Model output discussion - The run up to Christmas

[Griff]

14 minutes ago, Tim Bland said:

Morning gang. Loving the ECM this morning. Position is obvious subject to massive change but that low / PV ruminants drops 20cm of snow on its way down ️

Just for fun I've had a look at my "windy" app for this week's weather that runs until the 25th comparing forecasts from different models. A couple show some nice surprises IMBY on Christmas eve... 

[mountain shadow]

37 minutes ago, BLAST FROM THE PAST said:

It’s raining outside now and the rain feels cold.  So it’s likely to be ‘very cold rain’ or snow?

BFTP

Imagine if it were something worse!

The dreaded sleet.

[Eagle Eye]

Sensational Toppler on the GFS control run. 

Merry Xmas

[Tim Bland]

Most GEFS are a tad colder around 27th allowing for more in the way of snow. 70% around Birmingham !

[Anthony Burden]

Lots going in the atmosphere and ground level,looking very wintery especially after Christmas 

snow undoubtedly on the agenda for most of U.K.Time to dig out the sledge and ice skates.

[bluearmy]

6 minutes ago, Hotspur62 said:

Just a quick one from me.Although I have reasonable knowledge it is nothing like most on here so hence the hypothetical question-To me if that was a 9 day chart it would seem the high in the Atlantic would topple over to the UK as angle looks that way?Is it the high to the East that is stronger that keeps firmly in place or am I totally wrong in that assumption?thanks in advance to anyone.

Looks like The Russian ridge holds the sceuro trough in place. The trend for that ridge to strengthen remains this morning on the eps .....as mused last evening, whilst the Atlantic ridge continues to ebb and flow, we see systems dropping in on a mainly nw/se axis into the trough.  How that manifests itself dictates whether wet or white .... 

and do we then see the Atlantic ridge extend across to its Russian cousin ?  I always look for a cold pool somewhere in Russia at times like this when there is a chance we could see a Siberian ridge push west with med low heights likely ....should be nothing more than a note in the back of your mind but there is one at day 10 on the ec op. It likely won’t be there in twelve hours but it might come back .....

[Nick F]

Synoptically looking great on the 00z runs this morning, the T850s don't look much for a screaming northerly next week, however, those worried by the poor looking T850s, the air thicknesses and surface dew points modelled don't look quite so bad for snow, but this far out are subject to change. 

I prefer to use the thickness and dew points to look for the potential for snow, I know it's futile this far off, but  850-1000 hPa thickness of 1290-1300 gpdm and 500-1000 hPa thickness below 524 gpdm and a dew point around 0C the upper limit for snow to fall, just about meet that across many parts Tuesday onwards next week as the flow turns northerly on GFS op. 

Longer term, looking at the extended  00z EPS 500 hPa mean, a signal for the trop vortex over Canadian arctic to retrograde toward Alaskan arctic - this may open up the possibility for high latitude blocking while maintaining low heights over mainland Europe as we head into the New Year. So looking good.

With this background state of blocking and the GFS still signalling for a major weakening of the SPV and perhaps SSW in January, it's looking very interesting for coldies for the rest of winter, should everything fall in place ...

Edited December 21, 2020 by Nick F

[Vikos]

Good morning to my british friends

<--- white numbers are the height of the 0°C Isotherm in meters

a somewhat more realistic (not to be equated with pessimistic) view of certain things apart from the cold hype in this forum means something like an exclusion or an ingnoration, but ok, then let's be a grinch. but the external circumstances do not let me dream of winter wonder to the lowlands in the near future until new year's eve, to put it quite dryly. Too much mixing of the air mass with a high 0 ° C limit, high moisture% pushing dew points up, inflow over the warm north sea

Yet again, it's still to early to discuss excact outcomes after 144, but I would rather remain skeptical due to the experiences of the last few years. I just don't see the enough power in the system (really cold air masses).

Future will show.

So, with no anger, it's "just the weather", and ATM there are things in the world which are much more important than if it will snow here or there or not. As europeans, we need to stick together, somehow

Edited December 21, 2020 by Vikos

[Man With Beard]

General pattern continues to look good for a general coldish spell after Christmas. I'm anticipating the next issue, which is either a good thing or bad thing depending what side you fall upon, may be identifying dreaded mild sectors as secondary frontal areas move into the cold flow from the north west. Fantastic snow makers if you are in the eastern flank, but rain makers just a few miles to the west. It's never easy chasing snow...

