General Model Output Discussion

[snowking]

The ensembles sum up the situation perfectly at the moment.

http://charts.netweather.tv/ensimages/ens.20100109/06/prmslCambridgeshire.png

As you can see high pressure remains close by with the mean at 1020mb.

My view is we're going to remain cold with the flow alternating between SSE/SE/ESE,ly. I can also see a big snow event for Wales/W Midlands/parts of the SW because this is the usual locations that see a stalling front. Beyond next week and at the moment I cannot see any movemenr of our HP to Greenland but instead LP systems continue to track underneath our block keeping much of the UK cold with only the SW possibly turning milder. However with these LP systems tracking underneath the block to the E there is always the chance of retrogression. I just can't see it happening this week.

Whatever happens in future model output will not change the fact that this winter will be remembered for many years. Hard to believe its only the 9th Jan!

I will finally add that the snow event this weekend into monday could be significant. This isn't due to the intensity of the snow but the sheer persistance of it. The heavier snow in the SE will move further N and affect central regions as the flow changes from a ENEly to a E,ly. I feel Monday is going to be an extreme day for much of E Anglia/Midlands/Wales/N England.

I think the other thing is the snow is likely to be really rather dry in nature - add 2-5cms of fresh powdery snow on top of several inches already lying in many areas, along with easterly winds gusting to 30-40mph and you have some serious issues for travel networks

One question RE: the charts paul just posted. Obviously at the moment with the continental feed we are looking at a more and more shallow layer of the troposphere for our weather. Does this mean that even with 850 temps bordering on 0c, with the thicknesses between 850mB and the surface remaining conductive of snowfall, we can to some extent ignore the 850 temps all together or are things not quite that shallow meaning that if the 850 temps get above 0c frozen rain is probably more likely?

SK

[Lakes Tom]

The ensembles sum up the situation perfectly at the moment.

http://charts.netweather.tv/ensimages/ens.20100109/06/prmslCambridgeshire.png

As you can see high pressure remains close by with the mean at 1020mb.

My view is we're going to remain cold with the flow alternating between SSE/SE/ESE,ly. I can also see a big snow event for Wales/W Midlands/parts of the SW because this is the usual locations that see a stalling front. Beyond next week and at the moment I cannot see any movemenr of our HP to Greenland but instead LP systems continue to track underneath our block keeping much of the UK cold with only the SW possibly turning milder. However with these LP systems tracking underneath the block to the E there is always the chance of retrogression. I just can't see it happening this week.

Whatever happens in future model output will not change the fact that this winter will be remembered for many years. Hard to believe its only the 9th Jan!

I will finally add that the snow event this weekend into monday could be significant. This isn't due to the intensity of the snow but the sheer persistance of it. The heavier snow in the SE will move further N and affect central regions as the flow changes from a ENEly to a E,ly. I feel Monday is going to be an extreme day for much of E Anglia/Midlands/Wales/N England.

I agree entirely....I really think the amount of snow to fall from tomorrow afternoon into Monday has been underestimated. The GFS precipitation charts show moderate snow, for upto 24 hours in some parts (Midlands and Northern England look to be the favoured spots). This has been shown on the last few GFS runs....

[Uncle_Barty]

I thought we'd need 1000-850mb thicknesses of around 1290 or less for snow? Above that, it becomes very marginal?

[Nick F]

A look at the fax output currently shows that the old t+96 for 12z Tues has the low further south than the newer t+84 fax for 12z Tuesday, not by much, but perhaps marking a general consensus this morning for milder air to win across the south and southwest. But still some great uncertainty as early as Tuesday from the models with what to do with the lows developing to the SW and how much milder air will infiltrate across England and Wales, of course alot of snow possible preceding any milder air behind fronts getting in.

Have updated my blog for the next few days:

http://forum.netweather.tv/topic/59644-new-year-cold-spell/page__gopid__1727863entry1727863

[benb]

I agree entirely....I really think the amount of snow to fall from tomorrow afternoon into Monday has been underestimated. The GFS precipitation charts show moderate snow, for upto 24 hours in some parts (Midlands and Northern England look to be the favoured spots). This has been shown on the last few GFS runs....

