Winter Model Discussion - The Hunt For Cold -12z 14/12/12

[Whether Idle]

I don't think they are Dave, we know we will be seeing pressure rise over Iberia and we know we have the High to the NE. The only doubt is how far East into Europe the jet gets. Weak HP around Greenland is academic, because the upper Atlantic Low is in place and can go nowhere. We are going to be stuck in this rut until something changes upstream.

Im sure the strat. warming will propagate down in time to save us before winter's end. Did the job last year for many!

Edited December 16, 2012 by Whether Idle

[chris55]

The big three models now showing an undercut of some kind at 120, this looks to be an evolving pattern towards a colder outlook rather than the usual warm up as we get nearer. Nothing certain, but the trends are heading the right way. Yesterday GFS had the Atlantic just storming through, we still need some changes to get a sustained colder outlook for a larger portion of the UK, but with the evolving pattern anything is possible.

Although the Azores high is still in the mix, but recent runs have diluted it's influence a little.

Also note the Barents sea Low on all three runs, this, IMO, is what we need to see cutting (in some fashion) through the Russian high.

Edited December 16, 2012 by chris55

[Frosty.]

.

You are sick and need help. No I *Personally* do not want a record breaking sunshine filled Christmas day and *you* should wash your mouth out or rinse your keyboard for saying such things, Yuck!!!!!!!

We should be happy with whatever comes our way, we are weather fanatics and should embrace all types of weather and I am not going to let the models drag me down if they flatter to decieve in FI like they did this morning with the freeze shown on the gfs and ecm 00z, there is way too many mood swings on here when the models don't give us what we want in our own back yards. Records are there to be broken so just enjoy what comes our way, mild or cold.

Edited December 16, 2012 by Frosty039

[Ian Brown]

Im sure the strat. warming will propagate down in time to save us before winter's end. Did the job last year for many!

By a literal skin of it's teeth for Eastern Britain.

Lets see if christmas day can be as warm as last year, we had 15c on the big day last year so that would be quite amazing if that record is broken, statistically we are more likely to get snow at easter than xmas anyway. The models are trying to give us another bbq christmas heatwave. if we can't have a nice freeze, lets break another kind of record.

Yes, could be interesting and of course not unlike many of the late 80s and 90s Xmas days.

[LomondSnowstorm]

If I recall correctly we had cross model support for a Christmas northerly just this morning and have the UKMO 12Z showing an easterly into eastern Scotland by D5, so we can't exactly pretend that there's much confidence in the details past day 4 and certainly not in terms of even the broader pattern past day 7. The undercut is the first detail to be sorted out but after that a lot depends on upstream signals and the willingness of the heights to the east and south to stick around.

[Weather-history]

Yes, could be interesting and of course not unlike many of the late 80s and 90s Xmas days.

I think you mean like most of the 1970s and 1980s Christmas days? Winning a bet on white Christmases since 1990 increased, 1993, 1995, 1996, 1999 you would have won a bet.

[chionomaniac]

A number of off topic posts have been removed.

Please keep on topic and relevent, thanks.

[nick sussex]

I think we're now facing a race against time to save Christmas! cue Hollywood music!

Close but no cigar doesn't cut it and the output just seems intent on keeping the cold air tantalisingly close to the east.

We just can't seem to get a clean ejection of shortwave energy and this really is what its coming down to.We need a good correction south and west in the outputs and the shortwave needs to separate from the main troughing with no residual energy left behind.

The battle of the Azores high being pushed ne in response to that upstream amplification and the block to the east still has room for some manoeuvre, however we don't have much time to play with, Santas on life support and I fear the machine maybe switched off tomorrow unless we see some overnight changes!

I should add once the opportunity passes for that ne/e flow then you want rid of the Russian high as then it just acts as a block to cold if the upstream pattern stays amplified.

