General Model Output Discussion

[Thundery wintry showers]

As others have suggested a rather interesting looking frontal event for Tuesday/Wednesday- widespread snowfalls are suggested and while it does turn milder afterwards, it isn't a snow to rain event as the arrival of milder air occurs a couple of days after the front has passed over.

I doubt it will transpire the way the GFS is currently showing (such events are more often aligned W-E rather than N-S) but worth keeping an eye on.

[Snow storm]

The coldish air holds on till thurs in this run. (amazing considering the GFS yesterday wanted to bring it back for tomorrow ) I am surprised no one has commented on this.

The southerly blast only looks set to last 3 days from the 12z

In FI the GFS is keen to bring the easterly blast back- http://www.wetterzentrale.de/pics/Rtavn2161.png

A much improved run IMO.

[Thundery wintry showers]

I still think there's roughly 60% chance of Britain staying in a no-man's land and 20% of it turning milder from the west. However, the other 20%- the evolution to an easterly which eventually brings cold upper air in- is an evolution strongly reminiscent of late January 1972:

http://www.wetterzentrale.de/archive/ra/1972/Rrea00119720126.gif

http://www.wetterzentrale.de/archive/ra/1972/Rrea00119720127.gif

http://www.wetterzentrale.de/archive/ra/1972/Rrea00119720128.gif

http://www.wetterzentrale.de/archive/ra/1972/Rrea00119720129.gif

Note that during the initial NE'ly blast on the 28th January 1972, there was no particularly cold upper air in the near vicinity (similar to what GFS 12Z shows at around T+168), but over the following three days progressively colder air came across from the east.

[Shiny_Bottom_1]

Not entirely true- the ECMWF showed a similar synoptic evolution this morning, but had sent a colder pool of upper air across from the east, giving us a pretty cold-looking easterly with sunshine & snow showers likely. GFS's version is much more modified and would not give widespread snowfalls. UKMO's T+144 chart also shows a similar trend- the Atlantic looks strong but that low over Britain, when shown on model outputs, has a tendency to be progged to slip SE allowing easterlies in.

Hi Ian.

Sorry. Was talking about events T+36, rather than T+144.

12z's heavier snow, at least from what I read (but down to memory) was not supported this morning - 00z UKMO showing the front decaying.

[Frosty.]

Well the GFS 12z is a nice surprise in FI land, we can't avoid some form of milder incursion between friday and sunday and it does look as though rain will be spreading from the west during friday and then stalling over the spine of the uk during the weekend with gale force southerly winds but temps still in fairly low single digits celsius apart from sw england which looks somewhat milder and a thaw will occur. Hopefully the cold continental air will be pulled back westwards next week but a milder blip is likely.

[pureasthedriven]

The coldish air holds on till thurs in this run. (amazing considering the GFS yesterday wanted to bring it back for tomorrow ) I am surprised no one has commented on this.

The southerly blast only looks set to last 3 days from the 12z

In FI the GFS is keen to bring the easterly blast back- http://www.wetterzentrale.de/pics/Rtavn2161.png

A much improved run IMO.

There's that 1050 scandi/west Russian high lurking again. Keeps popping up around the 20th, has done for a considerable number of runs now, albeit not in precisely the same location (as one would expect).

[Thundery wintry showers]

Hi Ian.

Sorry. Was talking about events T+36, rather than T+144.

12z's heavier snow, at least from what I read (but down to memory) was not supported this morning - 00z UKMO showing the front decaying.

I see now- it's very easy to misinterpret people's posts! In that case I agree.

[ANYWEATHER]

The coldish air holds on till thurs in this run. (amazing considering the GFS yesterday wanted to bring it back for tomorrow ) I am surprised no one has commented on this.

The southerly blast only looks set to last 3 days from the 12z

In FI the GFS is keen to bring the easterly blast back- http://www.wetterzentrale.de/pics/Rtavn2161.png

A much improved run IMO.

Totally agree!If you have a look at the gfs temps you will see that double figures are only reached in the far south for about 24hrs at the weekend! That block to our East is huge and it wants to pay us another visit!!

[Polar Continental]

Hi Nick,

Yes GFS still showing,shall i say,a less cold trend by the weekend but the development of that shortwave over England midweek complicates things and shows some resistence from the cold air ahead of the front.

