Model Output General Discussion

[bluearmy]

i means that we look at their site for longer, making them feel a little more important

they are both the same now. i doubt the 18z will update. the 12z op and parallel output were identical on meteociel.

[Thundery wintry showers]

Aye, I know a lot of people were saying they would bank the 12Z but if I could bank a run it would definitely have to be the 18Z. Amazing stuff, a proper cold wintry spell, and the breakdown hangs about until the other side of Christmas.

What looks unlikely to me in this run is the low slipping south at around T+168 allowing in that easterly flow and pressure building to the north. Ultimately if we are to get a cold spell lasting beyond Christmas we will need some kind of general pressure rise to the north holding off the Atlantic systems, but I think today's ECMWF runs (both 00Z and 12Z) are a more plausible way of facilitating this. Christmas Day is still, obviously, FI at this range.

[Barb]

Christmas eve/day blizzard anyone?

[Snowly does it]

By T336, the cold is so entrenched that there would be a severe blizzard brewing as the LPs try to undercut the cold HP cell above Scotland.

This is an exceptionally cold run showing just how difficult entrenched cold and favourable heights to the NW could be to shift.

Textbook old school etc.

[benb]

Another absolute stormer from the 18z and another possible mid-term solution!

Generally, the GFS has been spot on in the run up to this cold spell for well over a week now: weak easterly then cold easterly. Let's hope the switch to the northerly has been as well modelled!

[casparjack]

Personally I feel some of these very low temp predictions by the GFS are perfectly plausible. The combination of clear skies, light winds, arctic airmass, lying snow can easily cause min temps to drop very low. Due to the short daylight hrs the temps struggle to rise very much which is why you see such low max temps. Happened in 1981 and no reason why it can't happen again!

I agree, but I'm not convinced that we'll see sufficiently clear skies and slack winds will we, I'm struggling for the chart, I'll post it in a sec. Not being negative, I love extremes, that's my my whole interest in meteorology.

[Snowly does it]

the Atlantic finally gets back in for round about New Year, amazing run!

Would surely produce a 16 day spell of sub-zero temps if it were to pan out like that and would be, by a country mile, the best spell of cold weather since the 80s.

I admit to a little giddy excitement which I am prepared to permit myself just this once!

[TEITS]

What I find encouraging is some model runs are reluctant to bring a return to milder weather. Now when you consider normally the models are far too progressive in bringing an end to the cold spell, the fact that in F.I there is the reluctancy is very encouraging.

[Yeti]

Amazing, then a "Hogmonay blizzard" to finish!

http://www.wetterzentrale.de/pics/Rtavn3721.png

Incredibly snowy run, that would be 1947 equivalent in terms of depth of snow and severity of cold!

FI

[Upgrade]

What I find encouraging is some model runs are reluctant to bring a return to milder weather. Now when you consider normally the models are far too progressive in bringing an end to the cold spell, the fact that in F.I there is the reluctancy is very encouraging.

that's right and there's quite a lot of consitency in these delays - and now attempts to raise pressure to the north, and rebuild the easterly, over repeated runs. it could turn out even better than expected ( rare we say that with any confidence)

[SP1986]

I am sorry but the temperature shown by the GFS are nothing short of ridiculous, there must be a glitch in the system, because there is no way the temperature would drop 4-5C from 12pm to 3pm, and then drop severely to -15C overnight. It's verging on climatically impossible for an island in the Atlantic!

It will have changed by tomorrow, but some shockingly bizarre specific output by the GFS. If there ever was a true pub run, it's this one.

[Geordiesnow]

What I find encouraging is some model runs are reluctant to bring a return to milder weather. Now when you consider normally the models are far too progressive in bringing an end to the cold spell, the fact that in F.I there is the reluctancy is very encouraging.

Yep it is encuraging the models are still showing very little sign of any breakdowns regarding the Atlantic. This run is perfect in bringing that low down as that can only help us in keeping the cold air over us and of course alot more PPN.

Got to bear in mind the UKMO however and just because the models today have been generally good does not mean tomorrow morningwe will come down with a bump.

Anyways at least 5 days of cold weather is nearly upon us now so we may aswell enjoy it whilst we can.

[snowlover2009]

What I find encouraging is some model runs are reluctant to bring a return to milder weather. Now when you consider normally the models are far too progressive in bringing an end to the cold spell, the fact that in F.I there is the reluctancy is very encouraging.

i agree and all the mild weather gets shifted further back all the time. take this gfs run for instacnce the very end starts to just get a bit milder. also it is very unusual for us to be still looking at so many good set ups of cold and snow etc for about 2 weeks on since this cold spell ws being hinted at, very unusual, only mild weather i have seen has been in deep fi and even barletts what have showed get knocked back further down the line. it has been almost 3 weeks now of seeing so many cold runs its pretty unbeliveable and encouraging.

