General Model Output Discussion

[Barb]

Nice channel low on Wednesday night/Thursday morning.

[Methuselah]

Maybe slightly OT?? But (if I remember correctly?) the White Xmas of 1968 was 'marginal' meteorologically...I recall heavy rain turn through sleet into a right dumping over a period of several hours...I think that the precip started at about 4C or so?? It can happen!

[johnholmes]

latest 09z chart showing, rather shakily, where the front is and the larger pressure falls, bitter over the N Isles now.

09z on left with, for comparison the 06z chart on the right

[kold weather]

06z GFS still brings the LP northwards across the UK for xmas eve/day, mild in the SE but the cold air remains in the north on this run...

Thats nt before yet another big snow event for the Se section of the country, the far SE becomes too marginal but from London Northwards it'd be a big snow event, a proper cutter so to speak...

[Tom D]

Even out at +165, this 06z run is very similar to the 00z. Two runs in a row showing a deep low tracking over France and somewhat stalling over the UK, before a beast of a low in the Atlantic rears its ugly head for the last week of the decade.

[johnholmes]

Its interesting to see, courtesy of Wx Online how cold last night was after the discussions about GFS showing values too low.

Topcliffe (28 m)-13° Dishforth (33 m)-10° Birmingham (99 m)-9° Benson (57 m)-9° Cottesmore (142 m)-9° Tees-Side (37 m)-9° Sennybridge (307 m)-9° Shap (249 m)-9° Linton-On-Ouse (14 m)-9°

so two places already had -10C or below.

I'll wager there will be more over the next 2-3 nights?

[Nick L]

Its interesting to see, courtesy of Wx Online how cold last night was after the discussions about GFS showing values too low.

Topcliffe (28 m)-13° Dishforth (33 m)-10° Birmingham (99 m)-9° Benson (57 m)-9° Cottesmore (142 m)-9° Tees-Side (37 m)-9° Sennybridge (307 m)-9° Shap (249 m)-9° Linton-On-Ouse (14 m)-9°

so two places already had -10C or below.

I'll wager there will be more over the next 2-3 nights?

I was just thinking this myself John. The GFS was predicting maximums of -2 or -1c across large swathes of central England earlier in the week, here it is still -4c, so there is more proof that the GFS doesn't always go insane with the minimums. The Met Office are going with -8c and -9c on Tuesday and Wednesday nights, so those who repeatedly slate the GFS for going mad with minimums should do a bit more research!

Edited December 19, 2009 by nick2702

[Barb]

Agreed about the minimums, BBC Wales forecast me -3c last night when it got down to -7. Other places in Wales had similar or lower figures too.

[Tom D]

Agreed about the minimums, BBC Wales forecast me -3c last night when it got down to -7. Other places in Wales had similar or lower figures too.

That's why I don't understand the BBC's logic - on their national forecasts they always put the min temps in the built up areas, so yesterday a huge temp symbol over London said -1c, which also covered my area, whereas I have no doubt most areas outside London saw temps as low as -5/6c. I'm in Hertfordshire but that temp symbol was the nearest to me, and it got down to -5c.

I'm sure the city folk wouldn't mind if the temperature was put as minimum for the region rather than just the built up areas.

Edited December 19, 2009 by Tommyd1258

[kold weather]

Even out at +165, this 06z run is very similar to the 00z. Two runs in a row showing a deep low tracking over France and somewhat stalling over the UK, before a beast of a low in the Atlantic rears its ugly head for the last week of the decade.

Yep but how many times have we seen the GFS makes a beast of a low only to have it end yp far weaker...I'm fully expecting the GFS idea of a 975mb low over the UK to be slowly weakened, if the set-up happens then the UKMO will be closer to the mark I'd have thought but we shall see!

[Lettucing Gutted]

I was just thinking this myself John. The GFS was predicting maximums of -2 or -1c across large swathes of central England earlier in the week, here it is still -4c, so there is more proof that the GFS doesn't always go insane with the minimums.

It seems to be spring and summer when the gfs has minimum and maximum temperatures below reality.

[SnowBallz]

Yep but how many times have we seen the GFS makes a beast of a low only to have it end yp far weaker...I'm fully expecting the GFS idea of a 975mb low over the UK to be slowly weakened, if the set-up happens then the UKMO will be closer to the mark I'd have thought but we shall see!

If they see that one of the models always overdoes the strength of a low (or whatever) then can't they compensate for it in other runs? Or does it not work like that? (soz, im trying to learn)

[TEITS]

Its interesting to see, courtesy of Wx Online how cold last night was after the discussions about GFS showing values too low.

