Model Output Discussion - 5th December - 11th December

[Catacol]

So far RJS's forecast of strong winds and depressions for the first 2 weeks of Dec is spot on. Models arent yet picking up on the cold arctic air he forecast in the run up to Christmas from the 15th onwards - wonder whether they will start to turn his way...

[Glacier Point]

Hi Chio - I understand the anomaly as compared to average, but when I look at the charts for Jan 2007 they dont seem to fit at all in terms of creating that deviation from average. By Jan 20 there is a deep low off the north of Scotland which would have helped reduce the average pressure, but for the rest of the month it is distinctly ordinary looking, and pressure over Greenland which shows up on the composite as likely to be lots above average looks nothing like.

My point is that GP's chart suggests winds from the NE with pressure deviations encouraging that flow, but if you look at a chart on almost any date in Jan 2007 you dont see a NE wind. The wind was predominantly westerly for most of the month aside from a short easterly flow from around Jan 22 to 25.

So are these composite charts actually not potentially very misleading? I'll say again that I understand they are deviations from average, and not 500Pa charts themselves, but as deviations they imply a particular flow and that flow doesnt match up with the reality of the Jan 2007 charts.

Am I missing something? GP's chart makes me excited for cold; but then a look at Jan 07 makes me wonder why I bothered to think something might happen...

Have a look at the rest of the years there, and also take the hemispheric view. Sure, there will be some variability between years but the general theme across these years (or the common denominators) is depicted there quite nicely. The average Arctic Oscillation for these years in January is -0.568. If the atmosphere is so chaoitic, then anomalies such as these are either due to chance or as a result of one or more drivers exerting a considerable influence on the global weather pattern.

In this instance, the composite analogue (which could be viewed the same way as an ensemble mean, smoothing out the white noise), is suggesting to us that there will be some attempt for the lagged effects of the MJO event in October (or perhaps more so the way the atmosphere is behaving) to raise heights to our north.

Finally, if the composite anomaly is not your cup of tea, or results are pure chance, compare November's mean anomaly for the composite anomaly:

There is not a cigarette paper's difference between these across the hemisphere and that cannot be down to chance alone.

[Liam J]

18z GFS & NAE near identical with the positioning of the storm come Thursday evening, this will be a notable event without a doubt.

[chionomaniac]

Have a look at the rest of the years there, and also take the hemispheric view. Sure, there will be some variability between years but the general theme across these years (or the common denominators) is depicted there quite nicely. The average Arctic Oscillation for these years in January is -0.568. If the atmosphere is so chaoitic, then anomalies such as these are either due to chance or as a result of one or more drivers exerting a considerable influence on the global weather pattern.

In this instance, the composite analogue (which could be viewed the same way as an ensemble mean, smoothing out the white noise), is suggesting to us that there will be some attempt for the lagged effects of the MJO event in October (or perhaps more so the way the atmosphere is behaving) to raise heights to our north.

Finally, if the composite anomaly is not your cup of tea, or results are pure chance, compare November's mean anomaly for the composite anomaly:

There is not a cigarette paper's difference between these across the hemisphere and that cannot be down to chance alone.

Blimey, they are similar!

And if Decembers correlate.....

[on the coast]

Oh dear. Another battering coming in a weeks time or so. No let up with these lows.

[igloo]

yip it looks bad for my neck of the woods i wunder if it will be a repeat of the boxing day 1998 event when we had 110mph winds with chimneys being blown of roofs,and even roofs being blown of houses

Edited December 6, 2011 by igloo

[Frosty.]

The models have changed a lot in the last few days, only a few days ago they were showing high pressure taking control during the coming weekend with a very anticyclonic outlook but that idea has been blown apart and now all we have is a brief flat ridge sandwiched between departing low to the east and advancing atlantic lows. The models today are indicating a strong spell of cold zoneality with wintry ppn for most of the uk although higher snow risk further north, meanwhile, the approaching vigorous depression should melt most of the fresh mountain snow but then it comes back with a vengeance on friday, the arctic air should push snow showers further south than last time and then a frosty night and a chilly weekend, mostly fine on saturday but turning more unsettled from sunday onwards and on the cold side.

[legritter]

JUST WAITING FOR LATEST FAX ,BUT OF COURSE ANY SMALL DETAIL WILL COME LATER . WILL BE ALSO LOOKING OVER NEXT COUPLE OF DAYS FOR HOPEFULLY SOME SORT OF PRESSURE RISE TO OUR FAR N/E VERY FAR ,WE NEED THESE LOWS TRACKING FURTHER SOUTH , BUT I AM CERTAINLY HAPPY WITH THINGS AT THE MOMENT , PLENTY OF ACTION TAKING PLACE TOMORROW DOWN AT EXETER I WOULD IMAGINE , ALREADY READ SOME INTERESTING NEWS SNIPPETS FROM UP NORTH ,BUT MUST BE CAREFULL AS NEWS IS SOMETIMES EXAGGERATED ,AS WE KNOW .BRING ON THE UPGRADES ,CHEERS LEGRITTER .

[johnholmes]

JUST WAITING FOR LATEST FAX ,BUT OF COURSE ANY SMALL DETAIL WILL COME LATER . WILL BE ALSO LOOKING OVER NEXT COUPLE OF DAYS FOR HOPEFULLY SOME SORT OF PRESSURE RISE TO OUR FAR N/E VERY FAR ,WE NEED THESE LOWS TRACKING FURTHER SOUTH , BUT I AM CERTAINLY HAPPY WITH THINGS AT THE MOMENT , PLENTY OF ACTION TAKING PLACE TOMORROW DOWN AT EXETER I WOULD IMAGINE , ALREADY READ SOME INTERESTING NEWS SNIPPETS FROM UP NORTH ,BUT MUST BE CAREFULL AS NEWS IS SOMETIMES EXAGGERATED ,AS WE KNOW .BRING ON THE UPGRADES ,CHEERS LEGRITTER .

does it have to be in capitals?

