Model Output Discussion - 5th December - 11th December

[Frosty.]

The stormy spell for late thursday and friday looks every bit as severe as the storm we had on thursday, this one actually looks worse if that is even possible considering there were gusts well in excess of 100 mph and 165 mph over the summits of the cairngorms and mean wind speeds of over 60 mph but the storm later in the week looks ultra destructive and will affect the whole of the uk although the core of the most severe winds is still to be determined. It also looks very wet at times with heavy rain associated with very active fronts but since they will be fast moving, the intense rain won't last long in any location. There is likely to be a sting in the tail as the storm system pushes into the low countries next weekend with the floodgates opening to an arctic airmass for a few days with a risk of snow and ice and widespread frosts but then there are continued signs of high pressure becoming centred to the southwest of the uk in the immediate run up to christmas with milder sw'ly winds swamping the north and west of the uk but perhaps colder and brighter in the southeast with fog and frost for a time, it then looks like the colder zonal pattern will eventually blast the benign pattern away southeast as the gfs 06z suggests and there is a chance of snow on christmas day if the cold zonal weather has displaced the higher pressure by then.

Edited December 11, 2011 by Polar_ Low

[Michael Winston]

The beebs forecast for the week ahead by Peter Gibbs pushes the worst of Fridays LP system to the North of the UK if this keeps going the way it is nothing then we should be able to breathe a huge sigh of relief.

Hi Gavin.

True, but he did say that the uncertainty at this range is great. Like yourself though I hope he's right.

Kind regards,

Mike.

[Great Plum]

For those worried about Christmas, the 06z op was a mild outlier at the end... See:

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

[Frosty.]

The beebs forecast for the week ahead by Peter Gibbs pushes the worst of Fridays LP system to the North of the UK if this keeps going the way it is nothing then we should be able to breathe a huge sigh of relief.

and that is gospel is it?

[Thundery wintry showers]

I don't agree with Gavin D, because the northern extent of these lows is often correlated with the severity. If the low tracks further north, it might result in ordinary rather than severe gales for England and Wales but it could increase the chances of Scotland and northern England getting hurricane force winds. Moderate structural damage over a large area would be less problematic than demolition over a small area. Many recent runs have highlighted this with the runs that take the low further north giving a deeper low.

The UKMO version would be a severe gale for most parts of the UK but nothing exceptionally dangerous, while the ECMWF operational goes for something more serious especially for Ireland.

The longer-term outlook still has a ridge of high pressure coming across the south following the northerly, but again the odds are roughly 50-50 IMHO on a mild last third of December vs. a brief milder interlude and then more stormy weather with average temperatures.

[lorenzo]

This animation tracks the peak gusts. It is clear there is still a sever impact unless tracks change.

[rich1]

For those worried about Christmas, the 06z op was a mild outlier at the end... See:

http://www.netweathe...;type=ens;sess=

Did follow the 00z in being the main run to go for a mild snap around the big day period for more than about 36-48 hours, one idea hopefully they will drop, as they did at one time for the Euro high to dominate December [which it hasnt]

not ideal but have to see what we can get in a week or so when we may get a clearer idea. Wouldnt be against a UK high with frost and fog but looks like cool-coldish zonal from the ensemble output versus the euro-bartlett op GFS runs against some possible weakish scandinavian-blocking on ECM

I hope something more interesting emerges before too long if I am honest. I will be going to the tropics [where I am semi-permanently based] from the second week of January, would be a bit of a dead loss this winter for me if nothing appears before then

[DaBrigg]

Even the ECM is on board with some sort of extreme event.just look at the isobars!

Maybe this storm needs its own thread?

Yesterday morning's ECM also had a very compact storm, with extreme winds over a smaller area, taking a similar similar track across the northern fringes of Ireland and into Central Scotland.

Long time model watchers like myself are used to seeing the GFS occasionally overdoing storms at his timeframe, only to tone them down a little closer to the event, but this consistency from the ECM, along with reasonable agreement from the UKMet, is worrying. (or promising, depending on your viewpoint).

Incidentally, Ive only just noticed those weatheronline charts apparently don't show pressures lower than 950hpa, perhaps I'm a little slow.

[A Winter's Tale]

Another update from Simon

[damianslaw]

It will be Wednesday at the earliest before we have a good idea of Fridays projected storm path - it is a very worrying feature it has to be said and quite rightly is the main topic of discussion at the moment.

It could take a very similiar path to last Thursdays storm in which case southern highlands/central belt would be worse hit. It could take a more southerly path meaning southern scotland and n england would be worse hit..

Its a difficult call at this stage, but people should be prepared for the worse. I am travelling over to Newcastle on thursday eve was toying with the idea of leaving it until Friday but not now!

In the short term - more of the same, generally chilly wet and windy. tuesday will be a very windy day for many with gales and more wintry showers in the north.

