Model Output Discussion - 12th December Onward

[Great Plum]

A lot of talk about a mild Christmas but look at the 06z ensembles for London:

http://www.netweather.tv/index.cgi?action=charts;type=ens;sess=

An outlier in FI... Some interesting options in some of the ensembles for cold and the mean is trending around average...

[rug]

Very interesting ensembles , seem to be continuing the below average theme.

[Chris Jennings]

where i live in norfolk have had any decent snow for many a years in fact we are heading for a drought, but with nao going negative maybe harsh winters ahead :smilz38:

[Frosty.]

so the mild SW winds get going at +204 on 6z. Nailed.

As BFTP has said, we are heading towards a new pattern and unfortunately, in the transitional phase it looks like a milder spell is unavoidable for most of next week but at least the cold snap at the end of this week has more bite than the last one and the milder weather will hopefully get shunted away during the christmas period, it's still unclear how much influence the high to the south/southwest will have, if it's being modelled too far north, there is a chance of cold zonal returning around xmas eve/day/boxing day. As for the new year, i'm really excited about the potential for a big freeze developing in january.

[Cecil Hogmanay Melchett]

where i live in norfolk have had any decent snow for many a years in fact we are heading for a drought, but with nao going negative maybe harsh winters ahead :smilz38:

nao looks to be positive .

[Glacier Point]

Taking the ECM day 6-10 ensemble mean as guidance, programs up to around 21st December.

http://raleighwx.ame...htAnomalyNH.gif

The main features worth considering are the trough projected into Europe and development of the ridge in the Atlantic, which is assumed by some here to become a Euro ridge.

In so far as the trough is concerned, the key question will be just how much energy is deflected south-east into the Asian Jet, which in turn will have an influence on the Russian High ? As we are talking developments getting close to January, there is some question mark as to how quickly and how much energy lifts out poleward given the Winter Forecast suggests lowering of pressure over Europe in January.

The ridge development to our west looks OK, but just how far east will it get and will it stay there ? With a strongly posiitve AO, there would be some teleconnective support for a Euro ridge getting close to January. However, still minded by a general trend from the composite analogues (including those MJO ones) for a tropospheric change into January ahead of the stratospheric one so the potential here for that ridge to our west to wobble around and back west and northwards sliding energy across the UK into mainland Europe -wouldn't be suprised to see the core of the high parked just to our west for lead up to Christmas week.

Edited December 12, 2011 by Glacier Point

[Cecil Hogmanay Melchett]

quite a wintry update from the metoffice not going with gfs 06z one iota.

[WhiteFox]

so the mild SW winds get going at +204 on 6z. Nailed.

Nailed to what? The form horse?

Anyway, taking a look at the H500 charts, the change starts to occur this weekend even as the toppler is upon us:

We're still just about in the trough, but the ridge to the west is pushing through which will ultimately cause the mid-Atlantic ridge to topple and deliver the milder air from the West. 36 hours later, and the influence of the uper ridge is being fully felt:

The mid-Atlantic ridge starts to fold allowing the milder SW airstream to flow over the top of the high pressure. Of course, H500 charts can be wrong, but they rely less on the minor adjustments to systems that we see on SLP charts and give an indication of trends in the weather. In the 6z GFS we are left in the influence of a strong ridge which remains more or less in situ; occasionally flattening to allow Westerly airflow, but generally mild to very mild. It can be wrong, and will be wrong on the details past a certain time of course, but the trend on the H500 charts is for a ridge to setup close to the UK which will deliver High pressure to the south, both at the surface and at higher levels (unlike the oh so transient Greenland highs we've seen unfortunately).

The trend is there; in order to see this change, we'd need to see changes upstream, which at the moment don't appear to be in the forecasts. The US is also looking zonal from after the weekend as the powerful jetstream in the Pacific crosses unabated into the West Coast, preventing any real amplification from delivering colder air further south.

That's my non-expert take on it all anyway...

[shedhead]

Taking the ECM day 6-10 ensemble mean as guidance, programs up to around 21st December.

http://raleighwx.ame...htAnomalyNH.gif

The main features worth considering are the trough projected into Europe and development of the ridge in the Atlantic, which is assumed by some here to become a Euro ridge.

In so far as the trough is concerned, the key question will be just how much energy is deflected south-east into the Asian Jet, which in turn will have an influence on the Russian High ? As we are talking developments getting close to January, there is some question mark as to how quickly and how much energy lifts out poleward given the Winter Forecast suggests lowering of pressure over Europe in January.

The ridge development to our west looks OK, but just how far east will it get and will it stay there ? With a strongly posiitve AO, there would be some teleconnective support for a Euro ridge getting close to January. However, still minded by a general trend from the composite analogues (including those MJO ones) for a tropospheric change into January ahead of the stratospheric one so the potential here for that ridge to our west to wobble around and back west and northwards sliding energy across the UK into mainland Europe -wouldn't be suprised to see the core of the high parked just to our west for lead up to Christmas week.

