Model Output Discussion - The final stretch to Christmas

[Man With Beard]

Looking at the ECM postage stamps still quite a lot of variation in the position of the high at T120hrs, theres only minority support there for the UKMO solution:

 

120.gif

 

Still uncertainty in terms of snowfall, some of those ensembles look more showery for the east and se, others drier for the whole of the UK.

Genoa lows galore on those postage stamps, or at least within a few hundred miles - the classic signature of a cold snap in the UK. Great, great potential therefore for more wintery weather at T120, anything beyond is FI I'd say. And to think a few days ago it seemed this was going to be a two day toppler!

[tinybill]

before  i go on the Santa  run quick look at the models  dare i say it snow for us on DEC 28 !!! roll   on later i can put me feet up and have a drink  or2!!

Edited December 24, 2014 by tinybill

[ReindeerMarmalade]

I rarely post on here (as you can see!) but I'm an avid reader...daily during the summer but obsessively from 1st Nov. I wanted to say merry Christmas and to thank everyone for their insight and dedication in interpreting the models for those of us far less knowledgeable You really are appreciated.

And to anyone unhappy with the outputs now looking more favourable for snow, remember- we probably get your preferred weather type more often in the UK

Merry Christmas, MOD posters. I hope everyone has a great day tomorrow, no matter what the weather does.

[FAB]

This last week has really been fraught with danger in trying to predict what would be happening over the Christmas period and as usual, as an avid back seat fan, I've enjoyed everyone expertise and comments!

 

Merry Christmas one and all. 

[nick sussex]

Genoa lows galore on those postage stamps, or at least within a few hundred miles - the classic signature of a cold snap in the UK. Great, great potential therefore for more wintery weather at T120, anything beyond is FI I'd say. And to think a few days ago it seemed this was going to be a two day toppler!

Yes the Genoa Low is one thing you want to see, the UKMO however I'm not keen on as that moves the main low heights too far east and the high is not favourably orientated. At this point I think its an outlier solution given the other operational runs and the ECM ensembles. We preferably want to see a ne/sw high alignment towards Scandi. However it looks like a dramatic change over mainland Europe with the eternal Autumn/Spring like conditions coming to an end.

 

For those who have got skiing holidays booked in the near future conditions should improve dramatically, I'm sure theres big relief amongst all the ski resorts, at least these can salvage the festive period.

[Nick F]

Genoa lows galore on those postage stamps, or at least within a few hundred miles - the classic signature of a cold snap in the UK. Great, great potential therefore for more wintery weather at T120, anything beyond is FI I'd say. And to think a few days ago it seemed this was going to be a two day toppler!

 

Indeed, quite a turnaround, but not entirely unexpected. 06z GFS ensembles have good support for the block to hold on to at least New Year's Day  Which goes to show that the ensembles guidance can be fickle too, especially when there's a spread of solutions such as has been produced over recent days. But, higher confidence now from the ensemble suite for blocking near the UK through next week rather than a return Altantic mobility.

 

Before the block develops, GFS indicates snow late Boxing Day and overnight into Sat morning across northern England and central/southern Scotland on the northern flank of the low moving SE, more particularly for higher ground looking at forecast dew points and wet bulb temps.The low carries on deepening as it slides SE into the near continent on Saturday, with a strong NEly developing through Saturday - force 8-9 across East Anglia/Kent coastal areas perhaps force 10 southern north Sea. Colder air with lower thicknesses and dew points gets dragged from the NE too, so we could see wintry precip even to lower levels as head into Sunday anywhere from northern/eastern England down towards SE England.

 

In fact 06z GFS shows a small window for snow Saturday night across SE England/E Anglia, as a lobe of vorticity on the northern flank of the low dropping SE into the near continent perks up shower activity here. Looking drier from Sunday as HP builds, with showers confined to eastern coastal fringes, but remaining chilly by day and frosty overnight perhaps right up to New Year. :smiliz34: 

 

Potential that the models may actually be too quick at clearing the weekend low SE over the near continent, so we may hang on to the NEly longer than models suggest., certainly hints from 06z ENS that the low is slower to clear ...