Topcliffe (28 m)-13° Dishforth (33 m)-10° Birmingham (99 m)-9° Benson (57 m)-9° Cottesmore (142 m)-9° Tees-Side (37 m)-9° Sennybridge (307 m)-9° Shap (249 m)-9° Linton-On-Ouse (14 m)-9°

so two places already had -10C or below.

I'll wager there will be more over the next 2-3 nights?

Indeed John and I have often debated the GFS temps predictions with Stephen Prudence who was very dismissive of the GFS. I said at the time the temp predictions were plausible and that proved to be the case.

Speaking of temps but something very strange occuring in Peterborough. At 9am it was -3C but by 10am its dropped to -6C. This is an official weather station by the way based in RAF Wittering. I am somewhat confused how the temps can drop this much at this time of day.

[Matt12]

If I'm honest, the indications today are that the South will become milder by Christmas eve/Christmas day, with the Northern half of the UK staying cold until about the 27th or 28th, when the milder air will reach there as well. If I were to make a forecast at this stage it would be:-

Southern half of England - temperatures increase to around 4 or 5 degrees on Christmas day, with quite a bit of rain around. Temperatures, at this stage, look set to stay pretty average (4-8 C) until at least early January, although this is far from certain.

Northern half of the UK - Cold, with plenty of snow around until about the 27th/28th of December, when the milder air arrives. Temperatures will then recover.

In summary, I think the chances of the Northern half of the UK seeing a white Christmas is high, but it looks increasingly unlikely in the South. Temperatures will recover before the New year.

Matt.

[Frosty.]

If I'm honest, the indications today are that the South will become milder by Christmas eve/Christmas day, with the Northern half of the UK staying cold until about the 27th or 28th, when the milder air will reach there as well. If I were to make a forecast at this stage it would be:-

Southern half of England - temperatures increase to around 4 or 5 degrees on Christmas day, with quite a bit of rain around. Temperatures, at this stage, look set to stay pretty average (4-8 C) until at least early January, although this is far from certain.

Northern half of the UK - Cold, with plenty of snow around until about the 27th/28th of December, when the milder air arrives. Temperatures will then recover.

In summary, I think the chances of the Northern half of the UK seeing a white Christmas is high, but it looks increasingly unlikely in the South. Temperatures will recover before the New year.

Matt.

Unless the ecm output proves more accurate, in which case it remains either cold or very cold with snow at times and frosty nights.

[BLAST FROM THE PAST]

As regards to the models and the outlook, a few markers I used to look at to assess a breakdown etc were..where is the angle of attack from milder weather coming from. The SSW approaches....and how far north does it get. Well thus far an attempted breakdown from the SW or SSW is IMO a good sign for either prolonging the cold or setting up a re-load down the line. Why? well as we see from the GFS 06z for example is that the LP on 22/3 gets sent up clipping the SE corner, can't post it for some reason but look at T81 and look at the HP to our far NW extending way down into the Atlantic. This maintains cold air to the W and NW of the UK and Ireland signalling that the Atlantic isn't in control [otherwise we'd see an LP barrelling in from our NW and cold air shunted back to Russia]. This also means that mild doesn't push the cold way away to the far NE of Europe, it shows that the jet remains on a more southerly track and a chance of cold remaining and/or re-loading is somewhat strengthened.

Even though I love cold and snow and I live in the SE I'd take the current charts for it will still be cold and some very interesting weather too nonetheless

BFTP

Edited December 19, 2009 by BLAST FROM THE PAST

[Thundery wintry showers]

Christmas Day itself is still very much up in the air. I agree with Frosty that the ECMWF output would keep things pretty cold and snowy out to Christmas even in the south- and bear in mind that the ECMWF is less prone to going "off on one" than the GFS. UKMO and GFS outputs would see things turn milder from the south, so that is another option, but about half of the GEFS ensembles support the ECM.

So chances of a white Christmas, for me, continue to stand at 70% in central & northern Scotland, falling to nearer 30% southern England, I am hoping that we see the models fall into line with ECM so that those percentage ratings in the south in particular can increase.

Before that, still looks like remaining cold & snowy out to 23 December. The upcoming front may have rain and sleet on its forward edge but the warm pool of air coincides only with the forward edge, so other than that it should fall as snow.