Cheers for the update GP, I'd settle for that rather than the hairdryer, perhaps the hope of something a bit more seasonal for extreme eastern areas of the country at least?

Edited December 12, 2011 by shedhead

[phil nw.]

06z Gfs op was a massive mild outlier! Lots of options on the table still! I expect a rolercoaster on here as some cold scenarios pop up over the coming runs!

Yes whilst the approach of the Azores high after the weekend appears the likely scenario the GEFS show the mean 850`s running below 0c and the Op run very much the milder option in the lower resolution period.

http://hw.nwstatic.co.uk/ensimages/ens.20111212/06/t850Warwickshire.png

That still indicates uncertainty on where any High situates,it could be a High building further north or pushed back south quickly from another burst of North Westerly`s. .

A look at the postage stamps are interesting

http://www.wetterzen...nspanel2401.gif

some colder runs in there.

Edited December 12, 2011 by phil n.warks.

[WhiteFox]

Yes whilst the approach of the Azores high after the weekend appears the likely scenario the GEFS show the mean 850`s running below 0c and the Op run very much the milder option in the lower resolution period.

http://hw.nwstatic.c...arwickshire.png

That still indicates uncertainty on where any High situates,it could be a High building further north or pushed back south quickly from another burst of North Westerly`s. .

A look at the postage stamps are interesting

http://www.wetterzen...nspanel2401.gif

some colder runs in there.

Indeed, it's all about the positioning. There's even the requisite Easterly on there... Anyway, most seem agreed on High pressure to the south, the question is over the exact positioning. Slightly further west and south, and we get NW airflow instead of SW. Exact details to be confirmed, but the high certainly looks likely.

[Frosty.]

it's still unclear how much influence the high to the south/southwest will have, if it's being modelled too far north, there is a chance of cold zonal returning around xmas eve/day/boxing day.

I agree haha

Edited December 12, 2011 by Polar_ Low

[johnholmes]

Taking the ECM day 6-10 ensemble mean as guidance, programs up to around 21st December.

http://raleighwx.ame...htAnomalyNH.gif

The main features worth considering are the trough projected into Europe and development of the ridge in the Atlantic, which is assumed by some here to become a Euro ridge.

In so far as the trough is concerned, the key question will be just how much energy is deflected south-east into the Asian Jet, which in turn will have an influence on the Russian High ? As we are talking developments getting close to January, there is some question mark as to how quickly and how much energy lifts out poleward given the Winter Forecast suggests lowering of pressure over Europe in January.

The ridge development to our west looks OK, but just how far east will it get and will it stay there ? With a strongly posiitve AO, there would be some teleconnective support for a Euro ridge getting close to January. However, still minded by a general trend from the composite analogues (including those MJO ones) for a tropospheric change into January ahead of the stratospheric one so the potential here for that ridge to our west to wobble around and back west and northwards sliding energy across the UK into mainland Europe -wouldn't be suprised to see the core of the high parked just to our west for lead up to Christmas week.

I would agree with your views as shown above Stewart. Just taking the 10-15 day period and the 500mb anomaly charts and not attempting to take it beyond the end of December. To me there seems little to suggest very mild over the Christmas period and the tilting of the flow you refer to seems about 60% prob at the moment. 20% for the flow to stay much as it is and another 20% for it to turn SW and bring the much milder air north.

Another 2-3 days, both to clarify the complex development of the low for Thur-Fri and how the anomaly charts continue over the next 2-3 days should make it a lot clearer for the Christmas week.

[Zakos]

Indeed, interesting ensembles. A couple go for -10 t850's in the south. Clear outliers. However,the. GFS operational is also a clear mild outlier, with little support in FI. A noteworthy number of ensembles go below -5 in the south, some significantly so around Xmas. Interesting.

[bluearmy]

the ecm ens mean for london is the coolest yet this season in fi. the gefs 06z pb's throws up more interesting runs for cold than any run i've seen so far this month. the meto updates today lessen the leaning to mild in the 30 dayer, despite there being no updated ecm 32 day run due till this evening. infact the 15 dayer for the north of the uk is quite seasonal and points to 'fun in the snow' over xmas for those able to get into the hils midlands northwards. all in all, and finally - the main reason for optimism for coldies is ian's persistant call for the 'hairdryer' over xmas !!

[Paul_1978]

It might be FI Paul, but when was the last time we saw GFS produce a different evolution from T+180hrs? At least this time last week they were toying with greater amplification and some

cold shots in the pre Xmas week, but across the last 20 or so runs they have been very consistent and as I said previously, if they had been modelling bitter cold for Xmas in the same way

this forum would be in overdrive.

(I was just correcting Tinybill's constant use of the term F1 instead of FI). ;-)

[Gavin Hannah]

I've seen quite a few models over the last week try to reintroduce the high from the south for the last week or so now. I don't believe we will see this high returning unless it's in the 2-3 day time frame.

For me, it's zonality all the way to Xmas, trending cooler in the south with heavier and heavier snow falls in the north on the backsides of systems passing over us.