Longer term - next weekend looks like being cold with northerly winds so chance of wintry showers for many more so northern parts - could be a good dusting in places by end of the weekend which will deliver a festive feel. The period 18-21 Dec in recent years has often delivered a cold picture - and in very zonal decembers as well think dec 99.

I'm not speculating on the run up to christmas just yet, the projected storm next friday will have a major impact on conditions thereafter in determining where height rises may build.

[TonyH]

Guide to the weeks weather Monday December 12th to Sunday December 18th (west Wales and central Midlands specific)

Very windy, with damaging gales possible Tuesday, and again late Thursday to Friday. Rain or showers, hill snow, average to rather cold temps

Winds should drop off enough tonight for a slight frost for most.

Dry and bright to start Monday but cloud, wind, and then rain into west Wales though the afternoon, leading to a wet evening here, and then rainy for the Midlands overnight.

A very deep low close to Scotland on Tuesday so a very windy day with gales, and potentially severe gales causing damage during Tuesday for west Wales. Blustery showers and quite a cold day. Rather cold and windy on Wednesday with more showers, these heavy with hail, especially over west Wales, and where hill snow is possible, also perhaps with a longer spell of rain.

A brief ridge of higher pressure permits lighter winds and clearer skies Wednesday night with a slight frost. A frosty start Thursday, but the next storm system is approaching. This one is an explosively deepening low as it rapidly crosses the Atlantic, deepening from 990mbar Wednesday evening to perhaps as low as 930mbar during Thursday night, when it will be somewhere over the UK, and could be our deepest and most severe storms for a few years! It depends on the exact track as its still 4 days off, but should the centre pass through northern England, then Wales and the Midlands would see severe, destructive gales on Thursday night into Friday morning. However, should the low track further north, we would be spared the worst, but still gales for all of us. Areas worst affected will be seeing winds over 100mph, and with a more southerly track even the Midland would get 80mph gusts, so plenty of damage and danger is possible. Needless to say heavy rain for all, along with the gales, this turning to wintry showers on Friday and into the weekend, although any snow should be restricted to the high ground of Wales.

At this stage next Sunday hints at calmer, drier, conditions but frosty.

For supportive model charts see here:

http://forum.netweather.tv/topic/69041-wales-regional-weather-discussion/page__st__400__gopid__2180467#entry2180467

[jonnybradley]

Thanks Winters tale, very interesting update from Simon again.

Noob warning!! Again guys please correct if I am barking up the wrong tree here. *

Think I posted a couple of days ago that it is hard to see past Fridays storm (would this be where FI is at the mo?). I agree with Simon that the models are having a bit of a time sort out the period after Fri. As damianslaw points out, will be hard to pin the placement of Fri low till Tue has blown trough and Fridays is a bit closer to our shores.

I think it will be interesting to see how these lows interact with the high in the Atlantic and I assume this will effect the pattern of things to come. *

Very interesting times, certainly a lot more going on than when I started watching here back in mid Nov!

Thanks All, keep up the good discussions.

Jon

Edited December 11, 2011 by jonnybradley

[OldMetMan]

I'm in general agreement with you, OMM, but with one qualifying point. The core of the jet is forecast to be coming from an almost due westerly point across the Midlands on Thursday/ Friday rather than its usual steering trajectory from SW to NE.

The low approaching for Tuesday has been shifted gradually north/ north west on the models and the jet is firmly recurving northwestward close to north west Scotland.

If the fearsome looking jet core on Thursday/Friday maintains its current track would not the tendency be for the centre of the low to be steered on a more due westerly course, rather than the more usual north westerly?

Hi Terminal Moraine, thanks.

You could well be right, I am basing what I say on what Ihave seen happen in the past. Lows of such intensity as forecast distort the upper flow considerably, and it is a well known phenomenon that rapidly deepening lows always turn to the left as they deepen.

What is clearly critical to the storm's path is exactly when and where the rapid deepening occurs. If that happens well before the storm approaches our shores, then it may well turn NW and perhaps only the N and W of the country will be worst affected (looking at the newly issued Met O warnings, this seems to be their thinking at the moment).

On the other hand, if the main deepening happens later, as the storm is coming into Ireland say, then yes, a more westerly track is entirely possible. This is more or less what happened on Thursday last, the track of the low being to the N of Scotland with the isobars squeezed along its southern flank.

In my experience, there are 2 main types of situations where a core of extreme winds can form around a low; one in a warm sector where the pressure gradient is squeezed ahead of the associated cold front (as happened in October 2000 for example) the other as happened on Thursday with the main action happening after the frontal zone has passed through. (the Burns Day storm I mentioned is also a good example). Such extreme gradients tend to be on the southern (SW or SE) flank of a low.

As far as the models go in handling this storm, there has been a remarkable similarity between individual runs of each model, plus a consistency between the different models themselves. Personally, in this situation, I would be more inclined to trust the UKMetO output which during today and tomorrow will begin to show what the GFS/ECM are now showing.

In any event, I would suggest that from about Tuesday/Wednesday onward, all the models should have a pretty good handle on the ultimate track and intensity of this storm. Until then, an awful lot could change.