Could well be Lakes Boy,

We're entering a situation the models haven't had to deal with 'live' before. A lot of the data from previous events has been fed in retrospectivley.

It's certainly going to be an interesting progression.

This is why we watch the models.

[J10]

The ensembles sum up the situation perfectly at the moment.

http://charts.netweather.tv/ensimages/ens.20100109/06/prmslCambridgeshire.png

As you can see high pressure remains close by with the mean at 1020mb.

My view is we're going to remain cold with the flow alternating between SSE/SE/ESE,ly. I can also see a big snow event for Wales/W Midlands/parts of the SW because this is the usual locations that see a stalling front. Beyond next week and at the moment I cannot see any movemenr of our HP to Greenland but instead LP systems continue to track underneath our block keeping much of the UK cold with only the SW possibly turning milder. However with these LP systems tracking underneath the block to the E there is always the chance of retrogression. I just can't see it happening this week.

Whatever happens in future model output will not change the fact that this winter will be remembered for many years. Hard to believe its only the 9th Jan!

I will finally add that the snow event this weekend into monday could be significant. This isn't due to the intensity of the snow but the sheer persistance of it. The heavier snow in the SE will move further N and affect central regions as the flow changes from a ENEly to a E,ly. I feel Monday is going to be an extreme day for much of E Anglia/Midlands/Wales/N England.

Slightly off topic but this ties in with the increased Met Office Warnings. http://www.meto.gov.uk/weather/uk/uk_forecast_warnings.html

As for next week I have done a summary in the Welsh thread, about this mornings output.

[Snowyowl9]

Just seen the 6z run and that would be unprecidendent for record snowfall

This chart shows snow all the way until next friday not freezing rain thank goodness.

http://www2.wetter3.de/Animation_06_UTC/144_30.gif

A big blizzard on tuesday with strong/gale force E/SE winds.

Edit:GFS Oz showed light snow even next saturday.

http://www2.wetter3.de/Animation_00_UTC/168_30.gif

Edited January 9, 2010 by Snowyowl9

[Matt12]

I am no weather expert, but it seems to me that the latest GFS ensembles show the cold versus warm battle was never a foregone conclusion. It seems, if anything, that it is trending towards the colder - anyone feel free to correct me if I'm wrong.

[johnholmes]

A look at the fax output currently shows that the old t+96 for 12z Tues has the low further south than the newer t+84 fax for 12z Tuesday, not by much, but perhaps marking a general consensus this morning for milder air to win across the south and southwest. But still some great uncertainty as early as Tuesday from the models with what to do with the lows developing to the SW and how much milder air will infiltrate across England and Wales, of course alot of snow possible preceding any milder air behind fronts getting in.

Have updated my blog for the next few days:

http://forum.netweat...3entry1727863

nice update Nick thanks for that and a very absorbing few days coming up as I suggested a couple of days ago. The developing situation is a classic of winters gone by, and like then, the outcome will not be known until probably 24 hours prior to each attempt of the Atlantic to win out over the cold of the past days, well weeks for some northern and hilly areas further south.

I would not want to have to call the outcome more than 24 hours ahead of each day.

There is no doubt that the intense cold with 850mb temperatures not normally seen for possibly decades over the Uk being almost the 'norm' for the past 3-5 days, will not shift easily. Will it snow or rain, will it be freezing rain, etc are questions that are going to be very hard to answer.

Much of the theory and indeed the empirical rules which have become MOS (Model Output Statistics) fed into the UK Global and Local models is not as robust as it might be in most circumstances.

1000-500mb thickness rules don't work very well

1000-850mb rules ditto

The main reason of course is trying to predict the advection of the milder air. Basic physics shows that cold air is denser and thus warmer air will more readily slide up the cold than bodily shift it. The erosion rate is almost impossible to work out and depends on so many factors. Some like sea temps, proximity to sea, how the local topography reacts to higher temps and dewpoints can be reasonably accurately modelled.

But like I posted several days ago the developing scenario this week is an absolute nightmare for a forecaster. I'd love to be on the wall of the senior man at Exeter but I'm happy not to have to do his job this week or indeed our own man Nick F!

Fascinating it is going to be for sure.