This mornings ECM ext ens showed a more colder runs further out indicating that the block to the East is sticking around.

What we don`t want is the Atlantic trough seting up just to our West like in Nov.which would leave the uk under the influence of the Atlantic.

Some attempts at undercutting are still being shown on this run but it doesn`t quite complete the job in the nearterm on this run.

http://www.wetterzentrale.de/pics/Rtavn1441.png

Just to much strenth in the piece of vortex to our NW.

Meanwhile there could be quite a bit of snow Tues/Weds for some areas,particularly Wales and much of the Midlands

http://www.wetterzentrale.de/pics/Rtavn484.png

http://www.wetterzentrale.de/pics/Rtavn4817.png

http://www.wetterzentrale.de/pics/Rtavn4810.png

http://www.wetterzentrale.de/pics/Rtavn482.png

On this run we have the percip.low temps and dewpoints as the front approaches.

Probably snow for parts of the South West too,although more chance of this turning to rain eventually.

Hi Phil,

Good summary there, I have just updated my web-site, very much agrees with what you are saying.

The difficulty the models are having as to how far north the precipitation gets through Tuesday and in to Wednesday, the potential for heavy snow over wide areas of inland southern counties is increasing and for the midlands too as you say.

My thoughts for the weekend are for much less cold conditions getting a much better grip. The GFS shows the source of the southerly flow from much further south and with some Atlantic influence this time also.

http://www.wetterzentrale.de/pics/Rtavn1081.png

The question is how long?

[Snowyowl9]

Is that as mild as it gets 3 or 4c about as high as the period after christmas then.

http://www.wzkarten3.de/pics/Rtavn1261.png

http://www.wzkarten3.de/pics/Rtavn12617.png

That won`t thaw much snow.

Edited January 11, 2010 by Snowyowl9

[SP1986]

3-4C will be more than enough to quickly melt any snow.

At the end of the cold spell last it was a similar scenario, hanging around in a featureless weather pattern, which only slowly got milder. I would put more money on milder weather returning that colder, but that's only based on the past not current. We'll see.

[snowingtequila]

Is that as mild as it gets 3 or 4cabout as high as the period after christmas then.

http://www.wzkarten3.de/pics/Rtavn1261.png

http://www.wzkarten3.de/pics/Rtavn12617.png

That won`t thaw much.

it will be washed away with the rain though. I think all the models are now starting to edge towards a possible reload of the easterly or staying on the edge of it like we are now, dull, cold etc. The only thing that concerns me and thinks the atlantic may push the block further away or the high pressure sink SE is the positioning of the polar vortex which seems to be setting up over Greenland, maybe someone could confirm this and say how important this it.

[Snowyowl9]

3-4C will be more than enough to quickly melt any snow.

At the end of the cold spell last it was a similar scenario, hanging around in a featureless weather pattern, which only slowly got milder. I would put more money on milder weather returning that colder, but that's only based on the past not current. We'll see.

Not here it won`t not the amount thats here and more to come yet, still got snow from before christmas which didn`t all thaw.

And it`s a SE-ly wind with dryer air,there is alot of wind though which may thaw quicker.

[Methuselah]

3-4C will be more than enough to quickly melt any snow.

At the end of the cold spell last it was a similar scenario, hanging around in a featureless weather pattern, which only slowly got milder. I would put more money on milder weather returning that colder, but that's only based on the past not current. We'll see.

I pretty-much agree with that, Ste. A gale at 5C will melt snow quite quickly, methinks? Still air wouldn't; but, if the GFS is anything to go by, we'll not be in still air??? There's plenty of time for change yet, though...

[MR EXTREMES]

Totally agree!If you have a look at the gfs temps you will see that double figures are only reached in the far south for about 24hrs at the weekend! That block to our East is huge and it wants to pay us another visit!!

that is one hell of a southerly on that chart going into the arctic look where it comes from north africa cant see that being to cool.

[snow1975]

it will be washed away with the rain though. I think all the models are now starting to edge towards a possible reload of the easterly or staying on the edge of it like we are now, dull, cold etc. The only thing that concerns me and thinks the atlantic may push the block further away or the high pressure sink SE is the positioning of the polar vortex which seems to be setting up over Greenland, maybe someone could confirm this and say how important this it.

