General Model Output Discussion Thursday December 24Th:

[swilliam]

Comparing this run of the models and the 12Z run yesterday not much has changed really. For early next week we are still looking at the exact positioning of the LP to the SW and the angle of the trough extending East from it. Looking at the ensemble for the Midlands there are still are fair few (including the OP) showing a more Northward position and the trough extending NE sending up mild air over the South and Midlands.

There is then even firmer agreement for the cold NEasterly early in the New Year. We then have the large scatter depending on the setup of the blocking anticyclone - cold if it it initially sets up towards Greenland or later retrogresses NW, mild if it sinks towards us (like the control run - although even that still keeps us cold but with less snow potential). I think there are more members going for the 1st option this time so encouraging signs.

Edited December 24, 2009 by swilliam

[Guest North Sea Snow Convection]

The ECM and GFS are both consistent with ridging towards Greenland in around a weeks time and I believe that this will occur to a more or less extent. However, differences lie in the modeling of the polar vortex. The ECM has a far more favourable outcome with the main vortex being displaced before dropping into Scandinavia. Things are not quite as clear cut with the GFS with a more disorganised approach with the main vortex being situated near Baffin Island. These differences will be ironed out as New Year approaches but could vitally be the difference between a cold pattern or very cold pattern emerging. Lets see what the GFS 6Z shows.

Thats a good point - the ECM seems to be following GP's analysis though!

[cooling climate]

Temperatures overnight according to the GFS 06z run are expected to be around 2c over east Midlands, east Anglia

and central southern and southeast England.

I wonder with precipitation forcast and dew points around +1 with a little help from evaporation cooling could we

see some snow in these areas, if only to win my £10 bet of snow on Christmas day in London lol.

[ribster]

Yes its mild mild for the foreseeable future in the south with that mild heading north around sunday

Anything else is F1 im afraid although its fun to look at year end charts

We need things to get into T96 before we talk with any confidence, as we have seen in the last few weeks T144 or T168 is often miles out to what happens

Absolute tosh, the chart SMM shows is for the 29th, which in my book is also FI and subject to change. At best temps will briefly recover to around average. However, as West and others have stated the general theme (FI or not) is for cold, in fact the charts have been and still are remarkable. I posted up a chart a couple of days ago from the GFS 06z from the 2nd Dec - for the 17th, which pretty much verified - yes there were changes, but it nailed the theme very early on.

[Barb]

Wow the 06z is brilliant for Wales for early next week - massive snowfall as the the boundary is further south than 00z - more inline with ECM,GEM and GFS ensembles. Might have a foot if that came off.

On a knife edge though, as usual.

Probably will come down to nowcasting.

[cooling climate]

Out to t120 and it looks like the link between the ridge in the Atlantic and the heights up north will occur on

this run.

This should therefore be a very good run for cold and wintry weather fans.

[nick sussex]

A better gfs 06hrs run compared to the 00hrs, here the low to the sw is better orientated and this looks quite similar to the ecm 00hrs, NOAA have gone with the ecm 00hrs and ecm 12hrs ensemble mean from yesterday in the morning discussions which is nice to see.

Edited December 24, 2009 by nick sussex

[BLAST FROM THE PAST]

Even with a less cold/average spell arriving for the south, and even with a mild day or two chucked in, there is no 'mild' in the picture. What I mean by that is that the hemispheric pattern is a cold pattern and its just a shuffle and reload going on. The cold WILL win, and comparisons to past great winters are very realistic and talk of cold not really getting to the UK from true cold sources were for me dispelled last year and certainly are now. Interesting mini battle going on again with the ECM and GFS over New Year...which will be right?...did the GFS win the last round?? I favour ECM as first blizzard [1st of four] to strike on 3rd Jan for all UK [as north half may get one on the new year storm]

BFTP

Edited December 24, 2009 by BLAST FROM THE PAST

[TEITS]

Wow the 06z is brilliant for Wales for early next week - massive snowfall as the the boundary is further south than 00z - more inline with ECM,GEM and GFS ensembles. Might have a foot if that came off.

On a knife edge though, as usual.

Probably will come down to nowcasting.

Yep battle ground further S than the 0Z. This will change many times though, sometimes moving N or S.

Im going to have a little ramp and say that if this battle ground situation occurs then a major snow event would occur with snowfall amounts being around 1ft!

[nick sussex]

Shortwave from the main trough near the eastern USA looks like closing off the high, absolutely wonderful run! I can barely contain my excitement here! these are synoptics if they verify not seen for years.

