General Model Output Discussion

[Barb]

Oh my the pub run has been on the Gin again, blizzard from undercutting low at +144.

[03jtrickey]

Marginal blizzard potential on this run - this time the fun is in the West! Thicknesses a bit high for prolonged snow though, could turn to rain? But one to watch?

http://charts.netweather.tv/gfsimages/gfs.20091216/18/153/h850t850eu.png

[East Herts Snow]

Oh my the pub run has been on the Gin again, blizzard from undercutting low at +144.

Where's Steve Murr....you could be right in the firing line of the undercutting low at +144?

If this run really were to verify, whoever stays on the colder North side of the Channel Low between +144 to +168 could experience some serious snowfall........, but run has to be an outlier, as the low is way too intense.

Edited December 16, 2009 by North Londoner

[Tom D]

Looks as if snow maybe at first in the west, then milder and wetter for a short time before possibly becoming colder again afterwards and the low moves north and east.

[Thundery wintry showers]

I think the GFS is going "off on one" as we head into FI-territory- there's no way we're going to get a low that deep meandering around south-east England! Nonetheless the trend is pretty good for cold/snow lovers. Saturday's event now looks like producing some significant snowfalls away from the west.

[kold weather]

We see an utterly classic cold at the surface situation on the 18z in the south, 850hpa temps look marginal, dew points look marginal but temps well below 0C as it arrives overnight pretty much keeps it as snow:

http://www.wetterzentrale.de/pics/Rmgfs1083.gif

http://www.wetterzentrale.de/pics/Rmgfs1084.gif

It then becomes a feeback situation as the snow would help to keep temps lower during the day then the GFS shows.

FWIW its also something a lot of the ensembles have been flagging up, so its worth watching as the ensembles have been keen on a marginal set-up for the south.

[Tucco]

18hr GFS. Blizzards for NE England at 180h. Could even be the expectionally rare severe blizzards for higher parts. Shame it wont happen.

Mark

Teesdale,Co Durham

[Frosty.]

18hr GFS. Blizzards for NE England at 180h. Could even be the expectionally rare severe blizzards for higher parts. Shame it wont happen.

Mark

Teesdale,Co Durham

Agreed, more likely the cold spell will just drain away with a gradual mixing out of the arctic airmass with milder weather slowly pushing north, the cold spell probably ending with a whimper rather than a bang.

[fear sneachta]

Imagine this treat for Christmas Eve!!

Edited December 16, 2009 by fear sneachta

[J10]

I think the GFS is going "off on one" as we head into FI-territory- there's no way we're going to get a low that deep meandering around south-east England! Nonetheless the trend is pretty good for cold/snow lovers. Saturday's event now looks like producing some significant snowfalls away from the west.

Snowfalls cannot be ruled out anywhere, with the warm sector factored to be further west in the FAX chart. Certainly any rain will promptly turn to snow on the back edge, and a real chance of heavy snow showers both into Saturday and into Sunday. I'd also take the GFS run for next week, but it probably won't turn out that way.

[karyo]

Snowfalls cannot be ruled out anywhere, with the warm sector factored to be further west in the FAX chart. Certainly any rain will promptly turn to snow on the back edge, and a real chance of heavy snow showers both into Saturday and into Sunday. I'd also take the GFS run for next week, but it probably won't turn out that way.

Yes, I agree! Rain turning to snow is the worst case scenario for western areas, so a covering is likely. I would prefer the precipitation band to come a few hours later but anyway...

The 18z ensembles haven't updated yet,still showing the 12z

Karyo

[nick sussex]

Agreed, more likely the cold spell will just drain away with a gradual mixing out of the arctic airmass with milder weather slowly pushing north, the cold spell probably ending with a whimper rather than a bang.

I think thats very unlikely given the set up, breakdowns from the sw are much better for at least some snow before milder air comes in, even then it will take a while and aren't as straightforward as projected by the models. You have to bear in mind how cold the continent is and will remain so till early next week, any se or even sse surface flow will be pulling in low dew points and cold air from northern France or the low countries.

Having looked at the ensembles interestingly Dublin and more northern areas has more support for the cold to remain, as you track east and south this reduces so we can begin to see an initial trend here, its not often you see an eastern USA type winter storm developing in the models, by this I mean a ne track from a much lower latitude, warmish air to the east with steep east to ne'erlies on the western side. We often see these causing all that mayhem across the pond.

So its at this point that the exact track and initial starting point, ie positioning of the low to the sw are crucial, its an impossible call next week because of this but possibly a quite rare set up, anyway its a developing situation and the models might just ditch the idea in future runs.

Edited December 17, 2009 by nick sussex

[Thundery wintry showers]

The slow retreat of cold air from the south relies upon the LP stalling to our west as shown on the UKMO and ECM- I think it is quite plausible but despite my earlier posts counselling some caution, I have my doubts about the likelihood of this Arctic low heading SW and stalling out west, as opposed to heading due south like on the GFS. We'll have to see what tomorrow's runs show, they could well show something rather different, such has been the trend (or lack of it, other than generally postponing the breakdown) over the last few days.

[Nick B]

I am curious about precipitation amounts shown for the Thursday / Friday scenario (for areas further inland).

We have the following seemingly about to verify:

1. Low 850's.

2. Low enough dam figures.

3. Good strong NEerly flow off the North Sea.

4. Dewpoints below 0 deg C.

And yet the showers are still shown to largely dissipate over the first 30 miles or so of land on the East coast. Bear in mind many senior posters were saying that under these conditions the showers would be significant and penetrate far inland giving good accumulations well into the midlands.