I agree. The PV is developing over the POle. Is the AO going positive?

There are hints of a SSW event soon, that could eventually disrupt the PV across the Pole and give us an easterly in February again???

[SP1986]

Well 1C has certainly got rid of the snow that was on the ground here (almost), and has got rid of an inch or so overnight so it can shift although I do acknowledge as Pete has said the wind has played a factor. I think these also other factors in melt which include the dewpoint. As far as I recollect, a dewpoint over 0C will aid snow melt, whereas a dewpoint under 0C will help preserve it/slow down the melt.

[Snowyowl9]

Well 1C has certainly got rid of the snow that was on the ground here (almost), and has got rid of an inch or so overnight so it can shift although I do acknowledge as Pete has said the wind has played a factor. I think these also other factors in melt which include the dewpoint. As far as I recollect, a dewpoint over 0C will aid snow melt, whereas a dewpoint under 0C will help preserve it/slow down the melt.

No melt here at all at 0.4c snow is still dry.

Think the hills and scotland N england there will be snow lasting all winter in some form theres an awful lot to thaw.

[Methuselah]

Well 1C has certainly got rid of the snow that was on the ground here (almost), and has got rid of an inch or so overnight so it can shift although I do acknowledge as Pete has said the wind has played a factor. I think these also other factors in melt which include the dewpoint. As far as I recollect, a dewpoint over 0C will aid snow melt, whereas a dewpoint under 0C will help preserve it/slow down the melt.

I think that you're right enough Ste, re: dew point...And, if what the GFS is showing comes to be, snow will melt quite quickly, I think. But, as I said before, I'd rather see this lot go now, than see a catastrophic melt occur in March!

[phil nw.]

Hi Phil,

Good summary there, I have just updated my web-site, very much agrees with what you are saying.

The difficulty the models are having as to how far north the precipitation gets through Tuesday and in to Wednesday, the potential for heavy snow over wide areas of inland southern counties is increasing and for the midlands too as you say.

My thoughts for the weekend are for much less cold conditions getting a much better grip. The GFS shows the source of the southerly flow from much further south and with some Atlantic influence this time also.

http://www.wetterzen...s/Rtavn1081.png

The question is how long?

Thanks Paul.

It`s still a developing situation as the hrs. tick by .

As you suggest doubts will remain wrt amount and spread of the snow but the aformentioned regions seem to be favourites.

Further out looks slightly milder for at least a short period but that Scandi block is still lurking.

Edited January 11, 2010 by phil n.warks.

[nick sussex]

The ecm is now showing good consistency in the pattern upto 168hrs. And this trend is now being picked up by the rest of the models. The huge block extends a ridge westwards by 168hrs and the Atlantic trough looks favourably aligned here, in most recent winters it has been the cold snaps interspersed with long milder interludes or just mild! could this be the winter of the blink and you'll miss them milder snaps! Still waiting for the rest of the ecm to come out but so far very encouraging. At 192hrs the cold is well and truly back, if the Atlantic trough disrupts at this point and sends a shortwave under the block then time to get the woolie hat and ear muffs out once again!

Edited January 11, 2010 by nick sussex

[cooling climate]

Just seen your post Nick. I was going to say the ECM t192 chart should certainly cause a stir.

T216 is fantastic, game on.

Edited January 11, 2010 by cooling climate

[nick sussex]

Just seen your post Nick. I was going to say the ECM t192 chart should certainly cause a stir.

At 216hrs it's almost there, if the energy cuts under the block here comes big freeze part 3! Of course there is along way to go and its a complicated set up. The crucial part of the run comes at 144hrs to 168hrs, so still too far out to be sure but at least the trend is there. The ecm ensembles should hold alot of interest this evening!

Edited January 11, 2010 by nick sussex

[Tom D]

ECM is amazing! The block spreads right over to Greenland by +216, a truly monster high pressure!

Not sure what others think of the transition between +192 and +216, a little OTT with the high expansion?

[Eugene]

then time to get the woolie hat and ear muffs out once again!

[

Still need them for most of this week maybe give them a break for a day or two at the weekend then back out again, poor things have to buy some new ones soon they are getting worn out from all the use this winter

Ps excellent ECM 12Z