdown, north Kent
Brian Gaze
26 December 2023 19:12:52
The cold signal >05/01 looks weaker on the GEFS 12Z. There may well be more volatility in the output at the moment for there reasons discussed. Personally, I'd give it another 48 hours before putting much stock in how things will develop during the first week or two of January.

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
doctormog
26 December 2023 19:19:04

The cold signal >05/01 looks weaker on the GEFS 12Z. There may well be more volatility in the output at the moment for there reasons discussed. Personally, I'd give it another 48 hours before putting much stock in how things will develop during the first week or two of January.

UserPostedImage

Originally Posted by: Brian Gaze 



Absolutely! Having said that the ECM 12z op run is interesting.
Brian Gaze
26 December 2023 19:33:33

Absolutely! Having said that the ECM 12z op run is interesting.

Originally Posted by: doctormog 



The general pattern still looks like one which could bring snow to the north at times, particularly over high ground. The risk in the south isn't zero, but it is considerably lower. 
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
DPower
26 December 2023 21:27:40
No surprise to see a much less amplified pattern post t144 due I think to Christmas and boxing day lack of data ( could be talking rubbish mind). Also no surprise to see a large reduction in strat reversals on the eps and gefs today. 
Hoping to see a return to more amplified patterns again by tomorrow afternoon runs. If a qtr is to be seen then I would fully expect to see the models showing it in the further reaches of the runs.
Quantum
27 December 2023 03:30:15
One hell of an upgrade on the ICON0z
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.
Zubzero
27 December 2023 05:47:44

One hell of an upgrade on the ICON0z

Originally Posted by: Quantum 



Maybe for your back garden? For the majority the rain might be a bit colder 😉 
Retron
27 December 2023 06:11:25
I have to say I'm relieved to see that there hasn't been any great change in the model output this morning - we're back to normalish data levels and the blocking remains. Overnight the ECM stratosphere charts updated and, significantly, for the first time they're showing a mean reversal, i.e. a major SSW.

Assuming that remains the case, I'm hopeful of some truly blockbuster charts appearing over the weekend!

https://charts.ecmwf.int/products/extended-zonal-mean-zonal-wind?area=nh&base_time=202312260000 
Leysdown, north Kent
Heavy Weather 2013
27 December 2023 06:32:12

I have to say I'm relieved to see that there hasn't been any great change in the model output this morning - we're back to normalish data levels and the blocking remains. Overnight the ECM stratosphere charts updated and, significantly, for the first time they're showing a mean reversal, i.e. a major SSW.

Assuming that remains the case, I'm hopeful of some truly blockbuster charts appearing over the weekend!

https://charts.ecmwf.int/products/extended-zonal-mean-zonal-wind?area=nh&base_time=202312260000 

Originally Posted by: Retron 



I hope this continues. We are so overdue a really cold January. Let’s hope we finally hit the jackpot
Mark
Beckton, E London
Less than 500m from the end of London City Airport runway.
Retron
27 December 2023 06:56:04
I think after several years it's time for one of these - ensemble watch is back! 😀

For those who've not seen this before, I've been doing these on occasion since 2009. The picture in the background is from 2005, the last great easterly.
The way they work is simple: I take the Meteociel GEFS charts for London and count the number of members that go below -10C at 850 for London. (-10 was chosen as it's almost certain anything that falls would be snow).
This gets updated once or twice a day until either the cold spell arrives, or it fizzles out. In this case, I'm looking at the 6th January for the onset - so I'll keep updating these for several days yet.

One of the other requirements for me to do these is a personal forecast chance of at least 66% of a decent cold spell coming off, so they're not often seen!

https://ukwct.org.uk/weather/enswatch.jpg 
UserPostedImage
Leysdown, north Kent
Ally Pally Snowman
27 December 2023 06:56:17
Good London GEFS this morning.  If its on the money the cold spell starts about the 6th.


UserPostedImage

 
Bishop's Stortford 85m ASL.
Heavy Weather 2013
27 December 2023 07:16:13

I think after several years it's time for one of these - ensemble watch is back! 😀

For those who've not seen this before, I've been doing these on occasion since 2009. The picture in the background is from 2005, the last great easterly.
The way they work is simple: I take the Meteociel GEFS charts for London and count the number of members that go below -10C at 850 for London. (-10 was chosen as it's almost certain anything that falls would be snow).
This gets updated once or twice a day until either the cold spell arrives, or it fizzles out. In this case, I'm looking at the 6th January for the onset - so I'll keep updating these for several days yet.