Edited December 24, 2014 by Nick F

[BlueHedgehog074]

Christmas Day, according to the models, does look as though it will be a fairly calm day with cool North-Westerly winds. A scattering of showers towards North-Eastern, Northern and Western areas - one or two of these getting dragged towards the Midlands through the Cheshire Gap. Those to the South and South-West staying quite dry. The 850 hPa temperatures below the 0*C mark for places, so a chance for showers to fall as sleet or snow over high ground to the North, although the -5*C, or cooler, 850mb temperatures towards North-Eastern areas could allow wintriness to the showers in those parts to fall to some reasonably low levels. 

 

It also looks likely that Northern areas will see a frost on Christmas morning with temperature around/close to freezing, but temperatures may struggle to reach any higher than 4*C in the North during the day. Further South, temperatures may get up to 8*C. Despite a few showers around, Christmas Day could make for some nice walking (if it's the type of thing you enjoy), but could feel colder during showers.  :w00t:

 

 

Would also like to wish everyone on here a very Merry Christmas and a Happy New Year. I hope you have a fab one.   :smiliz19:

 

 

 

[Mucka]

3 Key areas of interest in the output for coldies at the moment.

 

The first is of course the exact track and development of the diving low that could give snowfall for some and trigger a longer spell of cold weather.

Too early to put any detail on that at the moment I'm afraid but plenty of fun to be had dissecting snow charts over the coming runs all the same.

 

The second is the positioning and shape of any MLB to our NE after the low passes through. This is very much up for grabs and another area where there could be fairly large changes as far as weather type for the UK from run to run even at such a relatively short time-frame.

The models have only just got to grips with the Scandi high scenario and are currently calculating the possibilities from there.

 

I was going to post about the prospect of shortaves forming in the East flow enhancing the push East of cold air and aiding the longevity and potential of any Scandi high with undercutting into NW Europe but reading through I see Steve M has already posted on this much more eloquently than I ever could.

Even so I think it could be the next big development to look out for if we want a quick and sustained route to cold with a stronger Easterly flow that cuts through the UK rather than Northern Europe.

Things could get very complicated later if this scenario develops as there are also increasing signs of undercut to the West. Huge snowfall potential but also high risk.

 

Even further out we might casually look for signs for retrogression in January and a Greenland high setting up (we are talking deep FI here). This is not currently modelled (but then nor was the Sandi high when several of us were talking up the possibility - it is all about trends)

The anomaly charts will be useless for this as they tend to get outdated very quickly in evolving situations since the ensembles take their time latching onto new possibilities.

rightly people pour scorn on single operational runs being used for forecasting FI (let alone op runs that don't exist yet :smiliz39: ) but in fluid situations where the future pattern is up for grabs they can be useful indicators so look out for future signs of this in FI output (likely post Christmas if it is modelled)

For now there is enough to concentrate on in the shorter term without such idle speculation but I am just sowing the seed for post Christmas - if we get the undercut there could be some very exciting charts appearing post Christmas. (FI output in future model runs)

 

Back to the more reliable and fingers crossed we all see some snow (coldies anyway) at some point in the coming weeks and I look forward to reading the huge array of opinions and the combined knowledge of Netweather members over Christmas. 

 

Merry Christmas all   :smiliz19: (12z's rolling out)

Edited December 24, 2014 by Mucka

[shaky]

Shortwave less deep and further south again and now crosses the midlands at 48 hours :0!!!

[Mark Bayley]

Could be an interesting boxing day snow event for those on higher ground north of the Midlands as the 12z pushes the small low further south. Dewpoints look too high for those on lower ground, but one to keep an eye on (especially with further shifts south)

UKMO further south too

Edited December 24, 2014 by Mark Bayley

[snowy weather]

Shortwave less deep and further south again and now crosses the midlands at 48 hours :0!!!

what does that mean please?

