Model Output Discussion - Christmas and New Year

[stodge]

Evening all

With Storm Bella showing her hand across Ireland and western Britain, the immediate wea6ther concerns for rain and strong winds will take precedence. The active debate over possible wintry precipitation will no doubt be continuing but I'll take my usual nightly look at the medium to longer term trends and leave the short-term and nowcasting to others.

Very strong output for cold weather fans yesterday with a prolonged cold spell likely though never as cold or as snowy as some would like (or hope or expect). The 850s were, in the initial stages, not seemingly supportive of the excellent synoptics but with time the air gets colder and that's the direction of travel for which snow fans will be looking tonight.

12Z GEM: T+120 takes us to New Year's Eve and a slack N'ly covers the British Isles with the remnants of Bella over Scandinavia as a weak but general trough and heights extending from Greenland south and south-east into the Atlantic with the next trough barely off the Canadian coast. Uppers zero to -4 with -8 850s just to the north of Scotland. By T+180 little has changed - the trough lies to the north east and east ut extends through the British isles to north-west Europe so we keep a slack N'ly flow. The Atlantic HP is ridging NE toward new heights emerging out of NW Russia. An LP is off the Azores. Uppers have cooled further to -4 to -8 generally. From T+180, the northern part of the trough phases with a new LP forming off the SE Greenland coast but that flow is cut off by heights building through Iceland. However, the infusion of energy causes the LP to re-strengthen as it moves south while heights build to the north and east. The British Isles remains under a cold airmass.

12Z GFS - you'd have to say GEM looks very good for fans of snow especially into FI. I'd be astonished if GFS OP was better at the same timescale. No great surprises at T+120 with the N'ly flow in place and shortwaves within the general circulation of the trough. The coldest air staying to the west of the British Isles at this time. Well, a very different evolution beyond there to T+180 as the Atlantic heights collapse back south and a new trough develops over or to the west of Iceland with a milder airflow heading toward the north of the British Isles. The remnants of the trough are over Europe but the airmass remains cold at this time though I don't like where this evolution is going. Need I have worried? It seems not - there's more than an element of rinse-and-repeat as the LP sinks south across the British Isles but, unlike Bella, this goes cleanly through and heights rise behind to the north and north-west drawing in an NE'ly flow by T+240. Cold air over the British Isles but a steep temperature gradient (which snow fans will like) and some much milder air on the eastern side of the LP pushing up into Denmark. By T+312 the weather is settling as HP edges in very slowly from the west. The trough is now over Scandinavia ad milder air is trying to edge in.  By T+384, a more normal pattern is re-establishing though HP dominates over southern Britain.

12Z ECM - it's not worth stressing over the return of a milder weather more than a fortnight away. The divergence with GEM begins at T+180 and that's more of an issue. Let's see what ECM has to offer. T+120 is no real surprise - obvious similarities to GEM but weaker heights over Greenland more akin to GFS OP but we'll see. The evolution is again different to the other models - by T+192 the Atlantic HP has ridged NE through northern British to heights building over Scandinavia while the LP is in the classic "Gulf of Genoa" position leaving a slack NE'ly over much of southern Britain. Uppers of -4 to -8 widely by this time. By T+240 the HP is centred off the Hebrides and a NE'ly covers most of southern Britain with calm conditions elsewhere. Plenty of cold air in evidence and a cold feed on which to draw but the onus perhaps more on frost by this time.

12Z GFS Parallel - ECM decent for cold but perhaps less so for snow in FI. On then to my new mate, the GFS Parallel and by T+120 no great surprises. The T+180 evolution is quite messy with the new Atlantic trough extending SE well to the west of the British isles forcing the HP north to Iceland while the residual trough remains over southern Britain. Cold air remains over the British Isles at this time. The evolution continues messy to T+240 but clear signs of the Atlantic pattern re-establishing and moving toward the British Isles which remains in a slack cold flow. From there we see a pattern we sometimes see - without a strong PV to fire up the jet and drive the systems east, the Atlantic LP goes nowhere and that enables downstream heights over Scandinavia and by T+312 we have a strong HP over central and northern Scandinavia and the British Isles in the middle between the colder and milder airmasses.  BY the end of FI, neither the cold not the mild "wins" - the stalemate allows new heights to develop over the British Isles and the run ends anticyclonic. However, the colder airmass is in charge with the milder air held to the west.

Looking elsewhere, 12Z Control ultimately ends mild but messy. The trend is toward some form of anticyclonic evolution as we head toward mid-January but the placement and orientation of said HP varies as you would expect at this stage. I gave to say very different evolutions on the 10HPA profile this evening - Parallel goes for a split, OP has the strat weakened and coming under renewed pressure in the second week of January while Control keeps the strat much stronger.

