Winter Model Discussion - Cold Hunting - 20th Dec

[BLAST FROM THE PAST]

Lol! I tend to agree with you there.

Historically PV to the north models overestimate southwards extent of jet and then take this north which they began to do till today where its back south again!

Of course we don't have the uniform PV to the north with this split which does add a different aspect to things.

That is a key element I think.

Ok folks, been an interesting model day today but need some kip, will have one more tomorrow then I'll be internet free for Xmas!!!!! Oh my God......nothing from 23-27 as going to mother-in-law in Norfolk.

BFTP.

Edited December 21, 2012 by BLAST FROM THE PAST

[Zakos]

Actually I was wrong, this is a significant shift of the pattern.

The cold is far closer to the UK on this run.

The Greenland High is stronger and much further south, extending over Iceland. This forces the depressions to take a much more southerly path.

The cold stays constantly in Northern Scotland. If we get one more upgrade like this, it could result in a significant cold spell

[legritter]

Active weather a plenty over next 10 days .the possibility of cold air at 850 mb and plenty of frontal action and troughs getting in on the act .going by tonights runs could be some wintry ness even down to fairly low levels ,not saying snow fest but certainly for some in favoured locations its still a possibility .back to the rain and the monsoon carries on thanks to a train of low pressure systems still heading in our direction off the atlantic .but when will all this change,there are signs but nothing concrete unless iv missed some of the posts ,But certainly not boring .next week after tuesday interesting for some of our northern posters .next lot of rain just slamming into my front room windows as i type ,cheers .

[johnholmes]

a quick summary tonight for the weekly look at what the 500mb anomaly charts suggest for the next 6-15 days.

7-weekly look on fri 21 dec 12.pdf

[Frosty.]

You would like to think that this Northerly would be nailed for Boxing day at this range, after all the current mild muck it would be something to look forward to after the 13c mush tomorrow. I still think there is enough time for more potent cold shot next week just after xmas day.

[Tim Bland]

Best FI chart I've seen fow a while

http://www.meteociel.fr/modeles/gfse_cartes.php?ech=384&code=code&mode=0&mode3h=0&runpara=0&carte=1

[Theresnoway]

I have a couple of learning questions...

Just read the netweather ensemble guide and it talks about spreads, are these the same as anomalies?

The guide is talking specifically about the GFS, do the other models run ensemble data? If so are the data graphs and postage stamps viewable?

Tks

[Grimsby Snow Lover]

Did anyone order an easterly??? Granted this is a million miles away with less than 1% chance of verifying. On a positive note this is the second run that builds hights in the Atlantic during the beginning of January. A new trend??

http://www.wetterzentrale.de/pics/Rtavn3841.png

[If Wishes made Weather]

Looking into far FI over the past couple of days, there seems to be a signal for increased frequency of colder shots of weather within a not dissimilar pattern of a west to east flow breaking to a more northerly flow at times. Higher pressure - albeit in the lower atmosphere - also being progged for Greenland. The last slide of the 18z brings in heights to our north and lower pressure to our south with a slack easterly flow. Of course that way lies madness, and tomorrow that will be gone, but the general trend seems encouraging.

[nick sussex]

Still a large strat warming forecast at the 10hPa level.

This actually starts in the higher resolution output which is good to see. Overall for fear of jinxing things I do feel we are seeing a few green shoots here which hopefully will be covered by snow in January!

We'll just have to hope those comments tonight by NOAA hold true and we get a little help from the strat warming as we move into January.

[Frosty.]

Yes please I will BANK that right now

chief met office forecaster can't believe his eyes.

Edited December 21, 2012 by Frosty039

[nick sussex]

Tonights UKMO fax charts:

96hrs Xmas Day

Occlusion heading se, a chance of some wintry showers into N/Ireland/ N/England and Scotland later on, I think snow though probably reserved for higher ground.

120hrs Boxing Day

Next low moving in from the west but quite southerly tracking, the UKMO 144hrs raw output took this east with Scotland on the colder northern flank of this!

The detail does seem to be changing alot which means those fax charts may well change.

[Theresnoway]

Still a large strat warming forecast at the 10hPa level.

This actually starts in the higher resolution output which is good to see. Overall for fear of jinxing things I do feel we are seeing a few green shoots here which hopefully will be covered by snow in January!

We'll just have to hope those comments tonight by NOAA hold true and we get a little help from the strat warming as we move into January.

Nick,

Am I right in thinking the lower the HPA, the higher up we are talking about?

Is 850hpa (for example) always the same height? Or is that dictated by pressure patterns?

Tks in advance

Edited December 21, 2012 by Theresnoway

[liam79]

Yes please I will BANK that right now

chief met office forecaster can't believe his eyes.

And the fairly long lived northerly before hand, good FI run not that it will turn out like that

[Panayiotis]

Nick,

Am I right in thinking the lower the HPA, the higher up we are talking about?

Is 850hpa (for example) always the same height? Or is that dictated by pressure patterns?

