General Model Output Discussion

[Polar Continental]

You were right TM, the ECM not quite as cold, just about gets us through Christmas before becoming milder. The UKMO is better with possible snow on Christmas day and a north easterly to follow. The GEM is more in line with the ECM, showing a breakdown around Christmas.

[Tim Bland]

http://www.wzkarten.de/pics/Rukm1201.gif :lol:

Can I have this for Christmas please Santa!

Just thought, Its countryfile this morning! Wouldnt want to do that forecast with so many different options on the table. Will be a streesfull few days at the Meto as media will be hounding them with whether it will be a white christmas or not (along with the bookies)I think the models are struggling as this is such a unique situation for the UK

Edited December 20, 2009 by Tim Bland

[SLEETY]

You were right TM, the ECM not quite as cold, just about gets us through Christmas before becoming milder. The UKMO is better with possible snow on Christmas day and a north easterly to follow. The GEM is more in line with the ECM, showing a breakdown around Christmas.

Ecm in fl land is very interesting again,with the Artic high building South again.Glacier points theroy that its January when the intensely cold weather hits,appears to be on track with the current ECM output.

Keep those snowboards on hand guys

Edited December 20, 2009 by SLEETY

[Terminal Moraine]

You were right TM, the ECM not quite as cold, just about gets us through Christmas before becoming milder. The UKMO is better with possible snow on Christmas day and a north easterly to follow. The GEM is more in line with the ECM, showing a breakdown around Christmas.

Yes, Paul, although as Sleety mentions, the ECM in its later stages is not too far away from the GFS, a less well developed ridge from the Greenland high but with the high well in evidence.

Let's see what the 06z throws up.

[Frosty.]

The GFS 00z gets very close to some spectacular wintry synoptics in FI with that reload from the northeast and holds the cold block in most areas throughout with a fine and very frosty spell in the north & east post xmas before that NE'ly blast. The ukmo 00z is very nice with lows further south and a cold E'ly feed, even by T+144 the ukmo shows no sign of a mild breakdown. The big let down is the ecm which again goes pear shaped after xmas day although perhaps some cold air would linger in the far north with possible snow for parts of scotland when that low moves in later, if it wern't for the slightly rubbish ecm I would be happy with our chances of the cold spell continuing beyond friday...pity.. but, with such a complex pattern, small changes in low pressure position and track will make all the difference.

[Polar Continental]

Ecm in fl land is very interesting again,with the Artic high building South again.Glacier points theroy that its January when the intensely cold weather hits,appears to be on track with the current ECM output.

Keep those snowboards on hand guys

Yes, Paul, although as Sleety mentions, the ECM in its later stages is not too far away from the GFS, a less well developed ridge from the Greenland high but with the high well in evidence.

Let's see what the 06z throws up.

Yes most years by this time in winter the polar vortex is well in evidence over Greenland and stays there until spring. This year it cannot seem to settle at all, so I think as a consequence the models are having a hard time trying to get a grip on what may happen, even in what would normally be a reliable time frame.

Some very interesting times ahead, even exiting, what we are seeing now on the models has been the stuff of dreams over recent years, this time it may all becoming true!

[Lincs Observation]

Morning all

I think its fair to say that the Models are really struggling with the outputs at this time also struggling with agreement, like someone mentioned the BBC Forecast for the week ahead looks like an interesting one for sure. Ever the optimist though im taking such variation as comfort that Maybe just Maybe we could hold on to the cold for longer than we would normally do. What i mean is that it could be the colder scenarios that is making it a headache for the models, It would be interesting to see if the models for the 80's would give us a better idea of evolution based on the fact some compared patterns of late to similarities to Dec 81 i think.

I Know im clutching at straws with an alternative angle to look at, however with Europe all the way down to Northern Spain & North America struggling with the cold weather i have a hunch that this could be an exceptional winter unseen for some 20 odd years and the models just dont know how to handle the odd climate pattern.

[Snow storm]

The 00Z is very good for those up North. You may well have a solid week of snow showers, with temperatures very rarely exceeding 0C.

For us down South it is going to be nail biting!

The 528 dam line flirts with the south, on numerous occasions and the day time temps are actually quite low, with maximums between 0-3C inland, but a barmy 5C on the South coast (the contrast in temperatures from 5C to 1C in the movement 20 miles inland is remarkable, and is down the fact that there is an Atlantic low tinkering with NW France, rotating mild air on Monday.

I am not going to get my hopes up for the South, because generally in marginal situations the South rarely gets a good dumping, it normally takes cold continental air or a good northerly plunge to get temps down, otherwise most end up with rain.

One interesting thing about this run is all the PPN in the English Channel, can any one on here identify why this is?