And further ahead-well the fact my lrf is still not out suggests that is very far from clear as well!

Its on its way later today-honest!

Edited January 9, 2010 by johnholmes

[mushymanrob]

I am no weather expert, but it seems to me that the latest GFS ensembles show the cold versus warm battle was never a foregone conclusion. It seems, if anything, that it is trending towards the colder - anyone feel free to correct me if I'm wrong.

is it?...heres derbyshires

http://www.netweather.tv/index.cgi?action=ensviewer;sess=

that shows a real warming up (back to average) over the next 4 days.

[sandstorm2]

is it?...heres derbyshires

http://www.netweather.tv/index.cgi?action=ensviewer;sess=

that shows a real warming up (back to average) over the next 4 days.

The control, mean and operational never get above zero, is that average for your area.

SS2

[Cloud 10]

is it?...heres derbyshires

http://www.netweathe...ensviewer;sess=

that shows a real warming up (back to average) over the next 4 days.

Are you sure?

[Supercell]

is it?...heres derbyshires

http://www.netweathe...ensviewer;sess=

that shows a real warming up (back to average) over the next 4 days.

Potentially moving towards some upper level warmth, but entrenched cold at the surface is hard to shift. Stagnant and dense it undercuts, if it moves at all. I would think that the models would need to trend towards more of an attack / a number of hits from the Atlantic to make a break through. Initial fronts will stall and unload snow / freezing rain, before fizzling out and giving way to cold, dry air once again.

This is something completely different to the typical easy first round knock out of the not-so-sort-after (these days anyway) northerly toppler.

[tinybill]

Latest BBC SE News forecast is for HEAVY SNOW for SE Sat night and Sunday. Up to today prolonged light snow was forecast.

BFTP

all i say last sunday country file was on the money thomas was dead right out side we got a bizzaed blowing and the wind cuting you in half

[sandstorm2]

The control, mean and operational never get above zero, is that average for your area.

SS2

oops looked at the 850's wrong chart.

SS2

[Thundery wintry showers]

is it?...heres derbyshires

http://www.netweather.tv/index.cgi?action=ensviewer;sess=

that shows a real warming up (back to average) over the next 4 days.

It's true that the 850s get pretty close to the long-term average, but you need to bear in mind that 850s with a flow off the continent are going to translate to lower temperatures than 850s with a moist Atlantic flow as part of a generally westerly regime.

Things are really on a knife edge for southern areas at the moment, I'm seeing general agreement that the milder air on Tuesday/Wednesday probably won't get far beyond the south coast, but the GFS also hints at some warmer air coming into East Anglia and the southeast, and possibly as far as the Midlands, for Thursday/Friday, which is also something to watch for.

[Snowly does it]

12z sees the first Atlantic low slide under and the second barrel along through France with no breakdown to mild from either. Uppers will rise briefly above 0 on this run in the West and South before returning to between 0 and -5 throughout in an E to SE flow.

Scandi High more aligned for cold winning and further west on this run.

[Just Below Zero]

Split PV reload complete

Waiting for the next bullet

http://charts.netweather.tv/gfsimages/gfs.20100109/12/135/h850t850eu.png

[KTtom]

http://www.wetterzentrale.de/pics/Rtavn1441.png

Hmmm, this warm up seems to be going the way of the pear Temps still around freezing come Friday.

[bluearmy]

on the 06z run, the upper high was centered over Poland T174. on the 12z, its off the norwegian coast. a good sign with ridging into the north atlantic.

[waynetheweatherman]

Sorry about this as im no specialist on models, however does it look like that for my area (sheffield), look as though its warming up next week and maybe thaw or is it still looking mosly cool?, cheers

[bluearmy]

ukmo 12z run looks pretty good if you want the block to hold on and possibly even win.

[Climate Man]

I know on liners are frowned upon - what about two words.

What breakdown?

[weather eater]

Substantially different 12z run and if this starts showing across the other models then a major climb down will have taken place. An old fashion forecasting nightmare for the next few days.

[johnholmes]

An old fashion forecasting nightmare for the next few days.

very very true as I posted this morning and several days ago(post 110 this morning if you wish to read some comments about it)