General Model Output Discussion

[LomondSnowstorm]

GFS very exiting for next Thursday night/Friday morning in the South

Not too shabby in northeast England and Eastern Scotland either! The 18Z is an upgrade in the eyes of most people I suspect, with those of us in Scotland and northeast England having less chance of convective showers of rain/sleet on Wednesday while southern areas have more of a shot of getting snow instead of rain. Perhaps for northwestern England and northern Ireland this is a bit of a downgrade but to be honest the situation there was always pretty unlikely to develop into a major snow event.

[❄️❄️❄️❄️❄️❄️❄️❄️❄️]

A Mean of sub -8C covering most of the country at 144

[NorthantsSnow]

LOL @ the GFS' not so subtle backtrack since last night. Compare the two charts below for 6am Wednesday:

GFS 18z Mon http://cds030.lo1.hwcdn.net/c9s4a5k3/cds/gfsimages/gfs.20091227/18/60/h850t850eu.png (T60)

GFS 18z Tue http://209.197.11.75/c9s4a5k3/cds/gfsimages/gfs.20091228/18/36/h850t850eu.png (T36)

[yamkin]

We will see, obviously this is a dig at me. Normally people would be posting the GFS PPN charts to illustrate tomorrow, obviously the model has backtracked from its aggressive Northward forcing of the Low.

GFS 18Z looks much better tonight, so here are some charts:

[TEITS]

I have to smile at that ensemble mean, how many times have you posted something like that as one of the ensemble members at something like T216 over the years ? Now its T72 and actually going to happen !

Far too many times mate.

Whats especially exciting with the model output is the potential for this to be prolonged. I noticed GP posted the 8-14 day outlook and the general trend of a block to our NW continues. What also fasinates me with this cold spell is with all the cold temps, lying snow across the continent what on earth would happen if a bitter E,ly arrives later on in the winter. This would be especially raw compared to recent years.

Back to tomorrow and to be honest im actually getting annoyed with the uncertainity. I don't know why but I have this sneaky feeling the precip will not be as far N as the models suggest and would put the N limit around Lincs. I also believe that come tomorrow evening/night the BBC forecasts will have alot more white blobs than they currently have!

[BLAST FROM THE PAST]

I would agree with Joe B/BFTP in respect that much of Jan will be cold. However I don't agree that it will be severe blizzards every day. This would be very unusual and apart from 1947 no other cold spell has ever delivered this. What you have to remember is even the cold winters of 1963 has spells of dry, very cold weather.

Just for the record I did not say or expect every day. 3 possibly 4 bouts of heavy snow, locally blizzard conditions and bitter cold and severe windchill but 3 weeks of very cold to severe cold weather. Agree there will be 'less' cold periods but this stint will hold its own against the big boys. First local blizzards knocking on the door and bitter winchill knocking on the door.

BFTP

[Paul]

Back to tomorrow and to be honest im actually getting annoyed with the uncertainity. I don't know why but I have this sneaky feeling the precip will not be as far N as the models suggest and would put the N limit around Lincs. I also believe that come tomorrow evening/night the BBC forecasts will have alot more white blobs than they currently have!

NMM hi-res model doesn't take the main band as far north as the GFS that's for sure:

850-1000 thicknesses interesting too (blues = a risk of snow, with the deeper blues indicating the higher risk for those who aren't used to these charts)

[Frosty.]

Stunning 18z, the gfs suddenly appears popular again after all the mud that was thrown at it during the last 2 days, funny how it coincides with upgrades for the southeast . Anyway, the second phase of wintry weather is now evolving rapidly and should continue into next week but lots of action before then either in the form of coastal snow showers blown in on a fresh to strong NE'ly wind or the more persistent concoction of rain/sleet and wet snow further south.

[TEITS]

NMM hi-res model doesn't take the main band as far north as the GFS that's for sure:

850-1000 thicknesses interesting too (blues = a risk of snow, with the deeper blues indicating the higher risk for those who aren't used to these charts)

Cheers for posting that Paul.

By the way I shall be sending you a PM tomorrow morning as I want to sort out NW extra. Im confused what to do as i've forgotton my previous login details.

Back to the models and the Cambs ensembles have to be the biggest backtrack I have ever known since following the models.

http://charts.netweather.tv/ensimages/ens.20091228/18/t850Cambridgeshire.png

P.S if anyone is concerned about the rise, don't be as this is often the case.

