Model Output Discussion - 19th - 25th December

[snowlover2009]

Obviously with the odds of a SSW taking place, thank God and I know it does not guarantee cold. But I guess the models will adjust and take ionto account the SSW when they pick it up, therefore can we expect colder runs showing there hand and more blocked scenarios in FI?

I always thought like many others the second half of winter will be the coldest and I think by around new Year time, this place is going to be a very exciting place to be. I expect the models to start giving us some tasty runs and about time too. One only needs to take a look at the cfs run from this morning and know what I mean. The reason I think the models will have more interest around new year time is because I expect the key time for a dramatic pattern change to occur around the second week. Just think if this pattern change comes off and we are to get height rises, which I think is quite likely looking at GPs composites and the February one is brilliant, we will be far away from the horrid autumn pattern we had to endure. December has not been to bad though.

Edited December 22, 2011 by snowlover2009

[Thundery wintry showers]

Christmas Day's weather looks like having a NW-SE split. Danm from London mentions a preference for dry and sunny over wet and windy, and "dry and sunny" might prove to be an accurate description of Christmas Day's weather in London, as well as many other parts of central, eastern and southern England. Northern and western Scotland and NW England and north Wales, however, will probably end up dull with some rain or drizzle. Intervening areas are likely to end up dry and cloudy.

[sandstorm2]

Now I know it is the CFS charts and can't really be trusted, but just take a look at the frigid air moving into GB from the continent. Unfotrunately it is a chart for the begnning of FEB but maybe, just maybe GP is going to hit the bullseye with his winter forecast.

Don't know how to post the charts.

SS2

[chionomaniac]

Just a reminder - NO SSW is forecast to occur presently.

Edited December 22, 2011 by chionomaniac

[shedhead]

The models are making more of the high pressure to the SE during the period 22nd-27th December, suggesting that it won't be a mild grey drizzly scenario everywhere. Many parts of eastern England are seeing some sunny intervals today, and after the polar maritime incursion on the 23rd/24th December, high pressure looks set to continue ridging into the SE on the 25th-27th. Thus, the 25th-27th will probably be dry with broken cloud and sunny intervals across much of central, southern and eastern England, and in any sunshine it will feel notably warm out of the wind. Other regions, though, probably will end up grey and drizzly.

The low pressure for the 28th/29th is prone to considerable uncertainty, and I won't be surprised if it largely disappears on future runs. There is, though, a consistent signal for a colder anticyclonic end to the month with brighter weather extending further north and west.

Disagree with this. Whilst the latest output suggests it won't be grey and drizzly everywhere, temperaturewise the period from now until the 27th will be mild overall, perhaps locally very mild. I do agree tho that given any sunshine, particularly in the lee of high ground and out of the breeze, the words 'notably warm' probably do not represent an over exaggeration.

[Thundery wintry showers]

I think you've read things into my post that aren't there, as the rest of the post refers clearly to sunshine amounts and not lack of mild temperatures- in fact I mentioned that in any sunshine "it will feel notably warm out of the wind".

[Frosty.]

I beg to differ Karl, FI is definitely looking like a change in New year is possible. 06Z has come up with interesting LP/Feature on 27th [can't post links]. Interesting because I felt that around Boxing Day we could see some gales with LP hitting us. Models had this showing last week in FI but generally ditched the idea with just a very breezy SW'ly set up. Is it something to watch? Some Colder air digging in behind it up north/Scotland. BFTP

I'm not too convinced about that LP feature you mentioned fred, the 6z does show a risk of snow in scotland around the middle of next week with a N'ly blast skimming eastern britain but I don't think it had any other support. I think the north of the uk will have a mild, wet and windy weekend, especially mild on xmas day, drier further south but mostly cloudy, very mild and breezy, then we may catch a break in the bad weather early next week with high pressure and some slight frost risk and then a mix of mild and cool zonal towards new year and into 2012 with a flat jet, low pressure to the north, high pressure to the south..it all has a familiar ring to it.

[Tim Bland]

Glad to see GFS 06z OP was a mild outlier in FI ESP for the south

[Methuselah]

Just looked at the GFS. And, apart from one or two temporary incursions of PM, I can't discern any major pattern-change. That said, as British weather is characterised by pattern-changes; eventually, a pattern-change is inevitable, IMO.

[chionomaniac]

With the only teleconnective change a decrease in the overall westerlies, I don't think that we will see any major changes in the GFS output just yet.

I think we could possibly see changes in the ECM output a little sooner as forecast changes aloft are more pronounced on the ECM.

I will be interested on the ECM 32 dayer tomorrow. I wonder will anything be picked up with those ensembles.That could depend on whether the tropsopspheric ECM output is determined by actual or predicted changes in the stratosphere.

[Iceberg]

Chino,

There might be some signs I think if you have a look at the GFS 06Z and the period from T300 onwards on a N.Hemi view you see the model take a massive pressure build with a strong cross polar flow dragging the really frigid air straight down the middle of the states due to the rex block.

The huge block 1050mb seems to me to be forced out of the warming that is occuring at the 10hpa layer.

