Model Discussion - January 17th

[damianslaw]

Very quiet in this thread tonight - too be expected given what may appear to be poor offering from the models today for those looking for cold and snow. However, the upstream hemispheric pattern is suggesting a shift to a much more blocked set up as we approach February and thus a much weakened PV which is the key to any long term sustained cold.

Encouraging to see the Met office suggesting a much colder period could be on the cards as we head into next month - the met is notoriously careful with what it says, and it is the first time they have intimated at such potential, will be interesting to see whether they firm up on the likely pattern soon or remain sat on the fence until nearer timescales appear - but something must be happening for them to state this and it supports many of those upstream signals.

Back to the here and now- all models showing a very similiar outlook to what we endured during the first half of December, though low pressure will be much less intense and the warm/cold sectors less pronounced, still northern parts with height especially Scotland should see the return of the white stuff from Thursday after a month of absence - the last month has been shockingly poor on the snowfall front even on the highest ground in the Highlands - afetr such a promising start to the winter season I suspect the ski resorts are crying out for some snow and those cool/cold zonality conditions again - it looks like there prayers are about to be answered - any mild sectors for the foreseeable future look weak quick affairs especially in the north - so hopefully the hills will retain there snow cover with freeze/thaw action at times.

[BLAST FROM THE PAST]

Thanks Phil and Cloud 10. GP is that anomaly chart what you envisaged?

BFTP

[LomondSnowstorm]

Tonight's 8-14 anomaly illustrates both the potential and the potential pitfalls that lie between us and a major cold spell. As Stewart predicted, positive height anomalies are now appearing over Greenland but unfortunately the centre of the greatest mean heights lies to the west of Greenland. Heights still present all the way across to Novaya Zemlya, but the pattern ideally needs to shift southwards/eastwards for the UK to see any real benefit from it.

[BLAST FROM THE PAST]

L

Bearing in mind its moving towards that and may just be the beginning of it all. Date 25th with trouh over UK, looks on the mark to me and its where it moves from there

BFTP

[patrickshere]

Is that a shortwave I see off of the main low?

Be interesting to see if it becomes a feature at all in this run..

[Jason M]

Big differences even at 72 hours in the way the low pressure is behaving near Iceland. Looks a little better to me (lol, maybe not).

Jason

Edited January 17, 2012 by Jason M

[Earth Wind and Snow]

Yuk!!!

For newbies a western based negative NAO often comes about when you have higher latitude blocking but its core sets up too far west and you're on the mild side of any troughing, an eastern based often delivers cold east to ne flows as any troughing is often over Scandi or further east and you're on the cold side of the trough.

I have to talk about the UKMO further outlook here as its relevant to that so apologies mods but I can't explain it any other way!

I sense the reason for the uncertainty in that outlook is that theres a good signal for higher latitude blocking, the reason they're giving these two options with no real middle ground is that this is really the only type of set up where you can have such a marked difference in weather.

I suspect theres a big split in the ECM longer range ensembles and thats why they've given that type of outlook, blocking yes but where and that will probably decide the rest of the winter.

You could be very much on the right track Nick - 1956 springs to mind

http://www.wetterzentrale.de/pics/archive/ra/1956/Rrea00119560112.gif

However it could also be that the UK MET foresee a 'Kettley High' type scenario playing out. High pressure building to our north-east that may or may not influence our weather.

Could be a near miss like in 2001 - bitter cold to the north-east but we stay on the mild side

http://www.wetterzentrale.de/pics/archive/ra/2001/Rrea00120010201.gif

http://www.wetterzentrale.de/pics/archive/ra/2001/Rrea00120010204.gif

Or 2007 - close but no cigar - this one gave a lot of us nightmares in the lead up to that spell as some of the models were plunging us in to a major freeze before a late backtrack

http://www.wetterzentrale.de/pics/archive/ra/2007/Rrea00120070221.gif

http://www.wetterzentrale.de/pics/archive/ra/2007/Rrea00120070223.gif

Or Perhaps they see a chance of a direct hit like the famous 1987 spell

http://www.wetterzentrale.de/pics/archive/ra/1987/Rrea00119870110.gif

http://www.wetterzentrale.de/pics/archive/ra/1987/Rrea00119870112.gif

Either way I expect some tasty charts to start appearing over the next few days - we just have to hope that our luck is in and we hit the jackpot

ECM even at T120 has all sorts of possibilities so anything can happen especially the way the charts have been flipping over the last two weeks

http://www.wetterzentrale.de/pics/Recm1201.gif

EWS

[Cal]

Tonight's 8-14 anomaly illustrates both the potential and the potential pitfalls that lie between us and a major cold spell. As Stewart predicted, positive height anomalies are now appearing over Greenland but unfortunately the centre of the greatest mean heights lies to the west of Greenland. Heights still present all the way across to Novaya Zemlya, but the pattern ideally needs to shift southwards/eastwards for the UK to see any real benefit from it.