Tks in advance

Yes the lower the hPa, the higher the altitude eg.10hPa is within the stratosphere(higher than the troposphere). Also 850hPa is around 1500m, here is a nice understandable site that i find useful. http://www.blackheat...om/heights.html Edited December 21, 2012 by Panayiotis

[cooling climate]

The 18z must of read the NOAA update with much better ridging off the west coast

of north America.Another run and again the trend for better heights to the north

which of course would tend to deflect the jet on a more southerly course.

Should be a fun during the Christmas holidays watching this trend continue and

develope.

Would not be surprised to find the near miss with the beast from the east this

month was a warning of things to come during the two coldest winter months ahead.

[Tom Montalbano]

For a few runs now GFS has started to develop some signs of blocking to our NW, N or NE, into the first few days of January, still a long way off of course. I've been looking at the Stratospheric Temp charts at 30hpa during these GFS runs, during the earlier part of the run the Strat PV at 30hpa stretches from N.Russia and directly towards the UK and the weather remains very mobile and Atlantic driven but when we hit the first few days of Jan., the PV starts to back away from the UK and becomes stretched again but this time from Russia to Canada, its at this time we start to see heights rise towards our north. This has happened on quite a few GFS runs in the last 3 days or so.

As i mentioned yesterday some of the synoptic evolutions, at that stage on these runs, have looked very similar to whats occurred around a week or so before some of our notable cold spells and very much ties in with GPs thoughts further on into January.

Very interesting model watching at the moment and lets hope these trends continue.

Regards,

Tom.

[PubliusEnigma]

Actually I was wrong, this is a significant shift of the pattern.

The cold is far closer to the UK on this run.

The Greenland High is stronger and much further south, extending over Iceland. This forces the depressions to take a much more southerly path.

The cold stays constantly in Northern Scotland. If we get one more upgrade like this, it could result in a significant cold spell

Compare the charts.. Have a look at the pressure over Greenland, in the charts you've posted compared to this one..

And then this.. What we need to see to call it a pattern change is HIGH pressure building over Greenland, not the low pressure

the models are currently showing ( with embedded surface highs..)

This is what a shattered or absent PV looks like on a chart..

The Greenland high is propped up or supported by the Scandi High, not the other way round. The GH buffers the jet south, and

if a cut off low develops over Sardinia and Corsica, then the you are 'locked' in to cold. There is nothing remotely like this even

out in la la land. Its our Summer Friend, the Greenland High which is the missing piece in the jigsaw, and there only vague signs

of anything remotely similar are out beyond T360 on this evenings 18z.

Edited December 21, 2012 by PubliusEnigma

[mulzy]

The hunt for cold reaches desperation as I have to show a CFS 300 hrs chart (albeit a superb one and maybe not too far fetched!)

Edited December 21, 2012 by mulzy

[nick sussex]

Nick,

Am I right in thinking the lower the HPA, the higher up we are talking about?

Is 850hpa (for example) always the same height? Or is that dictated by pressure patterns?

Tks in advance

Yes thats right the lower hPa the higher up in the atmosphere, for a SSW we need a reversal in zonal winds at the 10hPa level.

So it was good to see the warming still forecast on the GFS 18hrs run.

[johnholmes]

Nick,

Am I right in thinking the lower the HPA, the higher up we are talking about?

Is 850hpa (for example) always the same height? Or is that dictated by pressure patterns?

Tks in advance

re your last line

no the 850mb just like other heights, 700, 500, 400, 300mb etc is not always the same height. That depends on the pressure at the surface, and to a lesser extent what the actual temperature is. This is how aircraft are able to fly with a constant 1000ft vertical separation between them.

[TEITS]

Been away from the models today so im catching up.. In my eyes an improvement and it does look as though the overall pattern could be shifted slightly further S. The real talking point though is the potential for Scotland especially N Scotland who could potentially see heavy snowfalls and if this pattern of the LP tracking further S continues then Scotland may not even see less cold interludes.

At the moment little for the rest of us to be excited but im focussing more on the output for those in Scotland. I would love to spend the next 7 days in Shetland Isles.

A mean of -8C with some runs dropping to -14C.

http://cdn.nwstatic.co.uk/ensimages/ens.20121221/12/t850Shetland.png

[Jason M]

Ensembles are starting to look more interesting. Quite a few bringing the trough further south and a few channel runners thrown in for good measure. Has the GFS been on the whiskey, or is a pattern change coming?

There is one that shows a 950 mb low roughly over Newcastle, which might be interesting :-)

Jason

[mulzy]

Deep FI on 18z GEFS has a few interesting HLB solutions.

[Zakos]

Yes some very interesting ensembles. All maintain a mobile pattern for the next 144+ hours. No question of that.

However this doesn't neccesarily mean cold shots will be swiftly pushed away.This all depends on the angle/southerly extent of the jet stream, and the path of the lows

perturbation 1 is amazing

followed by this

giving this

An absolute snowfest for some areas.

This is about as good as you can get from cold zonality.

This run is by no means alone, plenty of runs follow this trend of a southerly tracking jet stream. Interesting too see this on the ensembles. As I said the actual outcome will depend largely on the track of the lows, and this will change every run.

After this spell of unsettled weather, hints from the ensembles for more settled and cold conditons