Edited December 16, 2012 by nick sussex

[russell k]

If I recall correctly we had cross model support for a Christmas northerly just this morning and have the UKMO 12Z showing an easterly into eastern Scotland by D5, so we can't exactly pretend that there's much confidence in the details past day 4 and certainly not in terms of even the broader pattern past day 7. The undercut is the first detail to be sorted out but after that a lot depends on upstream signals and the willingness of the heights to the east and south to stick around.

Totally agree "Lomond" Just look at the spread on the (midlands) ens, nothing past D5/6 is anywhere near cast in stone...cold or mild await ecm ens with int.

[Gibby]

Good evening. Here's my report on the 12zs from GFS, UKMO and ECM for today Sunday December 16th 2013.

All models show a basic pattern over the coming week though the details in any one place may easily change. The current showery Westerly flow in association with the Low pressure moving into the UK currently weakens on Tuesday as a weak ridge of High pressure crosses gently East over the UK. In the Atlantic a large and deep depression will be taking shape with associated troughs approaching the SW with rain spreading slowly North and East over the UK midweek. With the cold high pressure block out to the East the rain may well stall later in the week with further Low pressure running into the UK by the weekend maintaining a risk of high rainfall totals in places in temperatures near normal or maybe somewhat below in the North.

The GFS operational goes on to show deep low pressure forming close to the UK drifting out into the North Sea in the run up to Christmas with yet more heavy rain followed by colder and showery weather in strong North or Northwest winds with wintry showers in most places. Over the Christmas period this run shows winds backing towards the West with any chances of a real white Christmas restricted to the higher Northern hills with rain showers elsewhere in brisk winds. In the period after Christmas the weather turns decidedly milder with moist SW winds and a lot of dry weather in the South with high pressure not far away over France, while the North remains more unsettled with some rain while New Years Day shows less mild and dry conditions with overnight frost and fog possible.

The GFS Ensembles show a massive spread on range of upper temperatures from next weekend with all sorts of options on the table for Christmas and beyond. On balance though I would say that the milder options still hold sway with plenty of precipitaion on offer for all areas through the run.

The Jet Stream shows the flow blowing strongly from West to East just to the South of the UK where it is progged to stay through the next 7-10 days though with some undulation North then South at times.

UKMO for midday on Saturday shows Low pressure in mid Atlantic and East over the Baltic with High pressure over Northern Russia. The UK lies in the path of a trough lying close to Southern Britain with rain here while the North sees weak influence from a ridge extending down from the NE drawing colder air in from the East.

ECM shows slack Low pressure over the UK at the weekend with cooling air in slack winds making for an enhanced risk of frost and fog to form widely with some rain or showers in places too. The Low pulling the trough into the SW over the weekend wins the battle on this run with a wet and windy Christmas on the cards as Low pressure becomes influential to the North of the UK with near to average temperatures at the surface.

In Summary there is a standoff later this week between the cold blocking High to the East of the UK and Atlantic depressions wanting to move across the UK and on into Europe. The net result is a UK battleground where low pressure actively moves into the UK then disrupts, with a lot of the energy weakening in situ over the UK in preparedness for the next Atlantic attack. This duly arrives in time for Christmas making the emphasis to a green rather than white Christmas being the most likely outcome. Nevertheless, with such wide spread between the Ensemble members there is a chance of changes as we move through this week if the block decides to be more resilient than currently shown. The one common denominator between all models is that there is likely to be plenty of rainfall over the duration of the output run with only limited chance of frost, ice and snow for Northern hills on current showing.

[Frosty.]

Countryfile forecast looked vague at the end of the week, very much like the models today, some showing undercut and others not, as for FI, it does look very mild at times but since the models still haven't nailed the pattern after midweek, a record warm or record cold christmas is still possible, but more likely something fairly average.

[Matty M]

ECM EPS............................Not good i think the bulk of the UK can write off the easterly incursion. Scotland, particularly northeast Scotland still at risk.

Perhaps we now move to the potential for the northerly incursion towards Christmas Day/ St Stephens Day

[nick sussex]

ECM EPS............................Not good i think the bulk of the UK can write off the easterly incursion. Scotland, particularly northeast Scotland still at risk.