[Matt12]

Christmas Day itself is still very much up in the air. I agree with Frosty that the ECMWF output would keep things pretty cold and snowy out to Christmas even in the south- and bear in mind that the ECMWF is less prone to going "off on one" than the GFS. UKMO and GFS outputs would see things turn milder from the south, so that is another option, but about half of the GEFS ensembles support the ECM.

So chances of a white Christmas, for me, continue to stand at 70% in central & northern Scotland, falling to nearer 30% southern England, I am hoping that we see the models fall into line with ECM so that those percentage ratings in the south in particular can increase.

Before that, still looks like remaining cold & snowy out to 23 December. The upcoming front may have rain and sleet on its forward edge but the warm pool of air coincides only with the forward edge, so other than that it should fall as snow.

Yep, I pretty much agree with all of this. It's also worth bearing in mind - which I didn't really express in my previous post - that it's impossible to make particularly accurate forecasts of Christmas day at the present time when it's so far away, and there is such a diverse range of outputs for anything beyond the next 3 or 4 days.

Edited December 19, 2009 by Matt12

[casparjack]

Indeed John and I have often debated the GFS temps predictions with Stephen Prudence who was very dismissive of the GFS. I said at the time the temp predictions were plausible and that proved to be the case.

Speaking of temps but something very strange occuring in Peterborough. At 9am it was -3C but by 10am its dropped to -6C. This is an official weather station by the way based in RAF Wittering. I am somewhat confused how the temps can drop this much at this time of day.

I agree, seems very odd, is there any fog in the area, that would seem to be the only potential explanation?

[kippure]

Where would i get an up to date veiw of the 850,s from the 1st of febuary to 7th of march 1947. I can view the charts here on NW in the archive section, but has anyone brought them into the way we see the charts nowadays.

Edited December 19, 2009 by kippure

[Frosty.]

Just seen the latest meto update and it suggests to me a blend of the ecm 00z and gfs 06z with some encroachment of less cold or dare I say milder air into the south later next week but never getting very far north before colder air pushes back down from the north or northwest across all areas later. The good news is, any mild/less cold advance will increase the chances of persistent precipitation which would be of snow on the northern side of the front but impossible to say where the battleground would take place.

Edited December 19, 2009 by Frosty039

[casparjack]

Just seen the latest meto update and it suggests to me a blend of the ecm 00z and gfs 06z with some encroachment of less cold or dare I say milder air into the south later next week but never getting very far north before colder air pushes back down from the north or northwest across all areas later. The good news is, any mild/less cold advance will increase the chances of persistent precipitation which would be of snow on the northern side of the front but impossible to say where the battleground would take place.

It looks to me like a complete blend, taking the trend shown on ECM to go with cold overall, but allowing for the GFS indication of some mild encroachment so as to 'hedge' their bets.

Overall I feel that the colder scenario will prevail, though as many have said on here there will be an element of mixing out at the edges, but as we all know and keep saying, well established surface cold is difficult to shift, especially when there is an absence of a really strong push from the Atlantic to introduce a pattern change.

[Cumulonimbus Tower]

I agree, seems very odd, is there any fog in the area, that would seem to be the only potential explanation?

A similar thing happened at Bingley yesterday morning. The temp was rising from about -2.7 to -2.3 then at ten o'clock it went back down to below -3

[johnholmes]

latest 12z chart showing the front and areas of snow on and behind it along with a sat picc from Dundee-usually would use NW but this is perhaps better today.

It looks to me like a complete blend, taking the trend shown on ECM to go with cold overall, but allowing for the GFS indication of some mild encroachment so as to 'hedge' their bets.

Overall I feel that the colder scenario will prevail, though as many have said on here there will be an element of mixing out at the edges, but as we all know and keep saying, well established surface cold is difficult to shift, especially when there is an absence of a really strong push from the Atlantic to introduce a pattern change.

I have posted many times on here that UK Met use ALL models, EC, GFS their own and various short and longer term specialist models of their own-rarely is one taken on its own.

[Frosty.]

It looks to me like a complete blend, taking the trend shown on ECM to go with cold overall, but allowing for the GFS indication of some mild encroachment so as to 'hedge' their bets.

Overall I feel that the colder scenario will prevail, though as many have said on here there will be an element of mixing out at the edges, but as we all know and keep saying, well established surface cold is difficult to shift, especially when there is an absence of a really strong push from the Atlantic to introduce a pattern change.

Agreed, much more weighted towards the ECM 00z, just hope we don't see any significant downgrades from the 12z ecm now, i'm almost sure the gfs will continue to show a less cold trend from late next week but i'm hoping it doesn't of course.