theweatheroutlook

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fairweather
19 December 2022 23:00:23
A fair bit of non-factual non scientific rubbish being spouted on here tonight, and not especially on one side or the other. The argument on whether the op on the 12z GFS hPa ensemble is an outlier or not needs closer analysis. Neither person has said on which precise date nor given their definition of an outlier, if they have one. I'm sure there is a specific test for these ensembles but outliers may already have been rejected mathematically anyway by the model, which would make sense because otherwise the mean would be invalidated. In my day we used something called a "Q" test which I can barely remember how to do now. The most extreme point on that run is on the 31st December where in fact the op is the coldest, but not by as much as another run is mild at that same point. Visually the mild one looks more like an outlier but you can't actually just say that.  My guess is that there is such a large sd at that point that most likely neither are outliers. 
The sensible ones will just say there is too much uncertainty to say after December 26th.
In any case, what is a cold run or a mild run? it seems to be in the eye of the beholder.  I think some on here say a mild run is anything that isn't severe cold. Surely we should define a mild run as one above the mean at the point of discussion and a cold run as one below the mean? Then again most of us are looking for snow so perhaps we should refine the definitions to a cold run being below -5C on the 850 hPa and from that to the mean as "cool". Such fun 😀
S.Essex, 42m ASL
+2
Narnia
19 December 2022 23:06:01
Roll on tomorrow morning!!
squish
19 December 2022 23:11:45
Indeed. Hopefully the rain will have stopped and my kitchen flooding by then!!  Funny as soon as the METO scaled down the weather warning the rain pepped up across the SW and is still lashing down (sorry off topic!)

18z interesting again,  as is all the output. A wintry period from 24 dec to 3rd Jan is just about on the cards but how wintry and exactly where is any one's guess
D.E.W on Dartmoor. 300m asl
squish
19 December 2022 23:18:42
The mid latitude high scenario (around days 8-10) has certainly been binned by GEFS
D.E.W on Dartmoor. 300m asl
Rob K
19 December 2022 23:29:24

As I had anticipated, massive back track from GFS and more in line with UKMO and ECM.  

Originally Posted by: moomin75 


Doesn't look like a "massive backtrack" to me, it seems like more of the same with a Greenland/Iceland high keeping it cold for most after a short mild interlude.

I sometimes wonder if other people are seeing different output from me. That GFS run would be one of the wintriest of the season some years.
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
+2
dagspot
19 December 2022 23:39:29


I sometimes wonder if other people are seeing different output

Originally Posted by: Rob K 


I can predict the user often by the post… 🤣Even more predictable than backtracks
Neilston 600ft ASL
+2
ballamar
19 December 2022 23:39:46

Doesn't look like a "massive backtrack" to me, it seems like more of the same with a Greenland/Iceland high keeping it cold for most after a short mild interlude.

I sometimes wonder if other people are seeing different output from me. That GFS run would be one of the wintriest of the season some years.

Originally Posted by: Rob K 


I suppose many have their agenda, the actual Synoptics are impressive just might not snow exactly where someone wants it! Tiresome really
Zubzero
20 December 2022 00:01:26

Doesn't look like a "massive backtrack" to me, it seems like more of the same with a Greenland/Iceland high keeping it cold for most after a short mild interlude.

I sometimes wonder if other people are seeing different output from me. That GFS run would be one of the wintriest of the season some years.

Originally Posted by: Rob K 



Why bother replying he's wrong more times then I've had hot dinners. 

The Excellent forecast from Alex D from the meto posted previously sums up the current situation perfectly. 

So many options on offer on the Ens from the GEFS Ecm and MOGREPS. It could go either way? But it's so much diffrent from the normal weather patterns, will be fascinating to watch and learn from how it transpires regardless of the final out come.
Gandalf The White
20 December 2022 00:28:02

A fair bit of non-factual non scientific rubbish being spouted on here tonight, and not especially on one side or the other. The argument on whether the op on the 12z GFS hPa ensemble is an outlier or not needs closer analysis. Neither person has said on which precise date nor given their definition of an outlier, if they have one. I'm sure there is a specific test for these ensembles but outliers may already have been rejected mathematically anyway by the model, which would make sense because otherwise the mean would be invalidated. In my day we used something called a "Q" test which I can barely remember how to do now. The most extreme point on that run is on the 31st December where in fact the op is the coldest, but not by as much as another run is mild at that same point. Visually the mild one looks more like an outlier but you can't actually just say that.  My guess is that there is such a large sd at that point that most likely neither are outliers. 
The sensible ones will just say there is too much uncertainty to say after December 26th.
In any case, what is a cold run or a mild run? it seems to be in the eye of the beholder.  I think some on here say a mild run is anything that isn't severe cold. Surely we should define a mild run as one above the mean at the point of discussion and a cold run as one below the mean? Then again most of us are looking for snow so perhaps we should refine the definitions to a cold run being below -5C on the 850 hPa and from that to the mean as "cool". Such fun 😀

Originally Posted by: fairweather 



The GEFS comprises a control run and 30 perturbations, none of which are excluded.