Still time for the track and depth to change but not only are the Northern isles going to get, even for them, some very high wind values as the winds veer into the NW, I suppose possibly in excess of 90mph but the Forth-Clyde valley? Its very finely balanced as to when the flow goes through the valley and linked into what temperature values are shown in the bottom 2-3000ft but it might be very serious for that area. One I'm sure UK Met are watching closely along with all the already mentioned pssible areas of concern.

Edited December 6, 2011 by johnholmes

[Andy_]

A very weird looking chart from the 18Z GFS, never seen anything quite like that showing up before... It would bring some snow for the west if it verified.

[Fozfoster]

LOL. Does it matter?

does it have to be in capitals?

Still time for the track and depth to change but not only are the Northern isles going to get, even for them, some very high wind values as the winds veer into the NW, I suppose possibly in excess of 90mph but the Forth-Clyde valley?

Its very finely balanced as to when the flow goes through the valley and linked into what temperature values are shown in the bottom 2-3oooft but it might be very serious for that area. One I'm sure UK Met are watching closely.

[stewfox]

does it have to be in capitals?

Only the 'D' ?? ie Does

[feb1991blizzard]

I wish you could bank NWP model runs, GFS 18z is a stonker, that is if you like interesting winter weather.

[k19]

A very weird looking chart from the 18Z GFS, never seen anything quite like that showing up before... It would bring some snow for the west if it verified.

I'm not sure about snow to anything other than high ground... the 850's are too high

[Tim Bland]

Could we see true cold zonality?! With the Jet going south it is possible! Very rare but could give snow to the south!

Edited December 6, 2011 by Tim Bland

[Andy_]

I'm not sure about snow to anything other than high ground... the 850's are too high

-5 850's aren't that high mate, and if you look a couple of frames earlier there were some slightly colder ones across Scotland... I don't think this evolution would happen anyways though it's a bit too disorganised for my liking

[k19]

-5 850's aren't that high mate, and if you look a couple of frames earlier there were some slightly colder ones across Scotland... I don't think this evolution would happen anyways though it's a bit too disorganised for my liking

Apologies it has been a while since I looked at the 850's and the light blue used to indicate -5's and green used be 0's.

[nick sussex]

Could we see true cold zonality?! With the Jet going south it is possible! Very rare but could give snow to the south!

Unfortunately not much chance with that chart, even if the 850's were correct there would be too much modification given the long sea track.

The GFS always overplays the cold in FI, cold zonality generally has lows crossing much further south, often northern areas will remain in the cold, I can't remember the last time I saw true cold zonality.

To be honest our hopes rest with whats been mentioned this evening and some ridging towards Svalbard to force the jet axis nw/se.

[Zakos]

I'm not sure about snow to anything other than high ground... the 850's are too high

Perhaps, but the thickness is very low for a westerly - http://hw.nwstatic.co.uk/gfsimages/gfs.20111206/18/189/hgt500-1000.png

A few small upgrades could see this become a snowfest.

[Andy_]

Apologies it has been a while since I looked at the 850's and the light blue used to indicate -5's and green used be 0's.

No bother! I get a bit confused when switching between Wetterzentrale's charts and Netweather's too like... I prefer the latter though!

[Kentish Kiwi]

As I've stated before, it might not look exactly like this due to La Nina, but could there be very tentative signs of the tropospheric polar vortex at least becoming stretched into an odd shape, which might open the door for wave breaking into the stratospheric vortex at the end of the month ?

By this do you at all mean you expect there to be a more NE/Eerly component to the wind direction, with stronger blocking over Scandinavia, rather than the general northerly that seems to be illustrated GP?

That particular composite for January looks rather similar to the kind of set-up experienced midway through December 2010 to my decidedly amateur eye...

[BLAST FROM THE PAST]

So far RJS's forecast of strong winds and depressions for the first 2 weeks of Dec is spot on. Models arent yet picking up on the cold arctic air he forecast in the run up to Christmas from the 15th onwards - wonder whether they will start to turn his way...

Indeed and the signs are beginning to show.

BFTP

[Cloud 10]

Interesting looking at the current state of the AO and the NAO which are both positive,the AO notably so.

Certainly doesn't look conducive to the sort of weather i've experienced over the last few days with max temps of 2c

[Zakos]

GFS 18Z, yet another run dominated by polar maritime air. Most of UK under sub 528dam air for majority of run, with a few mild blips. Occasional cold enough to produce low level snow from the midlands northwards

If this were to verify, would each polar maritime shot be more and more likely to produce snow as each shot would slightly cool the SST'S?

[EastLothianSnow]

does it have to be in capitals?

Still time for the track and depth to change but not only are the Northern isles going to get, even for them, some very high wind values as the winds veer into the NW, I suppose possibly in excess of 90mph but the Forth-Clyde valley? Its very finely balanced as to when the flow goes through the valley and linked into what temperature values are shown in the bottom 2-3000ft but it might be very serious for that area. One I'm sure UK Met are watching closely along with all the already mentioned pssible areas of concern.

Hi John,

Although i don't post very often i do read the forum on a daily basis and enjoy reading your posts, very informative. Being on the coast in East Lothian we are used to getting some high winds, the worst i can remember being in December 1998 when they peaked at over 100mph and ripped some structures down and tore roofs of buildings. Could we be looking at similar strengths in my neck of the woods on Thursday evening/night into Friday? Could you explain what you meant with your reference to the temperature values that are shown in the bottom 2-3000ft?

Thanks

Edited December 6, 2011 by SuperRangers