First time I've seen a true cross polar flow this winter caused by such blocking and I can't believe it's total coincidence.

It ties in well with the PV moving eastwards with less strength and then a re-organisation of the HP cells as we move further in Jan.

Cheers

[chionomaniac]

Chino,

There might be some signs I think if you have a look at the GFS 06Z and the period from T300 onwards on a N.Hemi view you see the model take a massive pressure build with a strong cross polar flow dragging the really frigid air straight down the middle of the states due to the rex block.

The huge block 1050mb seems to me to be forced out of the warming that is occuring at the 10hpa layer.

First time I've seen a true cross polar flow this winter caused by such blocking and I can't believe it's total coincidence.

It ties in well with the PV moving eastwards with less strength and then a re-organisation of the HP cells as we move further in Jan.

Cheers

Well spotted, I hadn't looked that far out on the NH view.

[phil nw.]

Well spotted, I hadn't looked that far out on the NH view.

This is it for anyone interested

http://www.meteociel...&mode=0&carte=1

It`s posted to show upper heights modelled around the area where the strato.warming is forecasted to raise hts--not to be taken as gospel.Like Iceberg has suggested that this may be the first signs that the 500hPa pattern is responding.

Edited December 22, 2011 by phil n.warks.

[dragan]

Lots talking about strat warming today. Am i to be right saying, tomorrow Met O 16-30 day forecast should be reflect this??????? They usually get things right.

[Isolated Frost]

The european upper-temps as of 3pm GMT... white colours indicate the 850's at 0c, and every time the colour changes, there is a loss (if it turns more blue) of 2c in upper temps, and there is a rise (if it turns more orange) of 2c in upper temps. The darker the colour, the further away from 0c uppers it is, but of course it's easy to work that out yourself.

A good tool when tracking airmass changes or for a quick view. You can see the most deep cold in E Europe/Russia, which substantially milder air in the west and south.

Here is britain at 6am tomorrow, you can see the clearly defined cold front there, should be fairly potent not due to the fact there is cold air behind it (only -4c/-5c 850's for most so nothing noticeable), but because of the evidently very mild airmass it will be replacing.

[bluearmy]

i think the latter stages of the gfs suite will struggle to give an accurate indication just yet. yesterday we had what looked like a dsplacement of the p/v to siberia at the end of the 00z run. today we see signs of it splitting at the end of the 06z run. this may well be a response to the pressure being put on the p/v by the warming at the top levels of the strat. however, we need to see some consistency in response from the outer reaches of the model before we get a handle on what current and forecast events in the strat will have on the patterns in the trop.

[geoffw]

which is more reliable - the ECM or the GFS stratospheric forecast?

[BLAST FROM THE PAST]

I'm not too convinced about that LP feature you mentioned fred,

Tell you what, look at the 12z ukmo 120-144, BOM has it too. I think its back on the table. Further edit 12z GFS has it too

BFTP

Edited December 22, 2011 by BLAST FROM THE PAST

[Grimsby Snow Lover]

Something new on the FI charts I feel. Could someone explain whether the 1016 high in the top centre is the first signs of the warming stratosphere? The reason I ask is because for the past 6 weeks or so the colours up there have been either blue or purple reflecting the strength of the PV. Thanks

http://hw.nwstatic.c...276/h500slp.png

It is also good to see lower hight over southern Europe and a diving southerly tracking jet. Hopefully a new trend as this will keep us in the colder more seasonal side

Edited December 22, 2011 by Grimsby Snow Lover

[Zakos]

Something new on the FI charts I feel. Could someone explain whether the 1016 high in the top centre is the first signs of a blocking high pressure? The reason I ask is because for the past 6 weeks or so the colours up there have been either blue or purple reflecting the strength of the PV. Thanks

http://hw.nwstatic.c...276/h500slp.png

PV forecast to split?

[mountain shadow]

Something new on the FI charts I feel. Could someone explain whether the 1016 high in the top centre is the first signs of the warming stratosphere? The reason I ask is because for the past 6 weeks or so the colours up there have been either blue or purple reflecting the strength of the PV. Thanks

http://hw.nwstatic.c...276/h500slp.png

Something strange going on anyway. Normally we see heights building into the north from the mid latitudes, that High over Svalbard just seems to build in situ.

[Climate Man]

Certainly the models look as though they are trying to pick up something. Early signs of a pattern change and indeed heights are trying to build in some interesting areas. Next couple of days may well be interesting.

[Grimsby Snow Lover]

Something strange going on anyway. Normally we see heights building into the north from the mid latitudes, that High over Svalbard just seems to build in situ.

Thanks! All relative I suppose as by the end of the run its pretty much as you were.

[chionomaniac]

Something strange going on anyway. Normally we see heights building into the north from the mid latitudes, that High over Svalbard just seems to build in situ.

The 100 hPa charts have suggested a 'light' split of the vortex ie not penentrating up into the strat - we now can see quite clearly on the NH the effects from above.

[Climate Man]

Thanks! All relative I suppose as by the end of the run its pretty much as you were.

It is not quite as you were with the Jet much further South and not as flat. The interesting part is the "wobble" mid run and not the end output.