Winter Model Discussion - Cold Hunting - 20th Dec

[chris55]

Fantastic post and sums up pefectly well what the SSW events are all about. Just another small piece of the puzzle for cold in UK, NOT the holy grail.

From a personal perspective, I'm not going to bother so much about this SSW which is progged. I recall similar excitement and expectation being lashed around one which I believe occured last winter, and the net result - for the UK at least - wasn't anything extraordinary at all. I understand the science, but I'm not so confident many others do. All I see from SSWs, is an adjusted boundary threshold which lends itself more conducive to blocking in the NH. However, that doesn't guarantee diddly squat to the British Isles on a local level.

I really would urge extreme caution with this SSW; let's see whether it actually produces anything of note for the UK, before pinning any hopes on that donkey. We can, at least, see the event itself manifesting within the models - and this has been a solid signal - but we really need to wait, and see what effect this really has.

It's all about probabilities when looking at the mid term weather prospects, and a SSW increases the probability of something colder. It doesn't guarantee anything by any means, and I hope no one would be pinning anything anywhere based on computer models or SSWs at range.

We just need to sit back and see what transpires WRT the Start and what affect it may have on our part of the world..

Edited December 22, 2012 by chris55

[Frosty.]

The Gfs 12z op run is quite funny as it finds every conceivable way of not bringing cold weather to the uk, so whilst it's pathetic on one level, it's amusing on another. The Ecm 12z is marginally better but synoptically it's in the embryonic stages of developing something which may subsequently grow into something more promising from a cold perspective, but the gfs 12z is ghastly and I want the 6z back already.

[Zakos]

Not too shabby

It may be 216 hours away, but the upgrade that produces this cold shot appears much earlier on.

At 144 hours, we can see the low near Iceland is further south. I believe this is a direct result of stronger pressure over the Arctic

The Arctic high is larger and stronger on the ECM. IMO this forces the jet stream and thus the depressions to take a more southerly track.

Much better ridging in the Atlantic, possibly also due to the stronger Arctic highs.

I would agree with those that say unsettled conditions will be prevalent across the UK for the next 10 days or so.This does not mean that we cant see significant cold or snow, it simply means the cold will be unlikely to be prolonged.

The Bigger picture is the same here on both the ECM and GFS.The difference is the position of the jet stream. Unfortunately this seems to be changing alsmost every run, and we are unlikely to know for sure until 72 hours or so from the event.

[Weather Boy]

From a personal perspective, I'm not going to bother so much about this SSW which is progged. I recall similar excitement and expectation being lashed around one which I believe occured last winter, and the net result - for the UK at least - wasn't anything extraordinary at all. I understand the science, but I'm not so confident many others do. All I see from SSWs, is an adjusted boundary threshold which lends itself more conducive to blocking in the NH. However, that doesn't guarantee diddly squat to the British Isles on a local level.

I really would urge extreme caution with this SSW; let's see whether it actually produces anything of note for the UK, before pinning any hopes on that donkey. We can, at least, see the event itself manifesting within the models - and this has been a solid signal - but we really need to wait, and see what effect this really has.

Whilst I agree with your sentiments here (and i enjoy your posts generally btw)I think that your comment about last winter is factually inaccurate because I think that the strat event that you refer to did indeed give rise to a significant cold spell in early February - in fact the only one of the winter. So I think that experience lends support to the strat theory.

However you are right that strat warming seems to lead to increased blocking and it does not follow that we will get cold weather although of course it makes it more likely.

Im pretty sure that I'm one of the ones that doesn't understand the science other than very broad concepts. Perhaps Chio or yourself could help us one day, although it's worth bearing in mind that this board has sceptics of the strat effect - TEITS for example.

[Frosty.]

This may sound utterly crazy but I still think the models are struggling from boxing day onwards. This obviously has a domino effect for the rest of the run, so I think the 00z tomorrow will be our last chance saloon as far as a brief wintry burst on the 26th/27th is concerned.

[Gibby]

Good evening folks. Here is the report on the 12z output from GFS, UKMO and ECM for this evening Saturday December 22nd 2012.

