General Model Output Discussion

[Frosty.]

It's the turn of northern britain to have snow this weekend after largely missing out on all the action this week, it's only really the southeastern quarter of england which is likely to have significant snow tonight & tomorrow with up to 20cm on hills and drifting in strong to gale force ENE'ly winds gusting to 50 mph, maybe 4-5 inches even on low ground during the next 36 hours in the southeast. The 00z models have not changed much overnight with reasonable agreement that the arctic cold will be mixed out by boxing day at the latest, the models then show temps rising to near average but still cold enough on northern hills for further snowfalls.

Edited December 17, 2009 by Frosty039

[Nick F]

Morning all, the best charts for all us cold lovers is definately delivered by the ECM. Particularly good for snow on Christmas Day across the Northern half of the country. The big difference on this model is the rise in pressure over Svalbard, this hints at an extensive Arctic block that could prolong the colder scenario. The others seem to be quite progressive to introduce a more southerly air mass from next week, however ECM is delaying this progess quite markedly !

C

Yes, looks like the cold air will hold on across the N of the UK during next week, but across the south it seems increasingly likely that it will turn less cold and the wrong side of marginal. UKMO and GFS shows frontal system moving across the south Mon/Tues, this likely falling as rain though may turn back to snow as it clears. After that, looks like a showery regime, but any showers tending to be of rain across Sern areas with winds tending to come from the west.

[phil nw.]

The cold upper air will finally be across all areas by later today

http://charts.netweather.tv/gfsimages/gfs.20091217/00/18/h850t850eu.png

driven in my the stronger North Easterly flow.

The S.E. E.Anglia and parts of the E.Midlands are the highest risk areas for appreciable snowfall by am Friday.

The weekend is set to contiue v.cold with the flow backing to the North as an Arctic low moves towards the UK.

http://charts.netweather.tv/gfsimages/gfs.20091217/00/72/h850t850eu.png

The risk of more snow then comes from the north as fronts move south in the bitter cold air flow.

Signs that milder air tries to work into the sourh as we go into next week.

http://charts.netweather.tv/gfsimages/gfs.20091217/00/120/h850t850eu.png

This process looks slow though and not straightforward looking at T144hrs.

http://www.wetterzentrale.de/pics/Rtavn1442.png

http://www.wetterzentrale.de/pics/Recm1441.gif

http://www.wetterzentrale.de/pics/Rukm1441.gif

http://www.wetterzentrale.de/pics/Rgem1441.gif

Surface temps. still very low at this stage and slight differences in where the low complex situates could extend the cold untill Christmas or beyond.

[Rollo]

Nice summary Phil, it seems to me that the milder weather could well be delayed to nearer the new year than appears likely at this time but in the meantime lets enjoy ,for us, what will be a very welcome extended snowy spell.

[nick sussex]

Next week continues to look on a knife edge regarding further snowfall. The ensembles still have quite a few members prolonging the cold but the gfs operationals still look reluctant to go with one of these for the Xmas period. However several models at least keep the cold till just before Xmas.

The gfs 00hrs was a mild outlier for Xmas day and Boxing Day so there is still hope here, the further north the better though if you're hoping for either a white Xmas or at least having some snow on the ground.

The models group together like this after the 00hrs runs, wintry potential remains with the ecm, gfs, gem and no gaps, the ukmo and gme are poor in comparison with low pressure too far west.

Edited December 17, 2009 by nick sussex

[BLAST FROM THE PAST]

The stormy signal for the Christmas period will IMO succeed and lead us to less cold to evetually mild scenario. There is a signal for a whopper of a storm for New Year. Also something to look out for over Christmas is the chance of flooding in the southern UK through heavy rain and thaw conditions. It seems the models are grasping the breakdown scenario after this bitterly cold episode but we are off to the races as this winter is game on. Lets hope the snowy conditions over the next few days brings us a good delivery.

BFTP

[Frosty.]

The stormy signal for the Christmas period will IMO succeed and lead us to less cold to evetually mild scenario. There is a signal for a whopper of a storm for New Year. Also something to look out for over Christmas is the chance of flooding in the southern UK through heavy rain and thaw conditions. It seems the models are grasping the breakdown scenario after this bitterly cold episode but we are off to the races as this winter is game on. Lets hope the snowy conditions over the next few days brings us a good delivery.

BFTP

No flooding in the north then Fred?

It does look like a slow transition with perhaps the northern half of scotland remaining cold all next week.

[i luv snow]

The stormy signal for the Christmas period will IMO succeed and lead us to less cold to evetually mild scenario. There is a signal for a whopper of a storm for New Year. Also something to look out for over Christmas is the chance of flooding in the southern UK through heavy rain and thaw conditions. It seems the models are grasping the breakdown scenario after this bitterly cold episode but we are off to the races as this winter is game on. Lets hope the snowy conditions over the next few days brings us a good delivery.

BFTP

To be fair though, you're talking days away - a week infact! Im gonna enjoy the weather till Monday and worry about Fl later on

Edited December 17, 2009 by i luv snow

[BLAST FROM THE PAST]

No flooding in the north then Fred?

It does look like a slow transition with perhaps the northern half of scotland remaining cold all next week.