[MKN]

NMM hi-res model doesn't take the main band as far north as the GFS that's for sure:

850-1000 thicknesses interesting too (blues = a risk of snow, with the deeper blues indicating the higher risk for those who aren't used to these charts)

your precip chart just so happens to be 1 where the precip band is already on its way back, so to suggest it isnt as far north isnt really quite accurate, as its similar to the last nmm output.

[kold weather]

Stunning 18z, the gfs suddenly appears popular again after all the mud that was thrown at it during the last 2 days, funny how it coincides with upgrades for the southeast . Anyway, the second phase of wintry weather is now evolving rapidly and should continue into next week but lots of action before then either in the form of coastal snow showers blown in on a fresh to strong NE'ly wind or the more persistent concoction of rain/sleet and wet snow further south.

I think its also something to do with the fact the 18z is a million times better with regards to the synoptics as well!

Anyway some better agreement finally on a cold ENE/NE airflow developing. Some uncertainties however with regards to if any shortwave cuts off the easterly flow, its possible if the LP to our SE remians strong enough to throw out a secondary depression but even that could quite easily evolve into a snowy set-up.

At the moment at the very very very least we are looking at a 5 day cold spell once the low clears out of the way, but possibly very much longer as well.

[SnowBallz]

What I don't get is this... we've all seen how the GFS model has 'backtracked' quite a lot in terms of the progression of this LP to our SW, and it was the only one which was sticking it waaay more North than the others. Agree right? Well, doesn't that say that there's something wrong with that modelling system then? Does it not also suggest then that, until it's proved itself again, then ALL of its outputs should be the one given less attention? Seems a bit odd that the GFS can be proven to be way off course, yet people still get excited about the very next model it chucks out? What's to say that that model run isn't going to be miles off as well?

Personally I think I'm learning that GFS is a bit of a mickey mouse model - dreamers paradise but shouldn't really be taken seriously. ECM seems to be more of a solid looking thing, and UKMET is the business. Never bother thinking of the weather beyond 5 days because you might aswell just roll a dice (which is what the GFS models seem to do at that sorta range)

just my tuppence anyway.

[Paul]

your precip chart just so happens to be 1 where the precip band is already on its way back, so to suggest it isnt as far north isnt really quite accurate, as its similar to the last nmm output.

Not sure about that - the chart you've posted from 18z is actually showing the precip further south than the 21z chart I posted - run the animation on there and you'll see the northward movement continues up to the 21z chart and then it starts to fade back from the north.

It's also quite different to the 12z run:

12z:

18z

[Rob Deacon]

http://www.null/two/ensembles/

The ens look alot better for cold for london than they did 12 hours ago, not much in the way on ppn though

[john w]

Well...00:27 N24 BBC forecast are relatively confident about the snowline it would seem.

A very long rain event for the SE and Southern areas though....

Takes a while for the severe cold to penetrate south though but by the weekend looks pretty raw for most of UK. Agree with TEITS on the above. Wet day tomorrow for anyone really, some will be white, some will be blue...some a mixture. If the M4 is the dividing line then where I live will be seeing rain :S

[WhiteFox]

Well...00:27 N24 BBC forecast are relatively confident about the snowline it would seem.

A very long rain event for the SE and Southern areas though....

Takes a while for the severe cold to penetrate south though but by the weekend looks pretty raw for most of UK. Agree with TEITS on the above. Wet day tomorrow for anyone really, some will be white, some will be blue...some a mixture. If the M4 is the dividing line then where I live will be seeing rain :S

If only it was a solid line where we saw snow to the north and rain to the south. Would be an interesting drive anyway!

I think by dividing line we are looking at rain to the north of the M4 with some bursts of snow mixed with rain. Any actual settling snow further to the North, with the Chilterns probably being favourites (the M40 between Wycombe and Stokenchurch will probably be testing driving!). Further north, more snow to lower levels, but even at this range it's tight to call. Upper temps look to be fairly high for much of the early event; currently the -2 isotherm runs pretty much along the M4! Far too high for snow wirh air temps between 0 and 2oC... The GFS doesn't seem to dig the colder air down before Thursday; the FAX charts look to have fairly high thickness until Thursday, so any acccumulating snow looks like waiting. I'm with John Holmes in that I think the most accurate charts up to t48 - t72 are the FAX charts...

