General Model Output Discussion

[David-kig]

This is becoming even more interesting, on the GFS 12z the cold air still covers the uk by T+264 hours with power to add, mild breakdown is nowhere in sight. is it safe to say that next week will continue either cold or very cold with snow in places and severe frosts with daytime maxima never gatting to more than +1c.

reload late in fl look at that

[Upgrade]

so Rob McElwee may regret saying it was "unlikely"there'd be a white Christmas last night on the news.

Yes Kold run by run it`s trending colder through to Christmas.

As the flow stagnates in that low complex we will get some really bitterly cold nights as the surface cold builds.

Unless some energy gets in the flow from the south West this will hang about for a while.

isnt it rare to get, stgnating, freezing cold low pressure systems stuck over us in winter? i don't think i've ever seen it before?

[Climate Man]

UK METO is OK, still chopping and changing beyond Monday next week though, so looking in detail at this isn't really worthwhile.

METO's own charts show the precip for the SW on Saturday night (approx 1am to 7am Sunday) as snow, possible for Cornwall and around the coasts (maybe 2 or 3 miles inland) is will be sleet, but both 1000-850 thicknesses and 850's and DP's all show that the majority of it will be snow.

Tbh I think this will be updated tomorrow to be snow(certainty for Somerset, Dorset, Wiltshire, Bristol etc).

A quick stab at Tuesday to Thursday show IMO that if you have snow on Sunday night then you will likely get snow in any of these areas for Tues/Thurs if you get precip.

If you don't have snow then you will be in trouble and would be unlikely to get more.

I do get the sneaky feeling that come new year we will be going through all this model watching again and trying to judge what the next cold spell will bring in the way of snow showers.

I am not sure that we will be looking for the next cold spell then. I am not convinced that this one will have passed. The GFS keeps trying to revert to mild in FI but the breakdown is continually pushed back. There is no reason why this should not continue.

[johnholmes]

lrf will be out this evening nd also the Xmas forecast with some comment on what I think the models are trying to show both in the short-mid term (up to and into the Xmas period) and the lrf for beyond.

[Climate Man]

so Rob McElwee may regret saying it was "unlikely"there'd be a white Christmas last night on the news.

isnt it rare to get, stgnating, freezing cold low pressure systems stuck over us in winter? i don't think i've ever seen it before?

He was put on the spot and rather than sit on the fence - chose to jump. If the GFS pans out, then the bookies may well be paying out.

[Frosty.]

I do get the sneaky feeling that come new year we will be going through all this model watching again and trying to judge what the next cold spell will bring in the way of snow showers.

It stayed very cold on the 12z gfs throughout, bit of an upgrade there with mild air nowhere close.

[Upgrade]

He was put on the spot and rather than sit on the fence - chose to jump. If the GFS pans out, then the bookies may well be paying out.

maybe the models have been at the christmas sherry .

there have been a few upgrades havent there now - the last 2 days seem to have been very positive for cold lovers across the board.

Edited December 18, 2009 by jimmyay

[Rob K]

That 12Z GFS run is pretty remarkable. If I am correct, the gridpoint temperature for the far north of Scotland is at zero or below for EVERY SINGLE CHART from T+6 hours right out to T+384 hours, day and night. I don't think that has ever happened before....

[SP1986]

Some of the nights minimums on this run are shocking. Either indicative that the new GFS model is too 'cold favoured' or that we may get a cold spell on the level of perhaps 1981. I just hope the models are having a fit.

[Frosty.]

reload late in fl look at that

We need the euros on board but the gfs is just prolonging the cold spell with no sign of a mild or even less cold breakdown. Scotland is in for a severe wintry blast during the next 4 days looking at the latest gfs, probably even worse than the southeast is currently experiencing..the lincolnshire wolds look like they are being blitzed with heavy snow showers at the moment according to the wonderful netweather extra radar.

[Methuselah]

Some of the nights minimums on this run are shocking. Either indicative that the new GFS model is too 'cold favoured' or that we may get a cold spell on the level of perhaps 1981. I just hope the models are having a fit.

I really don't know, Ste. But, if winds drop-out (as per GFS) and freezing-fog forms, there could be some very low nighttime temps? :blush:

[kold weather]

Under the snow cover, light winds, a very weak high pressure cell and moderatly cold uppers (-3/4/5/6s) then widespread -6/7/8s would probably be quite possible, I don't think we will go quite as cold as Dec 81 but the synoptics really do have a 81 ring to them at the moment...there are some events on the models which would normally suggest rain but the surface cold could be strong enough to at least make it far more complicated, esp in the south where things would be marginal past Tuesday/Wednesday...

[keithlucky]

so Rob McElwee may regret saying it was "unlikely"there'd be a white Christmas last night on the news.

isnt it rare to get, stgnating, freezing cold low pressure systems stuck over us in winter? i don't think i've ever seen it before?

So did john kettley he said no snow in south uk good chance in glasgow,what a bold statement for a week ahead.

[johnholmes]

Some of the nights minimums on this run are shocking. Either indicative that the new GFS model is too 'cold favoured' or that we may get a cold spell on the level of perhaps 1981. I just hope the models are having a fit.

I think you have a bit of a bee in your bonnet Stephen about GFS and its min temps, at least judging from the number of times you raise the issue?