[ukpaul]

Met Office maps appear to have the strongest winds in places like Sussex and Kent for both of the coming storms - Mon/Tue and late Thurs (Friday isn't up yet).

Is there any reason for that, I would have thought places like Fort William would be much higher if the track of the LP was as is being suggested? Is it because of the winds, on the track that is being suggested, whipping their way unimpeded up the channel?

[Nick L]

Met Office maps appear to have the strongest winds in places like Sussex and Kent for both of the coming storms - Mon/Tue and late Thurs (Friday isn't up yet).

Is there any reason for that, I would have thought places like Fort William would be much higher if the track of the LP was as is being suggested? Is it because of the winds, on the track that is being suggested, whipping their way unimpeded up the channel?

Probably to do with the fact that the strongest winds of a low pressure system are typically on the southern side of the centre.

[TonyH]

The beebs forecast for the week ahead by Peter Gibbs pushes the worst of Fridays LP system to the North of the UK if this keeps going the way it is nothing then we should be able to breathe a huge sigh of relief.

However he did stress that the shown chart was likely to be different come the time due to track uncertainty this far out, implying the system may well be further south as much as further north,

[Nick F]

Met Office maps appear to have the strongest winds in places like Sussex and Kent for both of the coming storms - Mon/Tue and late Thurs (Friday isn't up yet).

Is there any reason for that, I would have thought places like Fort William would be much higher if the track of the LP was as is being suggested? Is it because of the winds, on the track that is being suggested, whipping their way unimpeded up the channel?

I think it's more to do with where the pressure gradient will be steepest when the fronts move through late Mon into Tues from the west - i.e. southern England/Channel. Also there is a strong low-level jet across southern England late Monday/early Tuesday.

It gets very windy in the north and northwest later on Tuesday though, as a deep low arrives close to the NW.

[Cloud 10]

A couple of charts from the 06z gfs at +78 showing the sharp temperature gradient associated with the low as it develops,and also the strength of the jetstream

Looks like more model watching coming up.

[A Winter's Tale]

Looks like more model watching coming up.

I think you'll need to be hinding behind the couch sometime next week. Really, the current charts are quite terrifying.

[Frosty.]

The latest 6-15 day meto update again has a wintry flavour for next weekend with wintry showers likely in most of the uk but with the main snow threat for northern britain and with widespread frosts, most interesting is the further outlook which suggests a toning down of any settled weather with the very unsettled and windy pattern with heavy rain at times tending to have more dominance but with shortlived calmer interludes with frosts which IMO implies brief ridging between depressions, still no sign of anything majorly wintry from the models but no sign of anything particularly mild either, any mild spells look brief but it's really the strong winds which will grab all the headlines again with a fairly average windy spell early in the week followed by the monster storm later in the week but tomorrow looks like the most pleasant day of the week and wednesday should also be ok.

[nick sussex]

The latest 6-15 day meto update again has a wintry flavour for next weekend with wintry showers likely in most of the uk but with the main snow threat for northern britain and with widespread frosts, most interesting is the further outlook which suggests a toning down of any settled weather with the very unsettled and windy pattern with heavy rain at times tending to have more dominance but with shortlived calmer interludes with frosts which IMO implies brief ridging between depressions, still no sign of anything majorly wintry from the models but no sign of anything particularly mild either, any mild spells look brief but it's really the strong winds which will grab all the headlines again with a fairly average windy spell early in the week followed by the monster storm later in the week but tomorrow looks like the most pleasant day of the week and wednesday should also be ok.

I know everyones rightly more interested in these storms given how much impact they could have but longer term I think the uncertainty is beginning to grow in terms of the prospects for Xmas and into the New Year.

You could make a case for several scenarios, trough locked in over Europe and Azores high kept further west, or a Euro high with a milder flow especially for northern areas, a Euro high with surface cold or an easterly.

Edited December 11, 2011 by nick sussex

[bluearmy]

the ecm ens for london now have the xmas period showing. the mean seems fairly average amongst a wide spread

http://www.weathercast.co.uk/services/ensemble-forecast.html

at this time, it would seem very unlikely (as expected) that the southern half of the uk will see any festive weather come the big day. however, it also doesnt seem likely that we will be looking at the mild conditions shown on some of the recent gfs op runs. i noticed NAEFS 00z had dropped the mean uppers back to zero over the whole country, right through the next fortnight (transient warm sectors apart).

[saintssupporter]

http://www.youtube.com/watch?v=3jEKgrE5Mzc&feature=g-u james corden update

[saintssupporter]

james corden update

http://www.youtube.com/watch?v=3jEKgrE5Mzc&feature=g-u

[Summer Sun]

Latest track for the storm on Friday

http://www.wetterzentrale.de/pics/Rtavn961.png

http://www.wetterzentrale.de/pics/Rtavn1021.png

http://www.wetterzentrale.de/pics/Rtavn1081.png

Hard to tell what the center pressure is but it will be low.