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moomin75
28 November 2023 17:47:45
As expected, the 12z GFS run is a HUGE outlier.
On we go!
Witney, Oxfordshire
100m ASL
DEW
  • DEW
  • Advanced Member
28 November 2023 18:09:25
WX temp charts unlike this morning when the freezing weather was due to retreat to Poland, now show a full-on blast in week 2 all the way to the Atlantic coasts. Britain is on the next coldest level, but not freezing except in the Highlands. 
http://www.wxmaps.org/pix/temp4  
War does not determine who is right, only who is left - Bertrand Russell

Chichester 12m asl
Rob K
28 November 2023 18:25:35

I'm starting to think a human somewhere in GFS and ECM towers talk to each other and deliberately put out these runs manually just to toy with us all.
I am not falling for the 12z GFS one jot. A clear Outlier surely.

Originally Posted by: moomin75 



Looking at the postage stamps it's not totally without support. In the minority though. https://www.meteociel.fr/cartes_obs/gens_panel.php?modele=0&mode=1&ech=276&size= 
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
Taylor1740
28 November 2023 18:59:04

As expected, the 12z GFS run is a HUGE outlier.
On we go!

Originally Posted by: moomin75 


now that is what you call an outlier. A crushing set of ensembles for cold weather fans!
NW Leeds - 150m amsl
+1
doctormog
28 November 2023 19:03:16

now that is what you call an outlier. A crushing set of ensembles for cold weather fans!

Originally Posted by: Taylor1740 


I’m not sure anyone had such high expectations in the day 10ish time range for those to be “crushed”. The uncertainty is high in that range and has been since this current cold spell came into the reliable time frame. 

I guess the GFS 12z op run may have been an outlier in some parts, here it is just one of the coldest option in “FI”.

UserPostedImage 

Beyond the cold or potentially wintriness in the next week or so it will be interesting to see how things evolve in early December. Very mild, average, cold? All options are on the table.
Aberdeen
Current conditions (personal WS) 
+1
Rob K
28 November 2023 19:09:58

now that is what you call an outlier. A crushing set of ensembles for cold weather fans!

Originally Posted by: Taylor1740 



The ensembles are a lot better than the 6Z. At least there are two or three other runs taking the same route as the op. On the 6Z there was not a sausage.
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
ballamar
28 November 2023 19:21:24
I don’t think the ECM and GFS at 240 are massively different just the location of the cold
+2
MBrothers
28 November 2023 19:25:35

now that is what you call an outlier. A crushing set of ensembles for cold weather fans!

Originally Posted by: Taylor1740 

a bit dramatic dear . 
Gandalf The White
28 November 2023 19:42:09

now that is what you call an outlier. A crushing set of ensembles for cold weather fans!

Originally Posted by: Taylor1740 



I have to assume that either you’re being unnecessarily dramatic or you’ve misunderstood the word ‘outlier’?

The Op is only a true outlier for a total of three days across the final seven days of the output, the rest of the time there is some support from the ensemble suite.  It hinges on whether the Op has the behaviour of the jet stream and the associated build of the Scandi high right.

Lack of support does not equal wrong, it just equals huge uncertainty.
Location: South Cambridgeshire
130 metres ASL
52.0N 0.1E


+1
White Meadows
28 November 2023 20:02:33

I have to assume that either you’re being unnecessarily dramatic or you’ve misunderstood the word ‘outlier’?

The Op is only a true outlier for a total of three days across the final seven days of the output, the rest of the time there is some support from the ensemble suite.  It hinges on whether the Op has the behaviour of the jet stream and the associated build of the Scandi high right.

Lack of support does not equal wrong, it just equals huge uncertainty.

Originally Posted by: Gandalf The White 


But yet again… it’s an outlier. 
 
+1
Taylor1740
28 November 2023 20:45:23

I have to assume that either you’re being unnecessarily dramatic or you’ve misunderstood the word ‘outlier’?

The Op is only a true outlier for a total of three days across the final seven days of the output, the rest of the time there is some support from the ensemble suite.  It hinges on whether the Op has the behaviour of the jet stream and the associated build of the Scandi high right.

Lack of support does not equal wrong, it just equals huge uncertainty.