Really the only way you can prove your point is to copy a chart of GFS mins and then show the actual values?

As others have pointed out-snow cover-light winds-little cloud cover and I too would be exceedingly surprised if several places before Xmas do not show double figures. Not widespread but over quite widely differing geographic areas.

But as ever we shall see over the next 3-4 nights how near or how far its predictions are.

-4 to -7C seems the general inland values for lowland inland areas and lower than this seems probable in some Scottish glens after thier snowfall this weekend, maybe evn the odd place further south?

[Rob K]

Some of the nights minimums on this run are shocking. Either indicative that the new GFS model is too 'cold favoured' or that we may get a cold spell on the level of perhaps 1981. I just hope the models are having a fit.

The GFS minima aren't really suggesting 1981-style cold. Back then there were -20s and even -25s in central England. The lowest the GFS has gone for in England has been about -14C I think. A few days ago there was a rogue -21 over Scotland following this weekend's northerly.

[Upgrade]

The GFS minima aren't really suggesting 1981-style cold. Back then there were -20s and even -25s in central England. The lowest the GFS has gone for in England has been about -14C I think. A few days ago there was a rogue -21 over Scotland following this weekend's northerly.

- 14 is still quite cold though. The big question is - will it snow?!

surely with all this low pressure around there will be precipitation and unstable air flows?

[Nick F]

I think you have a bit of a bee in your bonnet Stephen about GFS and its min temps, at least judging from the number of times you raise the issue?

Really the only way you can prove your point is to copy a chart of GFS mins and then show the actual values?

Quite!!

The active front dropping south tomorrow likely to bring widespread snow to much of the UK, and it doesn't look like weakening by the time it reaches the south, if anything GFS shows some intensifying on the eastern side of the UK.

Wishbone effect on Sunday and Monday, with most inland areas not exposed to the cold NWerly wind escaping the snow showers, though could see a Cheshire Gap Snow Streamer set-up. Possibility suggested by GFS early Tuesday of a front grazing the S and SE of England which may bring snow inland to these areas, though rain along south coast.

Beyond Monday though very hard to call for the rest of the week with a complex area of low pressure sat over Nern Europe with various centres moving around. Less inclination on 12z GFS for much milder air to reach as far north as the UK.

[Frosty.]

- 14 is still quite cold though. The big question is - will it snow?!

surely with all this low pressure around there will be precipitation and unstable air flows?

minus 14 is more than quite cold, it's perishingly cold, especially if there is a breeze. The GFS 12z suggests some minus 15's in scotland but imagine if it was mid jan, minus 20 or 25 surely.

[03jtrickey]

Wow just took a look at the Ensembles and I must say I'm shocked! The mean doesn't get about freezing throughout and not above -5 until Christmas Day. Good agreement on 850 temps up to the 25th, where there is more scatter, especially in terms of pressure. Nevertheless there is more agreement than I had expected to find! The cold spell was progged only a few days ago to break down on the 21st, then the 23rd, now it is indefinite. Odds on for a frosty Christmas I think.

[Climate Man]

There is a pretty nailed on snow event for most of the country tomorrow night and Tuesday is also looking very promising. Beyond that it is anybodies guess and none of the models have a clue. I have never seen such weird patterns and I guess the models have not either......

[Osbourne One-Nil]

Wishbone effect on Sunday and Monday, with most inland areas not exposed to the cold NWerly wind escaping the snow showers

Why do those charts show rain and sleet around the edge of the hole? I assume this is just an artifact if the way they compute these things?

I'm not concerned in the slightest, but just curious!

[pyrotech]

Can any on help with this.

Saturday nights event, for south wales is forecast to be rain!

ACccording to models 2m temps near 0, 850s near -5, 528 dam is beyond. I know its the warm sector but can not see why rain and not snow.

With all that in place would the dew point be above zero and if so what would be needed to drop dew points.

Can someone with model experience explain the reasons for forecast and about dew points (and where on models are dew points shown )

Edited December 18, 2009 by pyrotech

[len]

Can any on help with this.

Saturday nights event, for south wales is forecast to be rain!

ACccording to models 2m temps near 0, 850s near -5, 528 dam is beyond. I know its the warm sector but can not see why rain and not snow.

With all that in place would the dew point be above zero and if so what would be needed to drop dew points.

Can someone with model experience explain the reasons for forecast and about dew points (and where on models are dew points shown )

Arn't you confusing "dew points" with "wet bulbs". Snow requires a wet bulb of zero not a dew point of zero. With higher humidities in warm sectors wet bulbs are higher...hence more marginal for snow

Len

[Nights King]

Can any on help with this.

Saturday nights event, for south wales is forecast to be rain!

ACccording to models 2m temps near 0, 850s near -5, 528 dam is beyond. I know its the warm sector but can not see why rain and not snow.

With all that in place would the dew point be above zero and if so what would be needed to drop dew points.

Can someone with model experience explain the reasons for forecast and about dew points (and where on models are dew points shown )

I am also confused why the forecast is for rain in west country with low temps and values like that. would it be rain at 200/300m in south?

[pyrotech]

Arn't you confusing "dew points" with "wet bulbs". Snow requires a wet bulb of zero not a dew point of zero. With higher humidities in warm sectors wet bulbs are higher...hence more marginal for snow

Len

yes i am, so can you explain whats happening in that area that i can not see on models