General Model Output Discussion Tuesday December 22Nd:

[Thundery wintry showers]

I think Frosty039 is slightly underdoing the chances of snow- I don't see Scotland or upland parts of northern England having a remote chance of a wintry mix until Boxing Day. The Midlands and lowland parts of northern England will be marginal with some places seeing accumulations of snow and others seeing more of a wintry mix, the latter more likely the further south you go. Southern England will probably see rain or sleet from this system except for high ground.

[stewfox]

It's not an assumption, it's how the met office see it and I happen to agree with them, it will become less cold in southern england and probably further north as well, face reality.

We shall see , although I think T72 is beginning to become into reliable time frame, pub run should 'half nail' what happens to the colder air as it tracks back south on late xmas eve. Although T84+ there is still a lot of disagreement

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For Christmas eve, as a band of rain, sleet and snow will be moving northwest through the day, generally falling as rain and sleet in the south but becoming snowier further north. As it clears through to the east though, it will pull the colder air back south perhaps allowing the tail end of it and certainly any showers following in behind to fall as sleet and snow - even in the south. With that due to clear through overnight on Xmas eve it could mean waking up to a little bit of the white stuff on Christmas day even in those places which haven't got residual lying snow from previous falls

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[nick sussex]

A good gfs run so far, it doesn't phase the two lows together and if this verifies then it could be a very interesting run up to the New Year. If the Atlantic low can disrupt sending shortwaves east into France then a cold reload is likely. The north at the moment looks likely to remain cold throughout.

Edited December 22, 2009 by nick sussex

[Thundery wintry showers]

I agree with the Met Office's assessment and it is certainly looking good for a white Christmas in north-east England at the moment (even the east coast is pushing towards the right side of marginal)- with the Midlands and north-west being in with a chance as well. For Scotland a white Christmas in the snow cover sense is looking a certainty in areas that are currently snow-covered with the possible exception of the west coast.

I do not expect much in the way of wintriness to make it to lowland parts of southern England but I think upland parts could, as the Met Office suggests, see a sprinkling of snow on Christmas morning.

[Barb]

Looking interesting for major snow event 28th/29th, models have been hinting at this for a few days now.

~Foot of snow in places

Edited December 22, 2009 by Barb

[nick sussex]

I'm surprised at the lack of posts in this thread given the synoptics. Are net weather members getting bored of the cold and snow! this is close to a major snow event, but as i mentioned earlier its crucial the low to the sw and the one near the uk don't phase together in the earlier timeframe, in the euros they phase these meaning its a longer road back to cold.

Edited December 22, 2009 by nick sussex

[johnholmes]

In a way its fortunate Nick as some of the one liners are busy filling up the regional threads-tread in there only if you have to !

As you say its a fascinating time as I've tried to explain in my blog-its also very difficult to try and make an unbiased post when its cold and snow (in reasonable measures) that are the most interesting at this time of year.

[Cal]

A bit far out but

El Classico setting up? If it comes of someone's going to get a serious amount of SNOW

http://91.121.94.83/modeles/gfs/run/gfsnh-0-168.png?12

[Nick L]

I'm surprised at the lack of posts in this thread given the synoptics. Are net weather members getting bored of the cold and snow! this is close to a major snow event, but as i mentioned earlier its crucial the low to the sw and the one near the uk don't phase together in the earlier timeframe, in the euros they phase these meaning its a longer road back to cold.

Perhaps it's because we are in the middle of a cold spell!!

[snowingtequila]

Potential for flooding on Wednesday night? Could be a lot of rain in the south, combined with snow melt it could be a nasty combination:

http://212.100.247.145/viewimage.pbx?type=gfs;date=20091222;time=12;ext=33;file=ukprec;sess=8f187d40dbdaf99165ba2eb5f95c9595;

Will certainly be rain, uppers of -2, positive dew points and temperatures.

never so sure it is a good idea to say certainly where snow is concerned, a degree here or there, slight change in dew point significant snow cover on the ground could result in very different weather.

[snowmadchrisuk]

UKMO keeps the -5 Uppers across most of the country Wednesday night , apart from the South coast. GFS has them higher so who will be right ? The UKMO has doner ather well this week .

[nick sussex]

In a way its fortunate Nick as some of the one liners are busy filling up the regional threads-tread in there only if you have to !

As you say its a fascinating time as I've tried to explain in my blog-its also very difficult to try and make an unbiased post when its cold and snow (in reasonable measures) that are the most interesting at this time of year.

Hi John

I'm close to passing out here with excitement especially as the ukmo is a big upgrade to the 00hrs run! which is strange as now being in sw France alot of these possible snow chances won't effect me until perhaps much later on. These are synoptics not seen for years in the UK. I'm just trying to put myself back in Sussex and this evenings output so far from the gfs and ukmo is close to sensational!

[Nights King]

UKMO keeps the -5 Uppers across most of the country Wednesday night , apart from the South coast. GFS has them higher so who will be right ? The UKMO has doner ather well this week .

-5 uppers would surely give us on high ground a shot at a decent snow event wed night? Could be another knife edge situation though.

[Barb]

I'm surprised at the lack of posts in this thread given the synoptics. Are net weather members getting bored of the cold and snow! this is close to a major snow event, but as i mentioned earlier its crucial the low to the sw and the one near the uk don't phase together in the earlier timeframe, in the euros they phase these meaning its a longer road back to cold.

Normally I'd dismiss charts that far out but it's been showing for a few days now and many runs and it's getting into a semi-reliable timeframe. It would be a very very special event for the right places.