(Im still learning )

[Neilsouth]

Shortwave less deep and further south again and now crosses the midlands at 48 hours :0!!!

 

No charts posted, can you explain if that's good or bad as some of the readers don't know much about shortwaves..

Edited December 24, 2014 by Osbourne One-Nil

[Met4Cast]

Shallower shortwave is better because the warm sector is less.

 

However, because the shortwave is shallower, we see high pressure falling further South-East on this run with less amplification which could have consequences for the longer term as it sends the deeper cold South into Europe rather than advecting it Westwards over the UK

[Neilsouth]

Shallower shortwave is better because the warm sector is less.

 

However, because the shortwave is shallower, we see high pressure falling further South-East on this run with less amplification which could have consequences for the longer term as it sends the deeper cold South into Europe rather than advecting it Westwards over the UK

 

Great! Thanks Daniel, still some time to go though, lots of changes after the big day

[Nick F]

Shortwave less deep and further south again and now crosses the midlands at 48 hours :0!!!

 

what does that mean please?

(Im still learning )

 

I think he means the low moving SE across central parts Friday/Saturday. It's one of those grumbles John Holmes and I have, as we tend to use 'shortwave' to refer to a shortwave upper trough rather than the actual surface low refered to.

 

Not sure how the use of the shortwave word instead of low pressure has crept into popular nomenclature on here, but as its Christmas, I let everyone off :smiliz19:

Edited December 24, 2014 by Nick F

[Met4Cast]

GFS(P) keeps the shortwave a deeper feature, so even at this very short timeframe we still haven't got model agreement! 

 

The GFS(P) does bring a widespread snow event

 

 

I can't wait for the Parallel to go live, having two different GFS models is annoying and probably doesn't help with working out thats going to happen

[snowy weather]

I think he means the low moving SE across central parts Friday/Saturday. It's one of those grumbles John Holmes and I have, as we tend to use 'shortwave' to refer to a shortwave upper trough rather than the actual surface low refered to.

Thanks, and is it good or bad for cold and snow in SE?

[Barry12]

UKMO looks cold on Sunday

 

 

:smiliz19:

[Bartlett High]

Things looking good for early jan perhaps?

[igloo]

this afternoons GFS is doing its best to flatten the pattern fairly quickly and leave us in the dreaded bartlett is it no progressive as usual it would not be the first time

 

Edited December 24, 2014 by igloo

[Barry12]

Things looking good for early jan perhaps?

 

Yeah, a Bartlett high looks very unlikely.

[mulzy]

this afternoons GFS is doing its best to flatten the pattern fairly quickly and leave us in the dreaded bartlett is it no progressive as usual it would not be the first time

 

 

Not a Bartlett mate....

 

However the pattern on both the GFS and GFSP seems to have shifted a little south.

Edited December 24, 2014 by mulzy

[shaky]

If you think the gfs has that low too far south then take a look at the ukmo 60 hour chart!! Has the low on the south coast!! Snow event across midlands in that case!!

[Mucka]

UKMO making less of the warm sector on Saturday as the shortwave passes through. That would enhance snow chances further West and to lower levels in the North.

 

[Met4Cast]

UKMO, GFS and GFS(P) All in fairly good agreement with the tracking at least, intensity varies between the models.

 

Snow risk across Northern areas in particular seems to be increasing, even to lower levels too. The Midlands South perhaps some back edge snowfall? Hard to say, really need to wait until it comes within range of the high res models before looking at that kind of detail.

 

GFS(P) doesn't seem to be flattening the pattern quite as fast as it's GFS counterpart. The GFS hasn't exactly covered itself in glory these last few days though.

 

EDIT: UKMO and GFS(P) similar with the amplification. GFS flatterns faster than both

Edited December 24, 2014 by Daniel Smith