Conclusion - slight changes but nothing substantial this evening. An extended colder period looks on the cards - the interesting sign from GFS this evening is the evolution toward an anticyclonic solution which can be very cold if set up in the right place (Scandinavia). This is witness to the weakness of the PV and the absence of a strong zonal jet which gives more scope for amplification. Plenty of weather to comment on in the coming days but let's hope everyone stays safe from the initial assault of Bella overnight.

 

[Tim Bland]

Do we see a mean output of DP temps for EC? As above alluded to by Blue they are on the high side but as others rightly say an easterly is usually dry air with low DP?

[Duane S.]

Knowing the background signals as we do, this is a superb chart

Bitingly cold at the time and likely to be coming out of the ‘wane’ phase. Next step I'd assume would be a renewed amplification wave and maybe for us look NE for something more extreme? 

But of course this is just one outcome of many, of which seemingly the great majority point towards cold, cold and continued cold!
 

Also, 58 years ago today,  we had this...

It was the precursor to one of the most memorable winters in living memory of course. No comparisons meant in terms of synoptics but worth remembering the other truly great uk winter of the past 75 years looked like this on Boxing Day, and was still a good few weeks away from getting going yet!

Basically. Have patience!!

 

[Bartlett High]

6 minutes ago, s4lancia said:

Knowing the background signals as we do, this is a superb chart

Bitingly cold at the time and likely to be coming out of the ‘wane’ phase. Next step I'd assume would be a renewed amplification wave and maybe for us look NE for something more extreme? 

But of course this is just one outcome of many, of which seemingly the great majority point towards cold, cold and continued cold!
 

Also, 58 years ago today,  we had this...

It was the precursor to one of the most memorable winters in living memory of course. No comparisons meant in terms of synoptics but worth remembering the other truly great uk winter of the past 75 years looked like this on Boxing Day, and was still a good few weeks away from getting going yet!

Basically. Have patience!!

 

More posts like this please!

[ANYWEATHER]

4 minutes ago, Scott Ingham said:

But snow cant be modelled until within 48 hours as the latest shift north in snow on the higher res models show.

To say no snow based on modeos 144+ is futile 

If its cold enough snow will always pop up in the way of troughs etc.

Synoptics show a possibility of cold all the way through January intensifying week on week.

Snow comes hand in hand

December 2010 looked dry in fact it showed 8 days with no snow on the snow rows 120 hours + so historic us very much a possibility 

A good post. December 2010 and the like computer models did not pick up on any snow what fell until the last minute.  Mondays  snow will be impossible too forecast , the trend is there but snow surprises are on the way for all...Great News for Snow Lovers but......Just watch this ...........................................Space!

[Man With Beard]

49 minutes ago, Weathizard said:

Beautiful ECM mean, Atlantic absolutely dead and buried without the SSW and other factors about to come into play 

Fantastic means. In the past, mean easterlies on the ECM have tended to verify (at least, you never see an easterly unless it's on the mean chart first!). However, after jumping at a mean Greenland High the other night, I think I will sit on the fence for a couple of runs to see how the pattern unfolds!

[Kent Clipper]

The 12Z EC Ens for Reading are trending ever colder. The median T2max now struggling around 2 to 3c on most days with sub zero minima on many nights. We are in an unusual an exciting position. This is a slow and steady burner. The old weather lore saying 'short notice, soon pass. Long notice, long pass' feels very apt at present. 

ECMWF Forecasts

WWW.ECMWF.INT

The 15 day wind vector plots are even more tantalising with a defintive and favoured N or NE flow @ days 7-13. 

ECMWF Forecasts

WWW.ECMWF.INT

 

Edited December 26, 2020 by Kent Clipper

[bluearmy]

This really isn’t a 2010 scenario  ....... comparisons are surely going to mislead members into high expectations which are unlikely to be met for the majority. 

[ICE COLD]

23 minutes ago, Allseasons-si said:

That is a cracking mean at day ten with cold continental dry air from the east,it would certainly feel bitter.

eps and ext eps at day ten and we are still on course for a cold spell guys.

and check this out,nearly all members going for a reversal in the strat.

sos for short text,late eating my tea this evening.

 

 

 

You must of really wanted to eat your tea mate that EC zonal wind charts is one from the 14th December, I would of though the updated one is a lot better

Edited December 26, 2020 by ICE COLD

[Scott Ingham]

10 minutes ago, ANYWEATHER said:

A good post. December 2010 and the like computer models did not pick up on any snow what fell until the last minute.  Mondays  snow will be impossible too forecast , the trend is there but snow surprises are on the way for all...Great News for Snow Lovers but......Just watch this ...........................................Space!

Its the same EVERY time we have a cold spell.

Oh it looks great but no snow is forecast.

Because people dont realise you cant forecast any snow until within 48 hours out.