[BLAST FROM THE PAST]

As BFTP has said, we are heading towards a new pattern and unfortunately, in the transitional phase it looks like a milder spell is unavoidable for most of next week but at least the cold snap at the end of this week has more bite than the last one and the milder weather will hopefully get shunted away during the christmas period, it's still unclear how much influence the high to the south/southwest will have, if it's being modelled too far north, there is a chance of cold zonal returning around xmas eve/day/boxing day. As for the new year, i'm really excited about the potential for a big freeze developing in january.

Hi Karl

to clarify, next week isn't looking mild IMO, its likely to be coldest week of Dec [3rd week of Dec 15-22]. I also say the ridge will be more robust IMO and not collapsed after 12-24hrs.

BFTP

Edited December 12, 2011 by BLAST FROM THE PAST

[Spurry]

Not a regular poster on this thread , due to lack of knowledge , however i have to comment on what appears to be the uncertainty of the models in the short term,particularly the GFS, this time yesterday we were expecting a battering on thurs/fri with horrendous winds ,it now appears that the low is gonna be tracking further south over France, which will transfer the winds to France,things will probably change again by Thursday , but i suppose overall it means that FI is probably about 2-3 days at the moment(has it ever been so near? )

Edited December 12, 2011 by Spurry

[Glacier Point]

the ecm ens mean for london is the coolest yet this season in fi. the gefs 06z pb's throws up more interesting runs for cold than any run i've seen so far this month. the meto updates today lessen the leaning to mild in the 30 dayer, despite there being no updated ecm 32 day run due till this evening. infact the 15 dayer for the north of the uk is quite seasonal and points to 'fun in the snow' over xmas for those able to get into the hils midlands northwards. all in all, and finally - the main reason for optimism for coldies is ian's persistant call for the 'hairdryer' over xmas !!

Indeed Nick, the ECM 00z and 06z GFS spreads are 'interesting' towards Iceland and Scandinavia at around day 8 so a slight peturbation towards decreased westerly flow has an option to extend the mean ridge further north and waft more cold air back westwards over Europe. Probably too much energy over the top at this stage for this to be a serious player but underlines the complexity beneath the veneer of current model output as we enter a potentially very tricky period (last week or so of the month)for the models.

[casparjack]

Maybe I missed it amongst all the bickering, but I haven't seen any reference to the FAX chart for 0600 tomorrow; it shows the 'middle' low at 943mbs, this still has the potential to be very notable...

Edited December 12, 2011 by casparjack

[Methuselah]

I would agree with your views as shown above Stewart. Just taking the 10-15 day period and the 500mb anomaly charts and not attempting to take it beyond the end of December. To me there seems little to suggest very mild over the Christmas period and the tilting of the flow you refer to seems about 60% prob at the moment. 20% for the flow to stay much as it is and another 20% for it to turn SW and bring the much milder air north.

Another 2-3 days, both to clarify the complex development of the low for Thur-Fri and how the anomaly charts continue over the next 2-3 days should make it a lot clearer for the Christmas week.

Does that mean that Piers might have got it wrong - again?

[Weather Wonder]

Not a regular poster on this thread , due to lack of knowledge , however i have to comment on what appears to be the uncertainty of the models in the short term,particularly the GFS, this time yesterday we were expecting a battering on thurs/fri with horrendous winds ,it now appears that the low is gonna be tracking further south over France, which will transfer the winds to France,things will probably change again by Thursday , but i suppose overall it means that FI is probably about 2-3 days at the moment(has it ever been so near? )

I have seen FI within the 2-3 day range before, last december being a recent example of FI being so close.

With the currently predicted track of the storm over france i think something we need to keep an eye on is the posibility that this storm could stregnthen and track futher north bringing strong winds over southern counties.

Edited December 12, 2011 by Weather Wonder

[ukpaul]

I was just checking this morning's runs and saw below average temperatures for London throughout the ensemble runs and that the Friday low had, on various models, moved further south and become potentially more of a problem for many of us down here.

Then I read here that we are on for a mild (and in an occasional case very mild) run up to Christmas and beyond and that Friday's' storm was significantly downgraded!

If I'm being charitable this looks look a severe case of collective IMBY!

I have seen FI within the 2-3 day range before, last december being a recent example of FI being so close.

With the currently predicted track of the storm over france i think something we need to keep an eye on is the posibility that this storm could stregnthen and track futher north bringing strong winds over southern counties.

This is my major concern, that the storm track now being more southerly would mean that any increase in intensity on that track would push the resulting more intense low up over Southern England. Hopefully that won't happen but it is something to be careful about. Still, there's little agreement as to exact track yet so we can only imagine the many possibilities.

[Iceberg]

This time I'll stick to something a bit more certain, Rainfall in the next 24 hrs looks to be very very high in the Central southern areas, with 50-60mm over the next 24 hrs according to NAE.

considering that Rivers are running quite high atm and that we have plenty more rain to look forward to this week, we could be looking at some quite severe flooding in a few areas.

Particularly if the LP takes the more southerly route later in the week.