Originally Posted by: Gandalf The White 


it's clearly an outlier on the basis that it doesn't have much support and is therefore very unlikely to evolve in that way or similar. It's way out of the range of the mean which for me is an outlier.
NW Leeds - 150m amsl
+1
Gandalf The White
28 November 2023 20:55:44

it's clearly an outlier on the basis that it doesn't have much support and is therefore very unlikely to evolve in that way or similar. It's way out of the range of the mean which for me is an outlier.

Originally Posted by: Taylor1740 



As you say, it doesn’t have much support; which means it does have some limited support; which means it’s not really an outlier.

Anyway, semantics aside, the point is that it doesn’t make the evolution wrong, it just makes it risky or unlikely.  Since the Op runs at a higher resolution it ought to carry more weight, surely?
Location: South Cambridgeshire
130 metres ASL
52.0N 0.1E


+1
Polar Low
28 November 2023 21:02:15

We can’t really use the mean at that range it gets badly screwed with extreme members.
Some people like means other don’t I’m not a great fan.
Opp could be a trend setter it has made a sold decision at around the 8th which other members can’t see I think it unlikely but it has happened before but we would need to see some momentum.
Gfs always tends to be first when something is up and brewing other than its reluctance to undercut many moons ago hopefully its upgrades have sorted that out.

 
Gandalf The White
28 November 2023 21:23:27

But yet again… it’s an outlier. 
 

Originally Posted by: White Meadows 



If you say so.  But it doesn’t render the Op wrong.  Unless you think otherwise?
Location: South Cambridgeshire
130 metres ASL
52.0N 0.1E


squish
28 November 2023 21:48:40
18z has more of a snow threat fro the SW on Thursday...
D.E.W on Dartmoor. 300m asl
squish
28 November 2023 22:01:07
Its still all very up in the air for anything past 120 in my view.

The low near the Azores on this chart(18z +102) was originally supposed to be moving in from the SW this weekend...

https://modeles16.meteociel.fr/modeles/gfs/runs/2023112818/gfsnh-0-102.png?18 
 
D.E.W on Dartmoor. 300m asl
Downpour
28 November 2023 22:39:04
Some bright, crisp days and frosty mornings in the reliable. Snow likely to be in short supply. Seasonal, though. 
Chingford
London E4
147ft
fairweather
28 November 2023 22:59:31
A lot of people are banding about the term "outlier", some I suspect not fully understanding what a mathematical outlier is and certainly nobody has said which formula they are basing this on. (eg Grubb's, DIxon's) It's not just a case of looking at them and saying one is just because it looks very different to the others. You would be surprised how far out a data point needs to be when the standard deviation is as high as it is at the point in the ensembles we are looking at. Then I'm not sure if the data follows a normal distribution anyway. I imagine that outliers would already have been catered for by the very sophisticated GFS model. I imagine there are better mathematicians than me on here smiling as they read some of this. I think we can broadly say that the operational run is extremely unlikely but that doesn't mean it can be glibly dismissed as an outlier.
S.Essex, 42m ASL
+2
BJBlake
29 November 2023 00:27:15

If you say so.  But it doesn’t render the Op wrong.  Unless you think otherwise?

Originally Posted by: Gandalf The White 



There are 7 out of 22 perturbations On tonight’s output, with some sort of blocked cold spell into FI, with various degrees of blocking and cold, which is 32% - which definitely isn’t an outlier - though not brilliant odds for cold weather fans, but certainly not the common 90% certainty of zonal Atlantic flow we might normally expect at the end of November. I’ll take that - and, as reported,  if climate change is causing a disrupted polar vortex, we might see more such NE flows - but not always of the intensity of cold that we would have expected from this source in decades past. More runs needed for this little candle of hope for festive fare for advent.
Brecklands, South Norfolk 28m ASL
+1
UncleAlbert
29 November 2023 01:10:52
 In the context of the 18z run, the 12z Op is not nearly as much an outlier.  I always think that when cold spells such as the current dig in a little deeper and longer than expected then something may be afoot.  Are these the normal late Autumn shenanigans (to quote Brian) or are we on the cusp of something much different.  So often a pivotal point at this time of year so will it be the form horse or not?
​​​​
+2
nsrobins
29 November 2023 07:12:15
Increasing momentum now for a move to the typical westerly type moving into early December. A decent performance by the GFS suite in particular IMO.
I suspect the odd wayward OP run will still pop up.
 