The Op run is referred to, correctly, as an outlier when it falls is outside the spread of the ensemble suite.

As for the meaning of ‘very mild’, ‘mild’, ‘cold’ or ‘very cold’, it should be relative to the normal for that location and time of the year. Right now, for London, the normal maximum is around 9c and the minimum around 5c. If the forecast was for a high of 5-6c I’d call that ‘cold’; if it was down around 2-3c I’d call that ‘very cold’.  For above normal, I’d call 11-12c ‘mild’ and 14c+ ‘very mild’.

As for the Xmas weather, I agree with you. Things are finely poised still but current output would favour mild for the far south and cold for much of Scotland, with something of a guessing game across the 400 odd miles between the two.
Location: South Cambridgeshire
130 metres ASL
52.0N 0.1E


+1
Gandalf The White
20 December 2022 00:29:57

I suppose many have their agenda, the actual Synoptics are impressive just might not snow exactly where someone wants it! Tiresome really

Originally Posted by: ballamar 



It isn’t a ‘massive backtrack’. There are some really tiresome comments and pretty mediocre pseudo analysis being posted; quite disappointing and not a patch on what we used to see in here.
Location: South Cambridgeshire
130 metres ASL
52.0N 0.1E


+3
Rob K
20 December 2022 01:08:32
18Z GEFS for London has removed the notable cold dip on the 27th/28th which we had a couple of runs ago, and the mean pretty well flatlines along the 0C mark for much of the run. (In fact flipping between the 12Z and 18Z graphs the mean is virtually identical)

But there is still huge scatter and from Boxing Day onwards pretty much anything between +10C and -10C at 850hPa is on the table.
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
bledur
20 December 2022 05:45:51

Doesn't look like a "massive backtrack" to me, it seems like more of the same with a Greenland/Iceland high keeping it cold for most after a short mild interlude.

I sometimes wonder if other people are seeing different output from me. That GFS run would be one of the wintriest of the season some years.

Originally Posted by: Rob K 



"Two men looked out from prison bars, one saw the mud, the other saw stars"😎
White Meadows
20 December 2022 07:32:07
Gfs Op tasty for the first few days of Jan.
ECM sees rise of the toppler. Haven’t seen one of those in a while. 
nsrobins
20 December 2022 07:37:10
Some classic blending going on in the NWP mixing bowl once again. Just as EC and UKM think about dropping those Euro heights and getting some of that cold air south, GEFS drop most of the hints they’ve been having of post Christmas freezes.
I can’t actually make a forecast for the coming weekend based on what’s been churned out these last few days.
Who’d be a weather forecaster? 😂
 
Neil
Fareham, Hampshire 28m ASL (near estuary)
Stormchaser, Member TORRO
Zubzero
20 December 2022 07:44:02
DEW
  • DEW
  • Advanced Member
20 December 2022 08:11:08
WX temp summary - all change since yesterday when the cold air was due to re-establish over Europe. Today's charts confirm the withdrawal of the 0C isotherm to the Baltic States and definitely mild air for nearly all of W Europe in week 1. Then in week 2 it withdraws even further, but to the north. Everywhere south of a line from Ukraine west to Ireland is mild, bar mountains ... but ... unusually cold in N Scandinavia and across to Iceland which was not shown yesterday. Just an echo of this in the Scottish Highlands. Rain/snow for countries bordering the Atlantic in both weeks (Britain was shown dry in week 2 but no longer) and there is also pptn up to the Baltic and down to the Adriatic which is new.

GFS Op - LPs moving NE in the area of the British Isles to link up with a persistent area of LP over Scandinavia, with arctic air being brought S/SW-wards on their northern flank, mainly into the N Atlantic, occasionally close to Scotland with the best prospects for a N-ly plunge covering the whole of Britain coming on Mon 2nd. For the record, LP centres are close to Britain 975 mb Rockall Wed 21st, 990mb Irish Sea Sat 24th, 980mb off SW Ireland Thu 29th (this moving to English Channel Sun 1st). Rise of pressure over England Thu 5th.

ECM - starts out like GFS but puts a substantial HP block in place 1035mb SW Ireland Fri 30th with any N-lies diverted down the N Sea

GEFS - In the S, briefly mild around Fri 23rd then from Sun 25th minimal agreement between ens members; mean close to norm (yesterday it was trending colder) but op and control sharply colder after Mon 2nd. Pptn most likely and heaviest about Fri 23rd and Tue 27th but present in most ens members from time to time throughout, esp in SW. In Scotland the mildness around 23rd barely registers and it is then unquestionably cold until just after Christmas, at which date chaos sets in as above, even then the control remains cold. Pptn heaviest on the same dates as the S implying a heavy snowfall for Christmas Eve esp for the W. 

An uncertain muddle subject to change without notice!
War does not determine who is right, only who is left - Bertrand Russell

Chichester 12m asl
+2
Retron
20 December 2022 08:14:20

Merry Christmas to me 🎅 

https://www.meteociel.fr/modeles/gfse_cartes.php?&ech=126&mode=2 
 

Originally Posted by: Zubzero 


https://www.meteociel.fr/modeles/gfs/royaume-uni/precipitations-hd/126h.htm 

(Zoomed in view, the larger-scale charts are far too coarse to use for pinpointing snow).