One of the other requirements for me to do these is a personal forecast chance of at least 66% of a decent cold spell coming off, so they're not often seen!

https://ukwct.org.uk/weather/enswatch.jpg 
UserPostedImage

Originally Posted by: Retron 



OMG. It’s back. This is a very good sign.
Mark
Beckton, E London
Less than 500m from the end of London City Airport runway.
DEW
  • DEW
  • Advanced Member
27 December 2023 08:06:14
WX summary consistent in showing a cooling for W Europe from mild in week 1 to something near norm in week 2, maybe not as much cooling as in yesterday's 00z; but the major change this morning is the expansion of extreme cold weather all the way from Norway through Finland to C Europe. This is the first time this year that such an extensive area has appeared; previously there were only patches and only in the far N.  Pptn much as yesterday, week 1 for Britain, Atlantic coasts and across the S Baltic; this whole area moving S-wards into, N Spain, S France and across to the Balkans, plus some separately hanging around in the Norwegian and North Seas.

GFS Op - Storm Gerrit is multi-centred 975mb Hebrides and two more centres on the Atlantic, coalescing and passing across Scotland (more slowly than shown yesterday) to 980mb off S Norway Fri 29th with N/NW-lies for Britain. Next LP, also looking stormy, 965mb Donegal Sat 30th crossing N England to N Sea the following day with more N-lies. Then there is another 970mb Kerry Tue 2nd but this first moving N-wards before in conjunction with a drop in pressure off Spain producing a shallow trough N-S Sat 6th covering Britain. Eventually this makes contact with the semi-permanent LP in the Baltic (which has been absent for a spell further E bringing  in the colder weather referred to above) and brings in NE-lies Thu 11th. 

ECM - similar to GFS until Thu 4th when the N-S trough referred to above makes an early appearance, making way for a new Lp from the Atlantic 980mb off NW Ireland threatening to bring E/NE winds at least for Scotland.

GEFS - A decline in the mean temp from near normal temp to cool/cold by Fri 12th with a couple of interruptions. By Fri 12th the majority of ens members incl op & control are cooler than mean which is only being held up by just a few rather mild members. Heaviest pptn week beginning Sun 30th in S or from today in N; Scotland looking drier and indeed snowier later but rain persisting to some extent in the S. 

Snow row figures suggest a moderate chance of snow at sea level in N Scotland. the synoptics above suggest that hills further S will get more.
War does not determine who is right, only who is left - Bertrand Russell

Chichester 12m asl
Ally Pally Snowman
27 December 2023 09:57:35
Not as good as the GEFS but going in the right direction.  

UserPostedImage
Bishop's Stortford 85m ASL.
The Beast from the East
27 December 2023 10:13:26

Not as good as the GEFS but going in the right direction.  

Originally Posted by: Ally Pally Snowman 



Still not convinced about this cold spell. Remember last time! 
Before that a nasty storm to end the year and start the new one. I assume the fireworks will be cancelled hopefully
"We have some alternative facts for you"
Kelly-Ann Conway - special adviser to the President
nsrobins
27 December 2023 10:26:38

I think after several years it's time for one of these - ensemble watch is back! 😀

https://ukwct.org.uk/weather/enswatch.jpg 
UserPostedImage

Originally Posted by: Retron 



Already 12 members sub -10 (at some point in their track). I think this is a simple but decent metric to gauge the likelihood of an impending cold spell and it's nice to see it back on the forum.
My current thinking is a 60% chance of a robust E/NE flow and associated wintry hazards by 6th Jan - which is as we know at the extreme end of the unreliable range (the caveat being the drivers and connections etc seem to be falling into place).
Neil
Fareham, Hampshire 28m ASL (near estuary)
Stormchaser, Member TORRO
doctormog
27 December 2023 10:45:11
The GFS 06z op continues with that theme.
The Beast from the East
27 December 2023 10:54:14
sends New year storm further north, better news for the south but will be wet
 
"We have some alternative facts for you"
Kelly-Ann Conway - special adviser to the President
Retron
27 December 2023 11:06:58
A genuine "snow on the ground for most" run... good to see, even if the the widespread snow only happens right at the end.

https://images.meteociel.fr/im/81/25381/gfs_16_366glh6.png 
UserPostedImage
Leysdown, north Kent

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