GFS t168 to t192, Dec 5th and 6th, and the pattern change prior to it and during it is still in FI land.

At T144 Good that we see the Cen. N Atlantic &UK High drift West, we SE that it will bring a NW flow on T168 and later at t144hfs (GFS).

Then at T168 to T216 we see Cold Low Pressures Iceland and number two to join it it come in from NW N Atlantic, the merge on Thurs 5th and a mild rain Sector crosses UK, which then leads to the Second part of merged Low Pressure- Cokd and snowy weather on p.m. Thurs and Wintry with frosty weather and heavy snow showers for most UK areas by Friday the 6th December and last through 7th and 8th, this few days Arctic plunge Northwest then Northerly needs 7-8 days monitoring to put the confidence we need the GFS - keep watching it run by run.

It has the West N Atlantic High merge with Greenland High during the event, it GFS then brings end of it by the Tuesday Wednesday of Dec. 2013 week 2.

I look FORWARD to any good news.
It would end by seeing a large Greenland Low bring Westerly flow from our West and NW!.

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For one minute I thought I was in a geography thread

http://www.wetterzentrale.de/pics/Rtavn2282.png

http://www.wetterzentrale.de/pics/Rtavn2402.png

http://www.wetterzentrale.de/pics/Rtavn2522.png

http://www.wetterzentrale.de/pics/Rtavn2642.png

Some cold air across the UK

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The NAVGEM and GEM are great! With all the cold air coming over to the atlantic side, some unseasonably low uppers could get towards the UK in this cold snap. 

Now the SSTs are still very high at this time of year

http://www.bsh.de/aktdat/mk/nordsee/actual.gif

and are, roughly about average for the time of year.

I think I said a while back how heavy snow is much easier to get early on. This is a pretty good example:

if -10C uppers were to get down across the north sea coasts generally, with a 10C ocean, that is a 20C gradient to the 850 level. Now, you generally need 13C gradient to initiate lake effect precipatation, above 17C and you can get some really quite heavy showers. And above 21C thundersnow becomes common. It is quite concevable that some northern areas will meet this benchmark with uppers perhaps as low as -13C in the far north, and -11 or -12 more generally; giving perhaps a maximun of a 22C temp gradient.

A 22C temp gradient, would be capable of producing 10cm/h + rate snowfalls. Note, I am not saying 10cm will fall every hour, but the core of the showers could be well above a 10cm/h rate, even perhaps getting into the 20s in the heaviest showers. And we might also expect to see lifted indicies getting towards zero. Thundersnow would be on the cards if everything else plays right (the wind is perhaps too northwesterly, a slight easterly component is probably needed). 

http://www.meteociel.fr/modeles/gfse_cartes.php?mode=11&ech=204

Indeed, look at the 216 chart and notice the blues.

I made a thread a while back where I looked at observed values of CAPE in lake effect snow for the UK. You need a cape of about 150j/kg - 200j/kg for thundersnow. That is somewhat evident here. 

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Or even the Bering Straights


[sic]

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Ooh, a nice slider at T+288 on GFS - with lots of sliding on the ground to follow

High pressure then drifting over Britain with milder air aloft - but perhaps an inversion as cold air gets trapped close to the ground over the snowfields of southern England?    One can dream....

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Danish, not Dutch (just to complete the pedantry!) 

 

GFS 12Z is also rather chilly around Dec 7-10, as was the 06Z. Both runs also showed potentially snowy lows crossing the country, although the detail was quite different. If the 18Z follows suit then I think we can call it a trend... 

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GFS 12z: Very interesting to see blocking to the NW followed by an Arctic-origin Siberian High almost getting in on the act.

It still lets LP through the Bering High though, which UKMO doesn't. With the LP deflected south as per UKMO, the potential in the 7-10 day range is even greater.

I sure miss having the time to analyse this in depth!

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After the fiasco a few weeks ago, GFS seems to be leading the way on this "cold spell" which is a good sign.

 

 

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 Will be handy  just noticed extended 850,s  now availabe for ukmo to T144

http://www.meteociel.fr/modeles/ukmo2.php?nh=0&ech=144&carte=1007

 

was I think to t72 as on wetter I think.

 

ECM so far

http://www.meteociel.fr/modeles/ecmwf/runs/2013112712/ECH1-192.GIF?27-0

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Yes, the GFS model has hinted at a cold snap/spell around the 5th to the 7th of December for a number of days now. Up to 70% of the ensemble members now show snow here at the very end of the hi-res section.

Given Met Office forecasts and model output I would say, barring sudden changes, a cold spell of some form is likely towards the end of the first week in December.

Now, just watch the ECM 12z show something totally different!😊

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looks like a toppler from ECM. No sign of pressure sustaining  like on the 00z

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Ouch. So different from the 00z. We get the cold snap but then back to square one

 

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yep , ECM not having it

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The positive for coldies is there is no moderation in the projected spell next week, although there has been a shift in timing which happens quite a lot at this range.
The 12Z GFS cluster is actually quite impressive for a few days with the OP now joined by several members bringing -8/-9 uppers down to 51deg N. These values, other parameters allowed, are sufficient to support snow to low levels but as usual it'll be in the form of showers to coastal areas and more generally the North.

I concede that I have adjusted my expectations for next week, and if trends continue, I amy have to adjust again.

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http://www.theweatheroutlook.com/charts/gefs/gefsens850London0.png

Some agreement of the downward trend in temps around the 3rd, OP was a cold outlier after 9th .