All models show a mild and very wet SW flow over the UK which gives ground a little over Central areas for a time tomorrow leaving the risk of rain still for Southern England tomorrow and in the North where it will be rather colder, notably so in the far NE and Northern Isles who will see storm force SE winds and spells of rain, sleet or snow throughout the next 24 hours. rain is shown to return NE later tomorrow as a wave runs NE on todays' front. This will bring further rain and flooding problems to the SW tomorrow night in a strong and gusty SW wind. On Christmas Eve many areas see a brief respite from the wind and rain though a new trough will bring rain in from the West late in the day. The front moves on East though quite quickly Christmas Eve night with the two main days of Christmas seeing a fresher and rather colder couple of days with sunshine and showers, wintry on Northern hills.

GFS then shows the brief colder and showery NW flow displaced after the holiday with a milder SW flow again with some rain, this time heaviest in the North and West. This mobile zonal flow continues then with rain at times in a Westerly wind, strong at times with temperatures well up for late December. In FI tonight the operational shows no real change with a broad and mild and strong West or SW flow with rain at times, chiefly in the North and West with some longer drier spells in the sheltered East where it would no doubt become very mild at times in any brighter spells.

The GFS Ensembles show a continuation of mild and windy Atlantic winds flooding the UK with bands of rain throughout with the driest weather likely in Easternmost areas in the lee of high ground to the West.

The Jet Stream shows an unrelenting train of upper winds moving West to East undulating north then South in a sine wave pattern in the latitude of the British Isles for the next week or so.

UKMO for midday on Friday shows a strong and mild SW flow in association with a very deep depression in mid Atlantic driving bands of rain NE over the UK.

ECM shows a similar pattern towards the end of next week and weekend but as the New Year arrives a change to drier, brighter, colder and more frosty conditions look possible as a large High forms over the Southern half of the UK.

In Summary the weather remains in volatile mood between now and the New year with periods of rain and strong winds in relatively mild conditions, apart from a few slightly colder days over Christmas itself. The Environment Agencies will no doubt remain very busy over the period with further flooding issues nationwide at various times in the next few weeks, notably in the SW over the coming days and maybe Northern areas later. They will be hanging their prayers on the operational of ECM coming to fruition when a welcome break in the weather is shown by New Years Day.

[Froze were the Days]

168-192z on the ECM doesn't look right to me, it 'flattens' the LP whilst sliding ESE although there are no height rises to the north and yet again another short wave appears near to Iceland/Norwegian Sea (doesn't surprise me), but the idea of a lull in the wet conditions with height rises close to the UK I can agree on in about a weeks + time.

[Gavin Hannah]

I've concluded that the models throw in shortwaves when they get stuck, just so they have something to work with....

Up to and including boxing day looks pretty straight forward, it's what happens there after that intrigues.

[nick sussex]

Well at least the ECM delivers a little interest with a chance to develop something a bit more wintry for the UK.

Its output is plausible given the expected changes upstream in the USA, although it doesn't quite deliver at the end it at least shows whats possible with a positive PNA.

Its movement of the main PV towards northern Canada also ties in with yesterdays discussion at NOAA.

Will be interesting to see whether the ECM ensembles support this trend when they come out soon.

Edited December 22, 2012 by nick sussex

[JP1972]

This may sound utterly crazy but I still think the models are struggling from boxing day onwards. This obviously has a domino effect for the rest of the run, so I think the 00z tomorrow will be our last chance saloon as far as a brief wintry burst on the 26th/27th is concerned.

With all due respect Frosty (and your posts are one's which I look out for when browsing this forum), I think you and many others are clutching at straws.

And as others have alluded to, this Strat Warming event may not have any effect (wintry wise) on Britain whatsoever at all.

I think it's best just to accept (for the forseeable) that anything remotely wintry is likely to be localised and on high ground, whether we like it or not. It's perhaps best to take the models at face value until something wintry appears and consolidates inside T96, fingers burnt and all that quite recently!

[cooling climate]

Quite a promising run from the ECM tonight and although the high topples at

t240 the Arctic high is ridging down so pressure would start to build north

again.

I think it will definitely be a case of look east again as we go into the new

year but with much greater dividens for us this time around.

[swfc]

With all due respect Frosty (and your posts are one's which I look out for when browsing this forum), I think you and many others are clutching at straws.

And as others have alluded to, this Strat Warming event may not have any effect (wintry wise) on Britain whatsoever at all.