[sheikhy]

3 minutes ago, Man With Beard said:

General pattern continues to look good for a general coldish spell after Christmas. I'm anticipating the next issue, which is either a good thing or bad thing depending what side you fall upon, may be identifying dreaded mild sectors as secondary frontal areas move into the cold flow from the north west. Fantastic snow makers if you are in the eastern flank, but rain makers just a few miles to the west. It's never easy chasing snow...

To even be in a position to talk about snow right is absolutely fantastic!!!chalk and cheese compared to last year!!!

[Anthony Burden]

9 minutes ago, Nick F said:

Synoptically looking great on the 00z runs this morning, the T850s don't look much for a screaming northerly next week, however, those worried by the poor looking T850s, the air thicknesses and surface dew points modelled don't look quite so bad for snow, but this far out are subject to change. 

I prefer to use the thickness and dew points to look for the potential for snow, I know it's futile this far off, but  850-1000 hPa thickness of 1290-1300 gpdm and 500-1000 hPa thickness below 524 gpdm and a dew point around 0C the upper limit for snow to fall, just about meet that across many parts Tuesday onwards next week as the flow turns northerly on GFS op. 

Longer term, looking at the extended  00z EPS 500 hPa mean, a signal for the trop vortex over Canadian arctic to retrograde toward Alaskan arctic - this may open up the possibility for high latitude blocking while maintaining low heights over mainland Europe as we head into the New Year. So looking good.

With this background state of blocking and the GFS still signalling for a major weakening of the SPV and perhaps SSW in January, it's looking very interesting for coldies for the rest of winter, should everything fall in place ...

Hi Nick thanks for that very informative weather summary,can I ask your opinion of this low pressure 

system forecast for this Wednesday/Thursday.Do you feel on its northern edge as it pulls away east/ southeast

from the south of U.K. a possibility of some rain turning to snow.

[IDO]

18 minutes ago, Hotspur62 said:

Just a quick one from me.Although I have reasonable knowledge it is nothing like most on here so hence the hypothetical question-To me if that was a 9 day chart it would seem the high in the Atlantic would topple over to the UK as angle looks that way?Is it the high to the East that is stronger that keeps firmly in place or am I totally wrong in that assumption?thanks in advance to anyone.

For me, this is not a typical NH profile. We have a broken tPV with the main vortex on the Asia/Pacific side and a daughter vortex to the NW. So the power game of high -v- low (tPV) seemingly now favours the Atlantic high. Any pattern corrections in a stagnant NH appear to come form an injection of heights from the west and it is that interaction that may move the pieces more than the usual suspects post d9...

d10 mean> d16 op> 

...that morphs into an omega block by d16 (op).

Getting the ScEuro trough in place was always likely to be our best solution for some cold from this trop led upcoming pattern (with that pesky Russian block). Certainly the opportunity for cold in Europe from this spell is limited and for once the UK may benefit more than most. The usual caveat that the models are right!

[Methuselah]

1 hour ago, Tim Bland said:

Morning gang. Loving the ECM this morning. Position is obvious subject to massive change but that low / PV ruminants drops 20cm of snow on its way down ️

Those'd be Santa's reindeer, I'd guess? But we are, I think, headed for something special... And, by the time this is all over, I might even know what a Greenland High is!

[Nick F]

23 minutes ago, Anthony Burden said:

Hi Nick thanks for that very informative weather summary,can I ask your opinion of this low pressure 

system forecast for this Wednesday/Thursday.Do you feel on its northern edge as it pulls away east/ southeast

from the south of U.K. a possibility of some rain turning to snow.

I would consider it a rather low possibility at the moment, none of this morning's models suggest snow across the south on the northern edge of the rain shield as it pulls away. Perhaps maybe over the Welsh mountains. Cold/dry enough air from the north not  catching up this rain unfortunately to allow it fall as snow.

A few wintry showers down eastern coastal areas on Xmas Day though, that 12/1 bet for Norwich White Xmas from William Hill perhaps would've been a good punt.

Edited December 21, 2020 by Nick F

[carinthian]

2 hours ago, carinthian said:

Morning all. Good agreement between UKMO and GFS at 144t. Maybe UKMO speeding up the advance of the cold front on Boxing Day. Chance of snowfall in parts of SE Britain now increases to 30% based on the formula I mentioned yesterday from 29th December. Looks like the low will become elongated just to the east of the British Isles as we head towards the New Year with its centre close to the Low countries. Not a bad place to produce a prolonged colder spell.

Should get an up-date in an hour or so from the portal team over here.