[tinybill]

morning all i know its fantasy land and f1 is the gfs saying the beast will be back just in time for all of us to struggle in to-work !!!

[Stu_London]

Intruiging model output this morning.

Makes you wonder how much of the 70s and 80s snow events that came at short notice were down to lack of technology/poor forecasting and how much was down to the sheer unpredictability of the various scenarios playing out.

We have seen this week how the supercomputers have really struggled with what we consider to be in the short and reliable range (72 hours).

To be fair though, I think the GFS and their ensembles nailed the cold spell exactly how one would expect it too which a gradual increase in cold members with the detail changing. The high incidence of the operational run (and parallel at the time) chucking out a cold scenario was a bit of a giveaway too. Much to learn for the future I think.

Two areas of interest at the moment

1 - The breakdown - mildest case scenario looks like a breakdown for the south over the Xmas period spreading slowly north, however all options including no real breakdown remain a possibility (the 00z GFS offers the best possibility of this - pressure over us and to the NE would need to be higher however)

2 - The next cold spell - Using the ensemble method - somewhere around the 30th December would be of most interest at the moment - the period needs an eye kept on it.

[NorthNorfolkWeather]

Intruiging model output this morning.

Makes you wonder how much of the 70s and 80s snow events that came at short notice were down to lack of technology/poor forecasting and how much was down to the sheer unpredictability of the various scenarios playing out.

Hi Stu,

That's a very good point, we look at the models and, in most cases T+96 or T+120 is where is all starts going a little pear shaped, and that's with computing power that was unheard of a few years ago. At this point, I don't think we can safely call anything confidently after T+60. But most of this is down to the fact that the models can only cope with the data they have, and most of that, for the UK is zonal, so every event like this will help future predictions when we get events,like the Polar vortex becoming so disrupted, that causes downstream events 4-6 weeks after the initial change. I think that people like GP give us a fantastic overview on these things that would not have been possible even a few years ago.

"The Butterfly Effect" was first mentioned ( in my memory anyway) in the late 70's, the ensembles illustrate wonderfully how a very small input change leads to huge downstream changes. Look what happens after 60-72 hours, huge variations

In conclusion, we still don't know when we'll have a breakdown to mild conditions, and don't even look at FI

[Guest North Sea Snow Convection]

Very easy to look at the models from an IMBY perspective atm. On that basis then it looks very disappointing and less cold with rain at times, or in the case of ECM much milder. The only much more interesting prospect is the UKMO which continues to want to orientate low pressure much more favourably to hint at an easterly - but nothing more than that atm

However from a national perspective then a fair chance that the current cold air will hang around with more snow very likely for northern areas, again excepting the ECM which wants to take mild air northwards and end the cold spell almost everywhere over xmas.

Longer term, still height rises suggested to the far north, but with troughs very close by to the British Isles and to the south west - no real signal of another reinforcing cold reload - execpting perhaps the UKMO.

The cooldown in the stratosphere suggests the polar vortex perhaps becoming more organised, which isn't going to help at all in terms of blocking to the north- and as suggested before, there is a need for a proper warming event there asap to enable another arctic reload

Edited December 20, 2009 by North Sea Snow Convection

[East Herts Snow]

Charts at +108 show quite an intense low off the Kent Coast (further West on this run). 528 Dam line across the Midlands, could be a lot of snow to the NW of this low.

At +114 low moves further East and brings the 528 DAM further Southeast and with it the chances of snow for some areas on the big day.......

Upgrade alert for Christmas day for potential snow....

528 DAM clears whole country and more PPN on this run, could it be a white Christmas for Southeast?

Edited December 20, 2009 by North Londoner

[Tom D]

Charts at +108 show quite an intense low off the Kent Coast (further West on this run). 528 Dam line across the Midlands, could be a lot of snow to the NW of this low.

At +114 low moves further East and brings the 528 DAM further Southeast and with it the chances of snow for some areas on the big day.......

Upgrade alert for Christmas day for potential snow....

528 DAM clears whole country and more PPN on this run, could it be a white Christmas for Southeast?

I don't think so, uppers are too warm and surface temperatures around 2c across southern England.

http://charts.netweather.tv/gfsimages/gfs.20091220/06/123/h850t850eu.png

GFS max temps for 26th in Scotland still below 0c despite a big low pressure with uppers of -5c and plenty of precipitation and strong winds moving in. Could be a big dumping before the milder air takes control.

It's a long way off yet but the GFS is adamant that the Atlantic will come back during or after Christmas Day.

Edited December 20, 2009 by Tommyd1258

[January Snowstorm]

06z is a shocker if you want the cold to hang on

It's now very clear that from Christmas day on it's back to normality

[East Herts Snow]

I accept what you are saying Tommyd1258, but this still may make Christmas Day interesting at the very least for some areas, as the below may point out.