[kold weather]

Very interesting run, this run shows a similar little low running just south of the UK between 168-192hrs like the 0z ECM had, would be a monster snowfall in the south if that run were to come off:

http://www.wetterzen...s/Rtavn1801.png

Still thats a very long way off yet...FI looks decent enough as well though not quite as cold as this cold spell...eventually the AO turns more +ve AO at the end of the run though the PV remains split...so quite possible that any milder spell would be only short-lived if this run came off.

Edited December 22, 2009 by kold weather

[cooling climate]

Hi John

I'm close to passing out here with excitement especially as the ukmo is a big upgrade to the 00hrs run! which is strange as now being in sw France alot of these possible snow chances won't effect me until perhaps much later on. These are synoptics not seen for years in the UK. I'm just trying to put myself back in Sussex and this evenings output so far from the gfs and ukmo is close to sensational!

Yes UKMO at t144 looks to be going for the undercut which would be a snow heaven for the UK and then onwards to

the 06z GFS evolution there after and yeah I would take that.

Excellent synoptics again.

[johnholmes]

Hi John

I'm close to passing out here with excitement especially as the ukmo is a big upgrade to the 00hrs run! which is strange as now being in sw France alot of these possible snow chances won't effect me until perhaps much later on. These are synoptics not seen for years in the UK. I'm just trying to put myself back in Sussex and this evenings output so far from the gfs and ukmo is close to sensational!

without going into manyana territory and staying within the SUPPOSEDLY reliable time frame of 3-5 days then the models, all 3, have backed away from the mild idea of several days ago, not totally, in a series of jolts one might say. Now there is even doubt looking at some outputs that any mild, other than for south and south west coastal areas, will make much further north. The potential is still there for snow for a fair number of places.

Cold air, once settled, has always, USUALLY, been very difficult to shift. So in the days when an outlook for 2 days was thought of as brave or now with the models giving a higher degree of confidence at that time scale and usually a reasonable idea, when one takes all the models, ensembles, trends into account, not just one model with one run, then the outlook is tipping back, it seems to me, towards a colder end to the year.

[JoeShmoe]

Just catching up on all the model hreads and seems some people have begun to equate this SSW idea with cold. Im sure its a valid teleconnector but is NOT the be all the end all else forecasting would be a breeze

In the meantine the GFS and UKMO 12zs are fantastic and snow potential up here right through until new year

[kold weather]

Yes UKMO at t144 looks to be going for the undercut which would be a snow heaven for the UK and then onwards to

the 06z GFS evolution there after and yeah I would take that.

Excellent synoptics again.

Yeah the 144hrs is very good, the LP would probably decay in place and split with a new trough being ejected eastwards and probsbly taking over. Also notice heights increasing near southern Greenland again, probably will be another cyclonic cold spell coming up soon after that.

[Thundery wintry showers]

Yes, this cold spell increasingly doesn't look like shifting for long. Even when it turns milder on Boxing Day, for Scotland and northern England "milder" will be a far better description than "mild", with showers in northern and western regions retaining a wintry flavour, and most upland parts retaining a large majority of their snow cover. The longer term outlook sees the southerly tracking jet play a major role once again, with heights rising to the north allowing an undercut with easterlies on its northern flank. What I saw as a two-day northerly toppler looks likely to upgrade into something more substantial, especially for the north- I have a feeling that GFS/UKMO are onto something here.

Southern areas are likely to see temperatures return to normal on Boxing Day and possibly stay around normal for a while, depending on how far north this undercutting low gets. But once that undercutting low gets out into the North Sea there's only one way all of that cold air is going to go, and that's south.

[johnholmes]

In terms of this cold spell and some of the comments about 'winter being over' from one or two at the end of November and early December its worth remembering just how well all the bits of the jigsaw fell into place towards the end of November and early December.

The major pattern change was correctly picked out by the two major models and they suggested it could last 10-12 days. Beyond that then the synoptic charts are unable to give solid guidance. definitely a feather in the cap of the two main models and their counterparts in the 500mb anomaly field, particularly the NOAA version which sometimes gets a bit of stick.

The longer term teleconnections also gave strong backing to what has happened.

So although many of us got burnt fingers last February-it does sometimes work!

[Geordiesnow]

UKMO keeps the -5 Uppers across most of the country Wednesday night , apart from the South coast. GFS has them higher so who will be right ? The UKMO has doner ather well this week .

GFS tends to handle upper air temps better than the UKMO, especially with Saturday's event where the GFS has the mild sector slightly bigger and further east than the UKMO.

Some good potential in the charts but that what it all is at the moment. It does look like there will be a north/south divide regarding the temps in the next few days but no-where should get too mild. i.e i can't see any widespread double figures appearing anytime soon.

[kold weather]

Ensembles are once again a very mixed bag, thier resolution probably won't be able to pick up the subtleness of the pattern, howver regardless they are pretty keen to give a +ve AO in early Jan, probably progressive but the models are really latching onto this idea...of course thats not to say we can't get a cold pattern even if that does happen....but still anything could happen for now!

[Zerouali lives]

If the 12z works out I can barelyimagine how much snow could be lying in Aberdeen this time next week.

There's already around 10" in the back garden and when that vicious looking bundle of 'weather' currenly out in the North Sea hits land we'll make it over the foot mark I'm sure. And then the northerly....

[Frosty.]

If the 12z works out I can barelyimagine how much snow could be lying in Aberdeen this time next week.

There's already around 10" in the back garden and when that vicious looking bundle of 'weather' currenly out in the North Sea hits land we'll make it over the foot mark I'm sure. And then the northerly....

Not much has been made of the Aberdeenshire Blizzards unsurprisingly as everything centres on southern and southeast england re media attention etc. You are right though, the cold air will probably stick up there and then be reinforced by another cold surge later in the weekend and more especially during next week, 12z runs so far suggesting another very wintry spell next week which could continue to reload as the gfs 12z suggests, I preferred the 6z though.