C

 

The snow model used for us over here starts producing outer perimeter results from 10 days . Obviously, the percentage predictive results increase with the shortening of time. Its only with-in 48 hours of a snow event that the fine mesh models starts predicting more accurate location and amounts. So the question I ask the team, whats the snow prospects for the UK ? Based on their model  the prospect of snow starts becoming more interesting widely from 29th December with a % rate today of 30% for that to happen by day 8. They report that the % rate as a guide line increases by 10 % per day ( based on a continuation in the predictive theme of the models ) , hopefully , no big switch to take place . 528 dam markers or below are being shown over the British Isles during the last few days of the year, so that would indicate a greater potential for snow. Meanwhile over here  in resort the first results from the snow model indicate 20cm of fresh snowfall over Christmas Eve into Christmas Day.  Hope that helps.

C

[sheikhy]

Icon heading straight into greenland at 120 hours and upgrade on the 00z for the same timeframe!!

[chris55]

GFS picking up on this little feature this morning (just south of Iceland on this chart.)  This aids in dragging down some slightly colder 850s into the flow.

 

 

Shortwaves/features/troughs will be popping up left right and centre within the flow I would imagine through next week. Snow could literally fall anywhere at short notice if the air is cold enough. 
 

Ive ordered three sledges! At the very least I’m expecting some hill snow over the Cotswolds at some point next week  

 

[Mair Snaw]

So here we are another morning comes around and the models are better again, ticking down nicely into a time frame where we start to think this could really happen.. just keep getting flashbacks to December 2012 and that ECM period.. inside t96 and it all just vanished in one set of runs.. surely 2020 cant be that cruel after everything else thats happened so far. 

[johnholmes]

Monday 21st and 500 mb anomalies

Ec-gfs and again both strong +ve heights and contour ridging, Greenland area and Russia Scandinavia and Russia again over pole? Deep troughing e of Greenland ridge centred almost over uk n-s

Noaa has got more meridional looking again after its chart on Sunday but very modest looking but with v large +ve anomaly.

Upshot is that overall the meridional pattern is probably going to feature most days through the next 2 weeks as the 8-14 is possibly a touch more meridional that 6-10 and upstream pattern also looks conducive to it continuing.

As to the surface weather the only comment valid looking 500 mb or 18000 ft above is that the contours, from the areas of origin are ‘modest’, around 540 DM in the Borders area, back over the northern end of the Gt Lakes and just south of Alaska, so not in the very cold category for sure. That does not mean that any individual surface feature may not entrain, temporarily, colder air. Anyway the synoptic models are the ones to use for ppn etc. Do remember though beyond 144h compare like with like for the overall pressure pattern and it is a waste of time at those ranges regarding ppn type!

ECMWF/GFS DAY 8-10 MEAN 500MB HEIGHT COMPARISON

MP1.MET.PSU.EDU

Climate Prediction Center - 6-10 Day 500mb Outlook

WWW.CPC.NCEP.NOAA.GOV

 

Edited December 21, 2020 by johnholmes
spelling

[winterof79]

Surely that's not three bad

[Weathizard]

6 minutes ago, sheikhy said:

Icon heading straight into greenland at 120 hours and upgrade on the 00z for the same timeframe!!

Indeed. The angle is much better than the 0z, reminds me of one of the early GFS runs yesterday with the way it’s opening up heights between GL and the arctic high.

[ITSY]

More excellent runs the morning. My only concern, mentioned by others, is how Far East the pattern goes and whether we wind up stuck under the high ourselves. I doubt it as it’s been fed by waves off the American coast by that’s clearly what the Meto have thought for some time reading their longer term outlooks. I would like to see that changed soon. One of those rare occasions where the cross model consensus is so overwhelming I think it will but just a nerve I have!

[Radiating Dendrite]

3 minutes ago, ITSY said:

More excellent runs the morning. My only concern, mentioned by others, is how Far East the pattern goes and whether we wind up stuck under the high ourselves. I doubt it as it’s been fed by waves off the American coast by that’s clearly what the Meto have thought for some time reading their longer term outlooks. I would like to see that changed soon. One of those rare occasions where the cross model consensus is so overwhelming I think it will but just a nerve I have!

Hopefully the Russian high will stop this eastern progress though?

[tight isobar]

Rapid transition alerts @rain to snow.. via 6z!!!

Edited December 21, 2020 by tight isobar

[goosey007]

8 minutes ago, Mair Snaw said:

So here we are another morning comes around and the models are better again, ticking down nicely into a time frame where we start to think this could really happen.. just keep getting flashbacks to December 2012 and that ECM period.. inside t96 and it all just vanished in one set of runs.. surely 2020 cant be that cruel after everything else thats happened so far. 

Easterlys always a more fragile setup leading up to it.....more confident with current set of synoptics and more so consistency especially from the GFS over the last 3 days or so.....winter is comming ❄