[kold weather]

http://www.jp2webdes.../two/ensembles/

The ens look alot better for cold for london than they did 12 hours ago, not much in the way on ppn though

Yep decent agreement on a cold set-up till at least the 9th, after that some of the milder runs aren't actually all that mild at all at the surface as they raise uppers as a upper high forms over the UK. Some runs once again very progressive as well.

Also worth noting that the ECM op run was on the milder side of its ensembles suggesting it too was somewhat quicker then the mean of the ensembles would be expecting.

Remember with the models, just because they are wrong/right sometimes doesn't mean next time they won't pick up the right/wrong solution.

[Eugene]

Stonking runs again this morning i really do like GME i must say

http://www.wetterzentrale.de/pics/Rgme1321.gif

Some strange people on TWO looking ahead to after T+300 hrs, everything upto T+168 hrs to me points towards a very long cold spell which even with a worse case scenario euro high will stay cold for ages.

ps GFS 00Z early next week isnt a snow to rain event at all, we stay on cold side.

[If Wishes made Weather]

Interesting 00z from the GFS which now suggests that the low stays in the western approaches and does not make it as far as the channel. All going very ECM.

Met office remain candid and are uncertain about northern extent of the PPN and where/if it will be snow.

It would seem appropriate to watch the continental models (ECM and German DWD model) since that appears to be where the weather will be coming from for the next couple of weeks.

[xerxes]

Stonking runs again this morning i really do like GME i must say

http://www.wetterzentrale.de/pics/Rgme1321.gif

Some strange people on TWO looking ahead to after T+300 hrs, everything upto T+168 hrs to me points towards a very long cold spell which even with a worse case scenario euro high will stay cold for ages.

ps GFS 00Z early next week isnt a snow to rain event at all, we stay on cold side.

LOL - Looking into the distant parts of any output is fairly irrelevent at the best of times IMO but currently all we can say is that the trend is cold, if not very cold once the front retreats away to the SE. 2010 looks to have a bitter start to say the least, and with general model agreement

[HotCuppa]

amazing how it goes from -5.6C at 2.15am to 1.2C at 645am and the dew point already past marginal 0.3C.

Quite interesting this system because so far all we have seen in the nw is the increase in temps.

From this system very cold very dry weather..maybe a few snow showers after the new year if we are lucky in the nw.

would love to see real 'bitter temps' you know -30 -40C quite an experience I can tell you, and thats with out windchill too.

Edited December 29, 2009 by HotCuppa

[Iceberg]

Looking at the global patterns and still no sign on the ECM of moving out of the cycles of the last few weeks. The Omega block is in place towards the end of the run and the upstream pattern is good for yet another reload.

GFS is still a bit scatty, but the trends are there.

So basically an easterly, a northerly (by an upper LP moving directly south), encroaching SW lows, GH then build again, turn the temp dial down a bit and repeat.

[karyo]

Looking at the global patterns and still no sign on the ECM of moving out of the cycles of the last few weeks. The Omega block is in place towards the end of the run and the upstream pattern is good for yet another reload.

GFS is still a bit scatty, but the trends are there.

So basically an easterly, a northerly (by an upper LP moving directly south), encroaching SW lows, GH then build again, turn the temp dial down a bit and repeat.

From what I can see, the 0z ECM brings something less cold from 144 hours as the approaching low get's too far west and cuts off the cold flow. This was also shown on the 12z but to a lesser extend.

Karyo

[Iceberg]

Looking at the thicknesses they seem to be colder than the pre chirstmas LP that came from the north, even at 240 the whole country (except Kent is under 528 or lower.

The ECM site charts(geopotential 500) shows the cold pool moving due south.

Still along way off though, but it's not something I would like to bet against.

[Frosty.]

Stunning 00z output, GEM is a classic run with a bitter NE'ly becoming a sustained N'ly next week with plenty of snow showers for northern & eastern areas. The ecm is also a very cold run, especially for the north with a N'ly also developing next week with a low pushing south, it would bring heavy snow to scotland. The ukmo run is also very wintry and the general idea of the models is to turn the flow N'ly as high pressure to the north begins to pull west and allow an arctic low to slip south...all good news for extending the cold spell well into next week with no real end in sight yet. Today though it looks like the snow will be piling up in upland wales and west midlands with 4-6 inches likely but south of the M4 it will probably be a rain or sleet mix with 4c in london but still mild in plymouth at 10c, the cold air will win out everywhere during the next few days though.