Edited December 24, 2009 by nick sussex

[cooling climate]

The 06z run seems to be taking the route I mentioned last night with the possibility of the block to

the north running round the eastern flank of the vortex and linking up with the Atlantic ridge giving

more of a n/e airflow which could well turn out to be even colder scenario.

[BLAST FROM THE PAST]

Yep battle ground further S than the 0Z. This will change many times though, sometimes moving N or S.

Im going to have a little ramp and say that if this battle ground situation occurs then a major snow event would occur with snowfall amounts being around 1ft!

I'll raise you by 3 inches

BFTP

[*Stormforce~beka*]

Looking at the charts beyond +144 and you have to ask yourself is this possible? Well the answer is yes although in previous years I would of been dubious. The difference between now and recent years is the state of the AO and also the behaviour of the Polar Vortex so far this winter. Remember if the AO is positive then this indicates lower pressure than normal around the pole which increases strong SW,ly flow and a series of deep LP systems that normally track N of the UK. However if the AO is trending towards being negative then this increases the chances of HP at N,ly lattitudes. Also the PV has been rather pathetic this winter and has failed to become strong or organised. The ECM shows a split PV with part of this being in Scandinavia. Remember in recent years we have seen a strong PV centred over Greenland.

Thank you for this. I have often wondered what all this "technical speak" was on about but to afraid to ask. I'm a dumb one ...

Now it makes a little more sense - Perfect post!

[Wales123098]

Snow storms at the moment for where I live by the look of it, dread to think how were going to react we had 2inches the other night and a futher inch last night and all hell brakes out on the roads lol.

[snowlover2009]

nothing for us up here next week infact you would be looky to get much ppn in the n.midlands all the ppn is to the far south. these sort of scenarios brought a lot of snow for here in the 70s and 80s.

although gfs into middle of the week onwards could give us heaps and heaps

Edited December 24, 2009 by snowlover2009

[TEITS]

Thank you for this. I have often wondered what all this "technical speak" was on about but to afraid to ask. I'm a dumb one ...

Now it makes a little more sense - Perfect post!

No problem and remember never be afraid to ask.

Looking at the model output overall and I have to say I feel sorry for members in Scotland and N England especially the N. At the moment its looking increasingly unlikely that you will see any mild temps and remain in the cold/very cold category. I say feel sorry because to be honest im looking forward to a brief warm up so I can thaw out!

I would also like to add that those who refer to it turning milder next week then remember this. The LP system that moves E will bring milder air into the S, although how far N this mild air goes uncertain. However its this very LP system with the combination of HP near Greenland that brings a return to cold. Also worth remembering that for the UK to have a massive snow event then you need this clash of airmasses. If this model output continues then someone could get large anowfall amounts with higher ground even seeing 40cm. There you go BFTP i've raised you again.

Nearly forgot but tonight thete is the risk of maybe some more snow. An area of precip will move N tonight into the SE/E Anglia as we see LP move NE. The BBC are suggesting that someone on the boundary between the precip and the colder air could see some sleet or snow but at the moment im not convinced!

Edited December 24, 2009 by THE EYE IN THE SKY

[Frosty.]

Yep battle ground further S than the 0Z. This will change many times though, sometimes moving N or S.

Im going to have a little ramp and say that if this battle ground situation occurs then a major snow event would occur with snowfall amounts being around 1ft!

TEITS I thought you were saving your ramping until after christmas dinner

The 6z takes us another step closer to severe wintry spell number 2, greenland/atlantic high link up, strong scandi trough, bitter outbreak of arctic air pushing south as next week progresses with major snowfalls and severe frosts.

[snowlover2009]

No problem and remember never be afraid to ask.

Looking at the model output overall and I have to say I feel sorry for members in Scotland and N England especially the N. At the moment its looking increasingly unlikely that you will see any mild temps and remain in the cold/very cold category. I say feel sorry because to be honest im looking forward to a brief warm up so I can thaw out!

I would also like to add that those who refer to it turning milder next week then remember this. The LP system that moves E will bring milder air into the S, although how far N this mild air goes uncertain. However its this very LP system with the combination of HP near Greenland that brings a return to cold. Also worth remembering that for the UK to have a massive snow event that you need this clash of airmasses. If this model output continues then someone could get large anowfall amounts with higher ground even seeing 40cm. There you go BFTP i've raised you again.

would that system deliver here. because the way i see it,the models are showing it to the south

[TEITS]

would that system deliver here. because the way i see it,the models are showing it to the south

Way too early to tell.