Perhaps we now move to the potential for the northerly incursion towards Christmas Day/ St Stephens Day

Yes they look very solid on the low pressure getting just too far north and east and theres little spread on the ensembles for the Azores high ridging ne.

I'd agree re Scotland and perhaps ne England having a chance of something a bit more wintry, thereafter we really need to look to the nw for salvation.

I'd give it one more run but unless theres some changes there then I think its time to concentrate on hoping the upstream pattern can deliver a north/ nw .

[The Eagle]

12z GEM @ 120hrs FWIW

[damianslaw]

The models continue to chop and change in the medium outlook, GFS and ECM earlier were suggesting the azores high exerting influence by the middle of the week with mild southerly/southwesterly airflow, now they are showing the russian high exerting a block on the low pressure system forcing it on a direct southerly course for the country with the trough forced to split and send a shortwave undercut of sorts preventing the azores high from exerting any influence - temps for most average, and in the north a little below average. Such an evolution could easily results in height rises to just to the NE of us before christmas..

With this kind of chopping and changing within the 72-96 hr timeframe, its best to expect further changes in future runs, as it suggests the models are struggling with the strength of the russian high.

There are many options on the table as we head into the christmas period. If the russian high maintains its position and strength then we will be left either with the trough languishing over the country with lots of rain and average temps, slightly below in the north, or stronger heights just to our NE and a more settled cold picture. If the russian heights begin to loose intensity then there will be much less forcing on the atlantic trough and we could then either see a deep low moving into scandi and northerlies following as was shown in the GFS and ECM output as we head to christmas day, or the azores high exerting greater influence pulling in a mild southwesterly flow as being toyed with by GFS this evening.

Its a real head scratch at the moment... best advice might be just to take each day as it comes and expect the 'unexpected' and you won't be dissapointed. I said in a previous post, the christmas period is notorious for being a very difficult time of year to predict weatherwise, when major sudden changes often do occur within very short timescales catching all forecasters out. This year looks no different.

[bluearmy]

Uncertainty re how the atlantic comes through and how long it takes but the ecm ens seem pretty sure that by day 7 it will be to our east. The spread on xmas day is very low, showing a strong depression around n britain. It would seem this mornings ecm run is more reliable than this evenings op with a ridge to our west at the end of the run although it may be transient but tough to tell where that surge of very low heights is headed as they march sw out of the polar field to our north.

[Frosty.]

Countryfile showed a bit of wintry ppn for the northern tip of scotland on friday, not sure if that is being conservative but anyway, midweek is the major wet and windy period and still a chance of some undercutting for the far north and north east but the midweek low seems to just raise the temps further south and west after the rain has moved through. I have seen some complex charts in my time but these take some beating with the level of uncertainty at such a short range, any radical changes in the week ahead will have a major ripple effect on the further outlook to chrisrmas and new year, I still have hopes of a potent Northerly between xmas and early next year but whatever will be will be.

[nick sussex]

Countryfile showed a bit of wintry ppn for the northern tip of scotland on friday, not sure if that is being conservative but anyway, midweek is the major wet and windy period and still a chance of some undercutting for the far north and north east but the midweek low seems to just raise the temps further south and west after the rain has moved through. I have seen some complex charts in my time but these take some beating with the level of uncertainty at such a short range, any radical changes in the week ahead will have a major ripple effect on the further outlook to chrisrmas and new year, I still have hopes of a potent Northerly between xmas and early next year but whatever will be will be.

I saw that forecast and DB seemed to be using the 00hrs output, unless they modified the 12hrs then that forecast was recorded much earlier.

The Friday forecast could look rather silly if their 12hrs output verifies.

Showing a bit of sleet in the Highlands doesn't correlate with this output, maybe its got no ensemble support or maybe the forecast is recorded before they have looked at the latest output but DB had better hope that UKMO 120hrs doesn't verify!

Edited December 16, 2012 by nick sussex

[Frosty.]