That reminds me, remember the GFS will show a snow signal even if there's a single flake of snow amongst the rain: none of the models handle sleet particularly well.
Leysdown, north Kent
backtobasics
20 December 2022 08:14:47
gfs stepping away from any idea of extending cold from Christmas eve and into new year, at least in the 0z.  ECM looks like giving average winter weather with a brief cold blast, dare I say toppler. 

There look to be some possibilities still for colder than average and snow, mainly up north but the 0zs don't appear to be on quite the same hymn sheet yet although they are closer.

good news for those with travel plans or those who just get fed up with the cold 😁
BJBlake
20 December 2022 08:20:36
It remains one of the most interesting run-ups to Christmas we have seen for decades: The battle of air masses is fascinating: The jet remains amplified and with a southerly push from that, against a northerly push from what is going on across the pond: The fight is like a finely balanced pair of weighing scales: It isn’t going to take much to push the sweet spot one way or the other across the the UK, like the centre mark of a tug of war.
The GFS Op seems to have the most consistency and about the ebb and flow: but it will be a real opportunity to compare the models and see which one handles and predicts the reality. Thus far the ECM seems to have done well IMO, but in times past the GFS has been the best at signalling longer term trends, not always the one we might want. The Ops of the last 36-48 hours have often been at variance to the averages, and the other models. These ops seem to focus on the north-south battle, whilst others bring in the Atlantic west to east flow after Christmas. I am as interested in this as much as the hoped for outcome for cold - especially as it is now horridly mucky weather, so in contrast to that beautiful frozen world of last Saturday and before, which was wonderful for walking in - no muddy paws to wipe from my faithful furry friend Tess of the Doodlevilles, and no muddy boots. 
Brecklands, South Norfolk 28m ASL
Zubzero
20 December 2022 08:29:42

https://www.meteociel.fr/modeles/gfs/royaume-uni/precipitations-hd/126h.htm 

(Zoomed in view, the larger-scale charts are far too coarse to use for pinpointing snow).

That reminds me, remember the GFS will show a snow signal even if there's a single flake of snow amongst the rain: none of the models handle sleet particularly well.

Originally Posted by: Retron 



Yeah they can be misleading, but one can dream never seen snowfall on the day itself, had 1 year 2010 that had snow on the ground. 
Not given up all hope quite yet for this year. That even makes a change as normally by now there is no chance in the models. 
Gandalf The White
20 December 2022 08:49:34

https://www.meteociel.fr/modeles/gfs/royaume-uni/precipitations-hd/126h.htm 

(Zoomed in view, the larger-scale charts are far too coarse to use for pinpointing snow).

That reminds me, remember the GFS will show a snow signal even if there's a single flake of snow amongst the rain: none of the models handle sleet particularly well.

Originally Posted by: Retron 



Indeed - and the complete lack of forecast lying snow confirms it will at best be a wet mess.  Still , beggars can’t be choosers, as they say.
Location: South Cambridgeshire
130 metres ASL
52.0N 0.1E


Ally Pally Snowman
20 December 2022 08:50:14
Bit of a switcheroo with the ensembles.  ECM now colder than GFS. 


UserPostedImage





UserPostedImage
 
Bishop's Stortford 85m ASL.
Gandalf The White
20 December 2022 08:54:31

It remains one of the most interesting run-ups to Christmas we have seen for decades: The battle of air masses is fascinating: The jet remains amplified and with a southerly push from that, against a northerly push from what is going on across the pond: The fight is like a finely balanced pair of weighing scales: It isn’t going to take much to push the sweet spot one way or the other across the the UK, like the centre mark of a tug of war.
The GFS Op seems to have the most consistency and about the ebb and flow: but it will be a real opportunity to compare the models and see which one handles and predicts the reality. Thus far the ECM seems to have done well IMO, but in times past the GFS has been the best at signalling longer term trends, not always the one we might want. The Ops of the last 36-48 hours have often been at variance to the averages, and the other models. These ops seem to focus on the north-south battle, whilst others bring in the Atlantic west to east flow after Christmas. I am as interested in this as much as the hoped for outcome for cold - especially as it is now horridly mucky weather, so in contrast to that beautiful frozen world of last Saturday and before, which was wonderful for walking in - no muddy paws to wipe from my faithful furry friend Tess of the Doodlevilles, and no muddy boots. 

Originally Posted by: BJBlake 



Good post and sums up the fascinating set up this week and into the Xmas period.  I’m also 100% with you on the uplifting effects of blue skies and lying snow; it’s one of the main reasons for wanting colder weather - to break up the otherwise dull and gloomy December/January period around the winter solstice.
Location: South Cambridgeshire
130 metres ASL
52.0N 0.1E


Rob K
20 December 2022 10:08:33
6Z GFS op run shifts the airmass boundary on Xmas Day northward quite a bit compared to the 00Z. It's starting to get into the realms of the high-res models now, and the WRF looked significantly colder for the big day on the 00Z run. Arpege less interested.
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

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