For any newbies stick to using something like Euro4 and see if anything has been picked up on 

Met warnings can and do pop up at any time at short notice in these spells

[sheikhy]

Deeper low on icon at 36 hours!!not sure if it makes a difference on where the snowfall hits this time

[MattStoke]

Big upgrade on precipitation for Monday from the ICON.

[Eskimo]

See my point again

ICON 18z


Same time 12z. Differences are ridiculous run-to-run. Icon showing a band of snow/sleet across central areas.

Edited December 26, 2020 by Eskimo

[sitrap]

This reminds me of December 1978 - we had a mildish December, and around mid-late December there were widespread floods, then at the end of the month a big storm swept down the country, and we woke up in the New year with about a foot of lying snow, and a strong east wind which seemed to hang around for weeks. I was living in Kent at that time, and I had only recently erected a weather station in the garden, and been taking readings since August. I was so excited to be witnessing the first big snow event since 1962-63 (when I was less than a year old). Really hoping for for a repeat this year - I really feel something's coming......

[stodge]

7 minutes ago, bluearmy said:

This really isn’t a 2010 scenario  ....... comparisons are surely going to mislead members into high expectations which are unlikely to be met for the majority. 

No, and the other thing is nobody remembers January or February 2011.

We "could" be looking at a protracted period of colder conditions (7-14 days) with occasional bursts of severity but the real prize would be repeats of that into January and February. I wonder if it will be more like the winter months of the mid 1980s with prolonged periods of cold conditions and the threat of snow and the absence of mild zonality but without record-breaking numbers or snow depths.

[Kasim Awan]

5 minutes ago, sheikhy said:

Deeper low on icon at 36 hours!!not sure if it makes a difference on where the snowfall hits this time

Yes, the snow is further inland. Almost a full hi res agreement for a central England track. Cumbria to Cheshire to Leicester to the Chilterns at risk atm. 2-5cm in a concentrated area within this region which is not yet resolved; probably wont be until nowcast times. 1-3cm widely early before marginality kicks in. With a pivot 10cm somewhere locally. Lots of marginality enducing factors in operation away from the main precip core east coast south of m4 etc.

 

Edited December 26, 2020 by Kasim Awan

[Ols500]

Just now, Eskimo said:

See my point again

ICON 18z


Same time 12z. Differences are ridiculous run-to-run. 

 

Theres no point lol its nowcast every time, even BFTE the showers couldn't be pin pointed it was a now cast, always has, always will be.

[sheikhy]

3 minutes ago, Kasim Awan said:

Yes, the snow is further inland. Almost a full hi res agreement for a central England track. Cumbria to Cheshire to Leicester to the Chilterns at risk atm. 2-5cm in a concentrated area within this region which is not yet resolved; probably wont be until nowcast times. 1-3cm widely early before marginality kicks in. With a pivot 10cm somewhere locally. Lots of marginality enducing factors in operation away from the main precip core east coast south of m4 etc.

 

Leicester looks like getting quite a hit from that and icon has now moved to euro4!!

[Kasim Awan]

2 minutes ago, Ols500 said:

Theres no point lol its nowcast every time, even BFTE the showers couldn't be pin pointed it was a now cast, always has, always will be.

This a front so it is much different. Confidence is high now. Hope the Met don't lag with this one.

[Scott Ingham]

8 minutes ago, bluearmy said:

This really isn’t a 2010 scenario  ....... comparisons are surely going to mislead members into high expectations which are unlikely to be met for the majority. 

Just to re-affirm for anyone new if you mean by my previous post. 

No comparison is made to 2010 in regards to the cutrent set up as they are miles apart but the over riding message is snowy surprises can and do show up at 48 hour notice periods and anything longer range showing a cold predominantly dry period should be taken with a large pinch of salt until were in that 48 hour time frame.

I do however believe we have a ticket to the raffle for longevity of below average temperatures in comparison. Just not the severity of these temperatures compared to this period as currently stands based on current output. 

Chances are still low for very sever cold to deveolp due to the timeframe and lack of an idea how the ssw forecasts manifests. I.e split or reversal and what this means to the longwave pattern that manifests from this

[Eagle Eye]

Primordial Soup for snow. 

 

[Allseasons-Si]

14 minutes ago, ICE COLD said:

You must of really wanted to eat your tea mate that EC zonal wind charts is one from the 14th December, I would of though the updated one is a lot better

Yep sorry,i did download the latest but it came up with that,strange

here it is from the 24th.

[ICE COLD]

1 minute ago, Allseasons-si said:

Yep sorry,i did download the latest but it came up with that,strange

here it is from the 24th.

No need for a sorry mate no worries. That looks brilliant.

[markw2680]

5 minutes ago, Kasim Awan said:

Based on latest hi res model output.

I’d actually be quite surprised if it went that far north east come the time of it but you never know

[booferking]

1 minute ago, Kasim Awan said:

Based on latest hi res model output.

What we talking about here Brexit or Midlands south east thread.