What has changed?

EDIT: I can see - it's the angle of the winds tracking across land after they come off the North Sea. See how much a very slight shift in the LP near the Netherlands has dramatically altered the whole of the next 2 days at least. Hmm...

Edited December 17, 2009 by Nick B

[The Enforcer]

I agree, Nick. On the radar, bands of showers already piling into Northern England where the easterly wind has already started.

Also, two fronts from an Arctic source across the country on Saturday and what does the meto warning page say? Nothing. Yet it has snow shower warnings for coastal districts for Sunday.

Edited December 17, 2009 by The Enforcer

[Nick B]

I agree, Nick. On the radar, bands of showers already piling into Northern England where the easterly wind has already started.

Also, two fronts from an Arctic source across the country on Saturday and what does the meto warning page say? Nothing. Yet it has snow shower warnings for coastal districts for Sunday.

I edited again... it's the very LP that was going to give us Round 2 (or actually Round 1 in this part of the world) no longer wants to! Maybe it will again on the 0Z but I doubt it...

[Thundery wintry showers]

I'm surprised at the lack of MetO warnings for Saturday- that has potential to produce a more widespread snow event than the Thursday/Friday NE'ly, though admittedly affecting the southeast (the home of the media) less.

Yes, a cyclonic NE'ly regime is often no good for inland parts of the south as they end up with what effectively ends up as a northerly with an easterly source- this happened also on 28 December 2005.

[kold weather]

Yep that cold front looks like it could be interesting and could be quite active looking at what I've seen from some runs. Also something which the 18z has finally introduced but has been advertised for a while on the ensembles is the chance of a frontal system forming behind the one coming down from the north in the Channel/N.France, then as the flow turns more southerly the front is pushed into the south. The 18z GFS shows us a rather extreme verison (one that I'd have few doubt that those away from the far south would get quite the dumping on) of that solution but its been something that the ensembles have been very keen on.

[wellington boot]

I have to say, I think the 18z is probably going to be the closest to the solution out of all the charts we've seen so far. This is not a ramp by the way, as I am not convinced all that many of us will do very well out of this situation, but I do see our big arctic low drifting slightly west of centre and then at least one lp moving up from the south west as suggested here.

It is a pattern we've seen many times before. We'll probably get some amazing runs in which it tracks down the channel and arrives at night and dumps on everybody, but as we get closer to the time, it will be progged further north and west, until it's only the north western half of the uk who might get anything out of it.

This said, there is plenty of cold air about, and if snow has come previously and cooled down the surface, and if the hp to the north/west remains reasonably strong, as, uncharacteristically, it looks like it might, it is possible that we might get some sort of reboot out of it. Lots of ifs and buts.

In any case, I think this kind of pattern, with possibly a fairly potent lp spinning up from the south west and drifting across the isles, is a distinct possibility.

[anvilhead]

a low of 959mb moving ne across Cherberg monday, gale force winds across the south uk - I imagine this would be a phenominal blizzard but it looks to be tied in with a very complicated, convoluted jet over our parts so unfortunately dont really see it happening. I would bank this run though souley for that event ..

sam

[KTtom]

Quiet in here? Excellent GFS this morning plenty of ppn over the weekend as bands of snow move west to east as the low slides down the western side of the country. Fax @120 hrs and UKMO is poor though in the extended timeline as the low is further west and starts to introduce southerlies by Monday, as others have said the surface cold is still there but in terms of breakdown the worst scinerio as it would be a gradual warm up. In the meantime a very wintry weekend in store for all.

[Iceberg]

Good ensembles this morning from GFS keeping even 850s surpressed (thicknesses will be generally lower relatively speaking), Dorset Ens has us struggling to reach over the -5 as the mean and even then only very slowly next next.

Good ECM as well IMO, with the milder weather being delayed until at least Christmas Eve, but even then being a slow progress.

The noticable thing from both the ECM and GFS is how quiet overall the Atlantic is, to have an LP moving westwards like this is far from the norm.

The snow still looks on course for this weekend (for 95% of the country) on the METO, GFS and ECM precip charts at 72Z.

Meto again is very different at 144Z to GFS and ECM, one example is the Scandy high it develops again at 144Z, GFS is having none of it and ECM is pretty indifferent.

It looks as though the ECM is the middle ground and is probably the model I'd pick for upto 168Z and very good that would be too !.

Longer term between Christmas and New Year I still fancy an easterly occuring, or worse ase HP to settle over the country.

[Snowmad79]

The charts dont look bad too me and the breakdown is still in up in the air so speak. The ukmo doesnt look good but the GFS shows a brief burst of sotherlies before heading towards an Easterly type senario at the end. The Ecm out to 192 also shows a brief burst of westerlies then south easterlies before the LP moves NE putting us into an easterly type flow.

Edited December 17, 2009 by Snowmad79

[suffolkboy_]

Longer term between Christmas and New Year I still fancy an easterly occuring, or worse ase HP to settle over the country.

Either way the cold is never far away if it does leave completely at all. Plenty of potential for an Easterly reload with the Atlantic very quiet indeed.

If high pressure was to settle over the UK then very low temperatures, even record low tempuratures would be recorded with some of the longest nights of the year and snow cover remaining in many areas.

[carinthian]

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