If this run were to verify, Christmas Day could be brilliant for a lot of the country, in particular the Southeast

528 Dam across the whole country....

Plenty of PPN around...and look at how tight those isobars are across the SouthEast, coming off a warm sea, could be a repeat of the snow event last Thursday.

However there is a warm sector to the low across parts of Kent, however if this was to move further East.

Ground max temperatures maybe a tad too high especially near the coasts

NB - On Betfair only one snow flake falling over Buckingham Palace weather centre constitutes as a white Christmas.

Edited December 20, 2009 by North Londoner

[Mark Bayley]

06z is a shocker if you want the cold to hang on

It's now very clear that from Christmas day on it's back to normality

Doesn't look back to normal to me, well not the bog standard raging mild south westerlies. Still looks cold in north for most of the run. The south turns a little milder for a time but that's about it! Then in deep FI it turns much colder again. So i can hardly see this run being a shocker compared to past winters!

Edited December 20, 2009 by mark bayley

[Tom D]

I think you need to bear in mind what constitutes a White Xmas Tommy, 1 flake of snow in the 24hrs of Xmas Day, obviously that one flake can be amongst 99.99999% rain. Based on this the 06 GFS keep the chances of a White Xmas very much on for almost all areas, even tho deep, crisp and even does not at all likely away from northern hills.

It would be typical that it would be a 'white' Christmas with sleet, which would likely melt the ground snow! Oh well, the bookies could be paying out a lot of money! :lol:

It's a long long way off, but this chart looks vaguely familiar...

http://charts.netweather.tv/gfsimages/gfs.20091220/06/384/h850t850eu.png

Edited December 20, 2009 by Tommyd1258

[mountain shadow]

06z is a shocker if you want the cold to hang on

It's now very clear that from Christmas day on it's back to normality

What? based on a GFS 6z Ops run?. I seem to remember a similar cry of despair after

a GFS 6z Ops run about this time last week. Only for it to be far from the mark.

With such differences between the three main models at t+120, and the Arctic High coming into play, anything can happen.

[TEITS]

I think you need to bear in mind what constitutes a White Xmas Tommy, 1 flake of snow in the 24hrs of Xmas Day, obviously that one flake can be amongst 99.99999% rain. Based on this the 06 GFS keep the chances of a White Xmas very much on for almost all areas, even tho deep, crisp and even does not at all likely away from northern hills.

For me personally I define a white xmas if snow is lying on the ground. Now considering away from the SE the temps look to remain near or below freezing, those who have a few inches of lying snow have an excellent chance of retaining this snowfall. I have no doubts that in my location it will be deep, crisp and even on xmas day which will be the first time since 1981.

As for the models, well only one word to sum these up and that is volatile. The difference between the 12Z/0Z ECM is extraordinary. Looking at the GFS/UKMO the ECM at +144 looks very much an outlier.

[TEITS]

What? based on a GFS 6z Ops run?. I seem to remember a similar cry of despair after

a GFS 6z Ops run about this time last week. Only for it to be far from the mark.

With such differences between the three main models at t+120, and the Arctic High coming into play, anything can happen.

Unfortunately some only remember the downgrades and never remember the upgrades. Lets remember that at one stage the models really downgraded the E,ly before upgrading it once again.

[snowingman]

its all to play for over the Christmas period, certain now to be cold right up until the day itself - after this models don't seem to have a clue¬

[Terminal Moraine]

A very interesting 06z GFS post christmas day. Milder air battles its way across England and Wales temporarily, there's even a deep little secondary at one point, but the cold eventually returns in time for new year.

I'll be interested to see the ensembles when they come out as the 00z was among the colder members at that range.

The current synoptics have all the characteristics of the cold v mild battles of winters in the 60s, 70s and early 80s.

[Joneseye]

How anyone can say with any certainty what is going to happen in 5-6 days I don't know. In all my time of model watching I haven't seen synoptics like we have at the moment except in archives.

The 06 GFS throws yet another scenario into the mix. As Tamara stated earlier it is quite easy to look at the models from an IMBY perspective and from my own it paints a marginal picture with the threat of precip and cold temps and reasonably cold uppers. It snowed here the other day with an upper air temp of -3.6 with a +1C temp 0C dew point and light precip so I will take my chances with marginal thankyou very much.

Into FI on the 06 GFS it shows a messy breakdown with the main low pressure held out in the Atlantic.. not sure how plausible that is!?

[snowingman]

UK office charts show a little nasty low appear in S Ireland on 24th Dec - this could be very interesting if it moves across S Uk - Major white Xmas for some?????

you hear it here first!