At the moment if the model output continues with the same trend then it could be anything between the N or S Midlands/S Yorks/N Yorks. Even this would change until +24hrs. In these situations its quiet possible that only 30miles is the difference between heavy rain or a blizzard.

I will add though that if the battleground is further S then parts of E Anglia/SE would probably see rain whereas inland locations would see snow. The reason for this is due to the NE,lys spreading across the warmer sea. Something worth considering whilst we ponder on where this battleground will be.

[Cecil Hogmanay Melchett]

WOW.

Thats all i can say really this morning.Ecm looks tremendous,gfs 06z looks very good.Only slight fly in the oitment is ukmo which shows an unfavourable low to the SW which could ruin things if it tracks towards the UK and cuts off any impending Northerly flow.

I never like to write off the ukmo but its looking a bit lonely this morning how it handles events to the SW so fingers crossed it will improve for 12z.

[Costa Del Fal]

Well next Tuesday would be pure WOW if it came off. Here would be in a perfect location to recieve that snowfall weve deserved for ages!

Anyway this will shift North and South over the next few days. Its interesing to see how the cold air floods back after Boxing day. Tuesday could prove a real battleground scenario if it came off. One to watch over the next few days.<_<

[doublebarrel]

Morning all, Merry xmas, Having read these posts and getting a little excited about them our local radio goes and spoils it !! 6C forecast for next week here ! so i`m still ( again ) wondering what charts they look at because the ones on here show different! yet again confused as what to believe ! <_<

[Tom D]

This morning's ECM 00z is quite frankly stunning! The GFS is also pushing towards another cold spell after a breif milder interlude (more so in the south than the north).

The track of the low incoming for early next week needs to be watched - slight movement north or south could change the temperatures and precipitation for the south (the 00z showed ave temps up to 12c with torrential rain for next Tuesday, but the 06z run keeps it further south so temps stay around 5/6c.

It definitely seems another cold spell is on the way, but how long will it be before we start calling this a cold period/winter? December CET looks to be way below the 30yr average, whilst January is also set to be well below average. The cold weather is never really going to leave Scotland for long.

Something else that's got me thinking is whether we're actually seeing a change in our winters (having had 2 hefty snowfalls/cold spells here this year) or whether it's just that this kind of winter set up is getting rarer and we may not see model outputs like this for another 20 years after this winter is over. <_<

[beng]

Way too early to tell.

At the moment if the model output continues with the same trend then it could be anything between the N or S Midlands/S Yorks/N Yorks. Even this would change until +24hrs. In these situations its quiet possible that only 30miles is the difference between heavy rain or a blizzard.

I will add though that if the battleground is further S then parts of E Anglia/SE would probably see rain whereas inland locations would see snow. The reason for this is due to the NE,lys spreading across the warmer sea. Something worth considering whilst we ponder on where this battleground will be.

Actually if you look at the ECM which does have the battleground further South,

http://en.vedur.is/weather/forecasts/atlantic/#teg=temp&type=prec

We end up with almost a direct surface Easterly across the SE - which will mean little chance for modification over the N Sea (given the timing the low level feed will be off an icy continent). The ECM has 850s below zero at midnight Tuesday across the whole of southern England - and they are falling from this point onwards. From a selfish point of view I hope the ECM verifies as it would be something special here - but obviously it may not. It's really a chart of yesteryear so I won't believe it until it's t48.

Ideally I'd like to see decent snow cover across the whole UK (must be a while since this last happened - 81/82?) - which will make the cold very hard to shift given the jet profile. Might have to buy some snow tyres if that happens though!

<_<

Edited December 24, 2009 by beng

[swilliam]

I think what was interesting and slightly different about the last GFS run was that the HP never makes it to Greenland (in terms of an upper blocking high) and meanders around in the vicinity of Iceland e.g.

Despite this there is virtually uninterrupted cold and wintriness once the block is established. This is because of the absence of the PV to our North so we do not have stuff coming round the top of HP introducing Atlantic air again and putting pressure on the block. As someone mentioned previously the PV is nicely positioned to the West of Greenland with another important bit in Scandi.

Our blocking HP is actually linked to the arctic/Siberian HP - almost the reverse of the usual situation. So instead of sinking highs we have rising highs (should that be floating?). Quite an unusual situation I would suggest.