Neil
Fareham, Hampshire 28m ASL (near estuary)
Stormchaser, Member TORRO
+1
doctormog
29 November 2023 07:17:07
Yet still ECM manages to have me in easterly muck by day 10! 

Looking at the wind rosettes the ensemble data don’t really scream clear westerly to me, rather that it may be just about the favoured option from a range of possibilities (bottom of this image):

https://www.meteociel.fr/cartes_obs/gens_display.php?x=&y=&run=0&lat=57.2&lon=-2.25&runpara=0&type=5&ext=1 UserPostedImage 
Aberdeen
Current conditions (personal WS) 
nsrobins
29 November 2023 07:26:33

Yet still ECM manages to have me in easterly muck by day 10! 

Looking at the wind rosettes the ensemble data don’t really scream clear westerly to me, rather that it may be just about the favoured option from a range of possibilities (bottom of this image):

https://www.meteociel.fr/cartes_obs/gens_display.php?x=&y=&run=0&lat=57.2&lon=-2.25&runpara=0&type=5&ext=1 UserPostedImage 

Originally Posted by: doctormog 



I should say the majority of my analysis is based on the London ENS set for the simple reason of maintaining a consistent metric to predict trends that are representative of the UK as a whole.
On that basis there is only a small number showing an easterly quadrant post 300hrs.
 
Neil
Fareham, Hampshire 28m ASL (near estuary)
Stormchaser, Member TORRO
+1
doctormog
29 November 2023 07:50:59
As easterlies are vile and we have had enough rain here so I can only hope you’re right. My point however was that the signal for the start of December is not strongly westerly: https://www.meteociel.fr/cartes_obs/gens_display.php?x=&y=&run=0&ville=Londres&lat=51.5085&lon=-0.12574&runpara=0&type=5&ext=1 

This is somewhat masked in the ECM day 10 mean but I suspect the EPS would show a range of non-westerly options: https://www.wetterzentrale.de/maps/ECMAVGEU00_240_1.png 
Aberdeen
Current conditions (personal WS) 
DEW
  • DEW
  • Advanced Member
29 November 2023 08:04:04

WX temp chart for week 1 much as yesterday, freezing weather from the east as far as E France, and a touch in Scotland. For week 2, a major retreat as far as a line from E Poland to N Greece - quite remarkable when last night WX was showing the freeze extending all the way to Atlantic coasts. Extra-cold weather still hanging around in NE Russia but much milder for Britain in week 2. Pptn on the Atlantic and across S Europe in week 1, moving E to Atlantic coastal areas in week 2 incl Britain, dying out in S Europe.

GFS Op - LP over Baltic and/or the Alps maintaining a weak N-ly flow over Britain and W Europe to Tue 5th when the Atlantic becomes more active, with a deep 'dartboard' LP 940 mb Wed 6th a couple of hundred miles west of Ireland with S/SW-lies for W Europe, becoming stormy over Britain as the LP centre moves to N Ireland 960mb Sun 10th. The LP fills and moves on E-wards with a standard broad W-ly wind field Wed 13th for everywhere N of the HP up to Shetland 1035mb by then in S France.

ECM - similar to GFS but adds in LP 995 mb S Ireland Mon 4th (this is much further SW in GFS) before offering its version of the LP Wed 6th 970 mb just off SW Ireland. Then somewhat different as the LP reaches Scotland earlier, Fri 8th, and as it moves into the N Sea Sat 10th brings in strong NW-lies.

GEM - closer to GFS in respect of major Atlantic developments than ECM but does include that small feature Mon 4th

GEFS - cold (lowest ca Sat 2nd) with good ens agreement to Wed 6th, then an abrupt return to norm and staying there to Fri 15th with fair agreement for ens members at that stage though a number of runs experiment with colder options. Occasional rain to the 6th in the S, then becoming persistent generally with some big totals in Wales and the SW. 

 
War does not determine who is right, only who is left - Bertrand Russell

Chichester 12m asl
+8

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