Breakdown will hit south first, north has chance of staying cold for a while longer. But there is going to be a lot of precip around. When the cold setup gives way I foresee a rapid change to thaw conditions, as quick as some GFS runs have shown but by then we would have had a week of freezing weather. The general rhythm of this winter is looking good though.

BFTP

[Weather-history]

The stormy signal for the Christmas period will IMO succeed and lead us to less cold to evetually mild scenario. There is a signal for a whopper of a storm for New Year. Also something to look out for over Christmas is the chance of flooding in the southern UK through heavy rain and thaw conditions. It seems the models are grasping the breakdown scenario after this bitterly cold episode but we are off to the races as this winter is game on. Lets hope the snowy conditions over the next few days brings us a good delivery.

BFTP

To be honest although I have articles going back to the Victorian times on this, I am not a great believer in weather by astronomy.

[TEITS]

ECM ensembles are less convincing if you desire a return to milder weather.

http://www.knmi.nl/exp/pluim/vijftiendaagse/Data/15DAAGSE_06260_NWT.png

The mean is lower than a few days ago and if anything the trend towards cold weather continues especially in the extended range.

[Yeti]

http://www.wetterzentrale.de/pics/Rmgfs634.gif

That's serious cold in Germany!

The GEM is nice because one of the Atlantic lows instead swings further NE through central Europe and misses the UK, keeping it cooler for longer and if anything dragging down a bit more cold air:

http://www.wetterzentrale.de/pics/Rgem1561.gif

There are also suggestions this morning of weak pressure rises over Scandinavia in FI. Tentative, but there on ECM, UKMO and GEM to varying extents - I don't know how this fits in with the teleconnections?

For example on the UKMO we see a cold pool underneath a HP cell moving SW towards Europe:

http://www.wetterzentrale.de/pics/Rukm1441.gif

[Barb]

The 00z op was quite a big mild outlier around the Christmas period. I don't think anything is certain yet.

[cooling climate]

There appears to me to be a shift further east with the low dropping down from the Arctic.

Hopefully this is a trend that will continue.

[Frosty.]

Breakdown will hit south first, north has chance of staying cold for a while longer. But there is going to be a lot of precip around. When the cold setup gives way I foresee a rapid change to thaw conditions, as quick as some GFS runs have shown but by then we would have had a week of freezing weather. The general rhythm of this winter is looking good though.

BFTP

Cheers Blast,

I was kinda hoping the cold would dig in more and last through next week but the writing seems to be on the wall as far as that's concerned although those ecm ensembles are interesting for sure. If I remember correctly, you did foresee this likely breakdown well before the cold spell began so hats off to you Fred.

[phil nw.]

Nice summary Phil, it seems to me that the milder weather could well be delayed to nearer the new year than appears likely at this time but in the meantime lets enjoy ,for us, what will be a very welcome extended snowy spell.

Thanks Rollo,

As others have said it`s a very unusual setup and any minor changes to the flow can make a big difference to the chance of the cold spell lengthening.

[Geordiesnow]

I'll certainly take the 06Z run in the short term any day and i think most people would aswell, there does seem to be a few mild sectors in Northern Ireland but i think you might still get away with it the cold at the surface should be cold enough. I think i'm right in saying that the upper air temp could be -1 and aslong at the surface it's still 0 or below, it would still be snow? Although i would imagine at the coasts, it will probably be of rain.

I still stand by my prediction that any breakdown will probably be between the 23rd-26th December, i'll be quite surprised if we are still in the cold air after that date but you never know with the weather. :wacko:

[Iceberg]

There appears to me to be a shift further east with the low dropping down from the Arctic.

Hopefully this is a trend that will continue.

That's a big change on the 06Z at such short notice and would prevent the southerlies a bit from coming in, maybe giving an extra 24 hr of cold for the south.

[TEITS]

The 06Z is clearly illustrating why beyond +96 isn't certain yet.

Looking at the +120 chart and I wonder if that LP over spain might move NE like last nights 18Z. If this is the case then anyone on the N/W of the LP would see heavy snow!

[Barb]

FI is +72 I think.

Yes that LP almost becomes a channel low but a bit too far south. I wouldn't be suprised if something like that happend next week though.

[nick sussex]

A really good gfs 06hrs run so far, initially the low from the north doesn't move as far sw and the low near Iberia heads ne, this is miles better than the ukmo, but we really need to see the ukmo fall into line this evening.

[Yeti]

The 6z is very similar to the GEM which I posted earlier:

http://www.wetterzentrale.de/pics/Rtavn1501.png

http://www.wetterzentrale.de/pics/Rgem1561.gif

The low heads NE into central Europe - this helps to keep the colder air over the UK as it lies on the western flank, and also it keeps northern continental Europe cooler which is a welcome surprise here!

[Barb]

What an extraordinary looking set up. Very messy. It'll be a brave person who says with confidence what will happen next week I think.

Edited December 17, 2009 by Barb

[phil nw.]

It`s really small differences in the placement of the surface features on the 006z which hold the cold in place to T150hrs.

The general flow is much the same and these small but important features are going to be a nightmare to model untill close up.

[johnholmes]

new and update Alert out