If the chart were to verify, then possibly the higher risk of slider lows coming into force over the uk transfering the energy south & south east wards.

[bluearmy]

obviously, everyone is busy searching for support for exeter's update.

a few interesting snippets

ecm mean at day 10 shows an small upper ridge just west of iceland. it wont take much blocking in that area to send the depressions on a more southerly track.

naefs at day 10 not in agreement with that little feature and dropping a bit more energy off the distorted vortex into the greenland area.

both models have thicknesses in southern england around mid 530 dam.

tbh, running the frames, the general trend for heights to lift out our side of the NH but without any definite trend to place the blocking (apart from eastern canada and nw siberia).

the anomoly chart from naefs at the end of the month shows the potential

finally the clustering of higher heights at the end of the run shows a nicely positioned block.

[LomondSnowstorm]

L

Bearing in mind its moving towards that and may just be the beginning of it all. Date 25th with trouh over UK, looks on the mark to me and its where it moves from there

BFTP

That's very true, I didn't mean to say that this was set in stone by any means, or that this was a negative chart for cold prospects- it certainly isn't. That trough could so so easily move southeastwards or even eastwards by the end of the month leaving us in a very favourable position for cold. Height anomalies are certainly low to the south on that which would be another helpful piece to the puzzle. We appear to be moving towards a longer term solution tonight - whether that will be favourable for us or not remains to be seen for the moment.

[Tim Bland]

Everything further south with -4 uppers widely on Monday on the 18z. Better heights over Greenland as well.

[PolarWarsaw]

-5 quite widely shown by Tuesday as well. Better run so far.

[Cheshire Freeze]

Yes a better run at 168 this......trough dropping over the UK with some low thicknesses......

[Matty M]

Looks like a segment of the PV is going to try and move to Scandy progressively. After time this will enable a good cold spell to develop

I think we are definitely moving forward to a position where we will have a good go at a prolonged cold spell in early very late Jan early Feb

Edited January 17, 2012 by Matty M

[Snowy Easterly]

At T168 the pressure is 1040mb over a part of greenland but why is it still blue on the chart ?

[PolarWarsaw]

-5 uppers into northern france by next wednesday morning.

[Cloud 10]

Less amplification of the jet on the 18z,resulting in the comments above.

12z> 18z>

[nick sussex]

Thanks EWS for putting those charts up. It clearly shows how you need some luck to get the blocking in the right place.

[dixonoid]

At T168 the pressure is 1040mb over a part of greenland but why is it still blue on the chart ?

If it links with high pressure further south, it should start dragging warmer air north. firming the grip of the block.

[J10]

At T168 the pressure is 1040mb over a part of greenland but why is it still blue on the chart ?

the 1040mb is the Surface High Pressure, the blues over Greenland indicate there is no high pressure at the higher latitudes, still it is better than purple over Greenland, definite signs of a weakening Polar Vortex.

[feb1991blizzard]

At T168 the pressure is 1040mb over a part of greenland but why is it still blue on the chart ?

Its light blue though so at least its getting there, sometimes surface pressure doesnt directly link to geopotential heights, this very common over greenland, ideally we want to see green or even yellow colours to the NW of us.

[mountain shadow]

At T168 the pressure is 1040mb over a part of greenland but why is it still blue on the chart ?

That is the surface pressure and aint good enough. You want to see oranges and reds signifying height rises at 40,000 feetish where the jetstream is. It is that which blocks the jet.

Whilst the 18z brought a wee northerly, it will not last unless we get proper upper height rises into Greenland. I feel like that is all I'm posting at the moment.

[Tim Bland]

Snow on the south coast on Weds! Massive upgrade in the relative short term! Could be a cold outlier though?!

[Snowy Easterly]

Thanks for the replies

GFS FI returns to the usual default mode though

[Jason M]

Ignore the low res! Notice how after 192 we suddenly get lots of dartboard lows and pressure drops like a stone over Greenland.

Ok(ish) run, but the wait goes on despite the bizarre meto update today.

Jason

By the end our old friend is back.

http://www.meteociel.fr/modeles/gfse_cartes.php?&ech=348&mode=0

A Bartlett is for life not just Christmas . Joking aside though, the latter stages can go in the bin IMO.

Edited January 17, 2012 by Jason M