I think it's best just to accept (for the forseeable) that anything remotely wintry is likely to be localised and on high ground, whether we like it or not. It's perhaps best to take the models at face value until something wintry appears and consolidates inside T96, fingers burnt and all that quite recently!

Good post and hits the nail firmly on the head

[UV-RAY]

With all due respect Frosty (and your posts are one's which I look out for when browsing this forum), I think you and many others are clutching at straws.

And as others have alluded to, this Strat Warming event may not have any effect (wintry wise) on Britain whatsoever at all.

I think it's best just to accept (for the forseeable) that anything remotely wintry is likely to be localised and on high ground, whether we like it or not. It's perhaps best to take the models at face value until something wintry appears and consolidates inside T96, fingers burnt and all that quite recently!

I think Frosty shares the same sentiments as yourself really, we are all clutching at straws with SSW and other teleconnections that don't always mean cold for these shores.

[No Balls Like Snow Balls]

This is automated over the weekend with no human input however it could be a sign of change to a more blocked Atlantic with a ridge being thrown up towards Greenland - has been shown in some model op runs to. This is the first run where any of the 500mb anomalies have shown this so it can't be taken as gospel just yet.

Edited December 22, 2012 by No balls like Snow Balls

[cerneman]

With all due respect Frosty (and your posts are one's which I look out for when browsing this forum), I think you and many others are clutching at straws.

And as others have alluded to, this Strat Warming event may not have any effect (wintry wise) on Britain whatsoever at all.

I think it's best just to accept (for the forseeable) that anything remotely wintry is likely to be localised and on high ground, whether we like it or not. It's perhaps best to take the models at face value until something wintry appears and consolidates inside T96, fingers burnt and all that quite recently!

Can I please ask that with out any Strat Warning, would we have any prospects of possible cold? Genuine question

[nick sussex]

Looking at the ECM ensembles for De Bilt the operational output is close to the coldest solution on days 9 and 10.

http://www.knmi.nl/exp/pluim/Data/PLUIM_06260_NWT.png

[Bobby]

Yes the ECM mean doesn't show much of a mid-Atlantic ridge

+192

Probably won't be til well into January before we see a change from unsettled conditions looking at everything.

[bluearmy]

This is automated over the weekend with no human input however it could be a sign of change to a more blocked Atlantic with a ridge being thrown up towards Greenland - has been shown in some model op runs to. This is the first run where any of the 500mb anomalies have shown this so it can't be taken as gospel just yet.

yes it looks just like the 00z naefs run did (cos thats what it is!). having looked at the 12z gefs mean, i rather doubt the 12z naefs will look nearly as good.

[Robbie Garrett]

NCEP 500mb anomaly goes well for a decent arctic high @ 240 hours. Looking fairly blocked, but the Azores needs to shift to allow low pressure sink south.

Models still painting an evolution for fruition as we approach the New Year. Notice the low pressure digging south over the Azores High.

NCEP wants to push high pressure further west and connect the Canadian High with the Azores.

Edit - someones just posted something similar to the above chart.

Edited December 22, 2012 by Robbie Garrett

[bluearmy]

Can I please ask that with out any Strat Warning, would we have any prospects of possible cold? Genuine question

GP posted that the telecons support a colder outlook for jan in any case but without the current strat forecast, i would be very cautious looking ahead into jan re cold.

[cerneman]

GP posted that the telecons support a colder outlook for jan in any case but without the current strat forecast, i would be very cautious looking ahead into jan re cold.

Thanks, not worried about any cold for January yet,more interested get the rain gone, But for learning, interested to know significance of any forecast Strat Edited December 22, 2012 by cerneman

[Timmytour]

SSW may be providing us with reasons for optimism, but do I recall correctly that the same signs indicated that the cold spell we had in first few days of February 2009 was set to get more severe into the second half?.

Certainly what actually happened was that it became increasingly mild and almost springlike

[Chris K]

Thanks, not worried about any cold for January yet,more interested get the rain gone, But for learning, interested to know significance of any forecast Strat

If you haven't been pointed to it already - the stratosphere temperature watch thread explains nicely on how warming/cooling can affect us.

[Methuselah]

I thought that SSW events merely serve to enhance the likelihood of Northern blocking? But, since when did NB ever guarantee a BFTE for the UK?

[bobbydog]

any similarities?.....