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Should that not be bering any sudden changes 

The trend is excellent, lets hope that the 1 lone outlier perturbation issue from a few years ago doesnt crop up nearer the time 

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Thought this board would be in mini meltdown, but shows how we have been spoiled in recent winters, but the caution is sensible.
Cold outbreak getting near the reliable
http://www.wetterzentrale.de/pics/Rtavn2642.png 
http://www.wetterzentrale.de/pics/Rtavn26417.png 

To be fair, the 00z ECM Op was one of the colder options in the Ens in the mid to long term. The 12z Op lies comfortably in the options shown in 00z Ens pack, so not really a massive shift in outlook. Let's see what the 12z ECM ens show.

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ECM as so often is the spoiler, showing a glancing blow of cold before the high topples across the UK. It would certainly be chilly but not a lot else. http://www.wetterzentrale.de/pics/Recm2401.gif

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I think you'll find that ECM has been showing the same evolution since it came within range.

The pattern is still a bit mobile but ECM 12z delivers a 3 day cold spell (lasting into Day 11, looking at the evolution).

As always it will be interesting to see where the ensemble mean sits - generally the Op and Mean are well aligned out to Day 6-7 at least.

 

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Hi everyone. Here is the report on the 12 noon outputs from GFS, UKMO, GEM, NAVGEM and ECM for today Wednesday November 27th 2013.

All models show a large High pressure area close to SW Britain and a mild and moist but light cloud laden NW flow over the UK. This pattern remains for another 36hrs or so with just very weak fronts injecting a little more moisture into the atmosphere at times with a little drizzle. On Friday fresher and chillier NW winds blow down over the UK as the High moves a little further away West briefly allowing some showers to occur, perhaps wintry on Northern hills for a time. By Saturday the bright and fresh weather will slowly become eroded from the West by milder Atlantic air, toppling back down over the UK with High pressure close to Southern Britain. As we start next week the High pressure slowly recedes away South or SE but maintaining a ridge across the UK well into the middle of next week maintaining dry and rather cloudy weather with temperatures close to average for many with only limited amounts of fog and frost by night should skies clear.

GFS then shows Westerly winds steadily increasing later next week with some rain gradually winding it's way South across the UK reaching the South later on Thursday or early Friday with very much colder and brighter weather following down with wintry showers and strong winds giving some very wintry conditions over northern high ground for a time and even some wintriness in the showers over the South too for a while. Over the weekend conditions moderate for many but it would stay cold with a disturbance as shown bringing rain across the South a week on Sunday and some snowfall in the North before this shifts away SE as pressure builds strongly from the West later. Innitially this could mean some very sharp frosts for a few nights early in the second week before an inversion develops with an infill of cloud setting up a cloudy and benign pattern to end the run with the mildness returning to the North in Westerly winds while High pressure remains straddled across the South.

UKMO tonight shows High pressure in mid Atlantic with a ridge extending East over the UK with quiet and benign weather continuing at this stage with a lot of cloud, largely dry weather and temperatures close to average.

GEM tonight shows a trough bringing a spell of rain SE across the UK next Wednesday followed by another surge of High pressure transferring slowly SE across Southern Britain and away to the SE towards the end of the run. A deep and slow moving Low pressure well North of Scotland sends some rain and strong winds across Northern Britain. A weakening band of rain on a cold front then swings SE across Britain followed by colder weather with wintry showers across the North but mostly dry weather further South.

NAVGEM shows a weakening front too moving SE over Britain next week with some rain for a time before clearer and fresher weather moves in behind followed by more unsettled and windy weather reaching the NW later.

ECM tonight shows a cold front running South again late next week with a short spell of rain followed by some wintry showers, more especially in the North and East, heavy briefly. Quickly following is another major rise of pressure with the UK returning to dry and benign conditions with frost and fog prior to milder air toppling back into the NW soon after Day 10.

The GFS Ensembles show a change to colder conditions soon after midweek next week with a 3-4 day colder interlude before things recover to average levels. It is unlikely that any major snow events will occur over the South with most of any wintry action reserved for more Northern areas before things revert to milder weather towards the end of the run from most members.

The Jet Stream flow shows it's axis carrying it well to the North of the UK around the Northern flank of High pressure to the SW of the UK. This persists for the reliable part of the output tonight before in the less reliable period it shows signs of migrating South across Britain, then resetting across Britain from the West. In the far reaches of the run it then is shown to extend back North across the Atlantic towards Greenland and Iceland.

In Summary tonight the weather remain very static over the coming 7 days. Beyond that things do turn more interesting for a while as a cold plunge of Arctic air moves down across the UK from the North. There is a strong risk of snowfall over the North for several days mostly in the form of showers while the South is generally unlikely to see anything exciting before fine weather returns in association with more Atlantic High pressure. After some frosty nights towards the end of the second week it looks like milder Atlantic air with High pressure close to the South looks the most likely end result.

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Really?  The 850hPa charts show values for London:

Day 9: -6.5C

Day 10: -7C

Day 11 will be similar as the high topples slowly across.

500-1,000 thickness values are down in the mid to low 520s.

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ECM doesn't look too bad towards the end. It's clearly struggling with a sudden massive drop in pressure over Greenland within 24 hours in FI

Some sort of cold snap or shortish spell looking increasingly likely, although still plenty of time for things to go wrong yet

Little bit frustrating to see residual energy from the PV still right across the far North - at this stage very much looking like a temporary blip before we return to probably HP dominated weather again until the next window for ridging North occurs. Still wasn't ever shown to be much more than this anyway so not like it should be a surprise or anything.

 

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