I saw that forecast and DB seemed to be using the 00hrs output, unless they modified the 12hrs then that forecast was recorded much earlier.

The Friday forecast could look rather silly if their 12hrs output verifies.

Yes that's what I thought, it looked a bit vague after midweek, it seems that confidence in the forecast drops rapidly after wednesday, probably be resolved by tomorrow though surely. Fax charts are eagerly awaited tonight.

[nick sussex]

Yes that's what I thought, it looked a bit vague after midweek, it seems that confidence in the forecast drops rapidly after wednesday, probably be resolved by tomorrow though surely. Fax charts are eagerly awaited tonight.

Unfortunately Frosty those fax charts given the current set up will probably change again tomorrow, at least for northern areas things are less clear cut.

If the fax charts follow the UKMO raw output then expect the BBC to highlight a bit more uncertainty in later forecasts.

[mountain shadow]

Its time we wish the block to head east to allow pressure to fall over Scandinavia and increase the northerly potential.

Maybe the pub run will give a bit of Christmas cheer.

[I remember Atlantic 252]

Its time we wish the block to head east to allow pressure to fall over Scandinavia and increase the northerly potential.

Maybe the pub run will give a bit of Christmas cheer.

Agree with that, fed up of this russian high, get it out the way, bring in northerlies for Xmas, not being stuck in no mans land,

[NL]

Well the latest NOAA CPC 8-14 day 500Mb chart is showing high pressure to the NE of the US and LP over BI dragging down a possible northerly/nor'easterly.

[OldMetMan]

As i see it, the models are struggling a bit at the moment. It is interesting to note that from what appeared to be a fairly straightforward case of the Atlantic systems seeing off any possibility of a cold air incursion, what is apparent now is that it may not be the case.

Yesterday, I noticed one of the GEM runs had frontal activity stalling and a new HP building the E. Today, I saw the 00Z GFS bringing us some bizarre cold conditions and the UKMet seems also to be backing off somewhat with a more slow-moving frontal approach.

I have also noticed a couple of things that are bugging me and which appear to have some bearing on whether the cold air will - eventually - make it.

1. There is still cold air advection heading W across Europe, courtesy of the large Russian HP.

2. Although it is not very strong, there still exists a 500mb high over Greenland.

Now I know for a few days the GFS in particular has been amplifying the upper flow pushing some very mild air up over us ahead of deepening Atlantic systems but the runs are changing in a subtle way, with more trough disruption happening along each frontal boundary that crosses the UK. This has also been the case with some of the other models.

I have been describing a number of scenarios whereby we could get a return to cold conditions, mostly because I have witnessed the kind of synoptic configuration we have now a number of times before and, although the battle between mild and cold had been quite prolonged at times, in nearly every case, the cold air has won out.

Here's the 500mb chart for today:

Apart from the Greenland high, the Russian upper high is still there and the jet is still low-latitude. With Atlantic systems predicted to turn NE pushing warm air ahead of them, this will, I think, help to maintain the Greenland high, plus it will also keep a meridional flow in place over much of the Atlantic and W Europe. In other words, it does not look the kind of arrangement which would allow a full scale over-run by the Atlantic.

What I suggest is happening basically is that this warm/cold struggle will continue for a while yet. High pressure will be maintained over Greenland and over much of W Europe and eventually, either from the N or NE, a significant incursion of cold air will happen. I base this to a large degree on what I have seen happen historically.

In particular, we need to keep an eye out for cold air starting to head S to the N of Scandinavia, such as suggested by the end of the last GFS run.

All this could take a while as I said, but it will be fascinating to see how the models will handle it.

[legritter]

Certainly looking very interesting after tuesday ,potential flooding issues for many ,fronts could slow down giving high rainfall totals .but beyond friday i would not like to forecast with a couple of options possible up to christmas and just after . if only we could get pressure to fall further south and a bit of greeny height rises it could all so change ,anyhow GFS now churning out its predictions ,will we see a mega run ,then all taken away whilst we sleep .catch up tomorrow after ECM .