[Rob]

I am sorry but the temperature shown by the GFS are nothing short of ridiculous, there must be a glitch in the system, because there is no way the temperature would drop 4-5C from 12pm to 3pm, and then drop severely to -15C overnight. It's verging on climatically impossible for an island in the Atlantic!

It will have changed by tomorrow, but some shockingly bizarre specific output by the GFS. If there ever was a true pub run, it's this one.

the 12z was showing similar, unusual for 2 runs to have glitches?

[TEITS]

I am sorry but the temperature shown by the GFS are nothing short of ridiculous, there must be a glitch in the system, because there is no way the temperature would drop 4-5C from 12pm to 3pm, and then drop severely to -15C overnight. It's verging on climatically impossible for an island in the Atlantic!

Which timeframe does the 18Z do this Stephen as I missed this?

[Thundery wintry showers]

I am sorry but the temperature shown by the GFS are nothing short of ridiculous, there must be a glitch in the system, because there is no way the temperature would drop 4-5C from 12pm to 3pm, and then drop severely to -15C overnight. It's verging on climatically impossible for an island in the Atlantic!

It will have changed by tomorrow, but some shockingly bizarre specific output by the GFS. If there ever was a true pub run, it's this one.

You should have seen the GFS 12Z then, which was projecting maxima of -2 to -5C over a wide area and minima of -10 to -12C over a wide area, all despite 850hPa values of -6 to -8C and a sluggish westerly flow.

I would expect temperatures like that to occur locally in such a setup (in fact I'm expecting some frost hollow in Scotland to drop below -20C at some point during the northerly), but not over most of the country. That would be right up there with the exceptional cold around 12 December 1981 and I don't think the charts quite support something of that intensity.

[Bartlett Low]

the 12z was showing similar, unusual for 2 runs to have glitches?

But its the new "parallel" GFS remember.

[Rob K]

http://www.wetterzentrale.de/pics/Rtavn18017.png

I agree with TEITS- Uppers become irrelevent in this type of situation-

Slack air

Snow cover

Entrenched cold at the surface-

-13c in that frame-

& yes I doubt ive ever seen -15C in high res....

http://www.wetterzentrale.de/pics/Rmgfs1804.gif

For people that are discounting these double-digit negative minima... remember we saw minima below -10C in southern England in January 2009 (at my local station, Farnborough, for one), and that was with no snow cover! I think the lowest recorded in that spell was -11.9C at Chesham, Bucks.

[cooling climate]

I think after looking at the 18z GFS you just couldn't get anything better. Its got everything that you could

ask for and would rank alongside any of the archive freeze ups, incredible run.

What the models are showing I think is once the very cold weather becomes imbedded over the weekend

and into next week the weather pattern will default to cold rather like when you are in the middle of a mild

or very mild spell the mild always seems to be the default pattern.

I hope that makes sense.

[TEITS]

Well it's happened in the past hasn't it? Didn't Shawbury or somewhere like that get sub -20c once?

I agree though, all of this will just be a distant memory by tomorrow morning.

Yes Shawbury during the 12-13th Dec. The temp dropped to -25C and was already -22C at 6pm on the 12th.

Here are the charts.

http://www.wetterzentrale.de/archive/ra/1981/Rrea00119811213.gif

http://www.wetterzentrale.de/archive/ra/1981/Rrea00219811213.gif

[paul tall]

I am sorry but the temperature shown by the GFS are nothing short of ridiculous, there must be a glitch in the system, because there is no way the temperature would drop 4-5C from 12pm to 3pm, and then drop severely to -15C overnight. It's verging on climatically impossible for an island in the Atlantic!

It will have changed by tomorrow, but some shockingly bizarre specific output by the GFS. If there ever was a true pub run, it's this one.

Stephen, it is -3 at 1200 on 22/12, -4 at 1500 on 22/12 and -15 at 0600 on 23/12 using the Pennines as an example. Where is the 4-5c drop between 12 and 1500? And over a snowfield in the right conditions is it that implausible for an afternoon temperature of -4 to drop to -15?

[Hairy Celt]

I'd just point out that we get the odd few runs like this every winter, maybe 3 or 4. Flashes of winter as it used to be, just that there's no real monster cold pool to the north to sustain it any more, more's the pity.

[SP1986]

Its not the figures I'm discounting as such, it's the areas there forecast to, and the way the temperature are changing.

For the temperature to be -2C at 12pm (fair enough), but then to drop to -5C by 3pm, anyone with experience in climate physics will know that on an island which is predominantly affected by the Atlantic ocean, this just doesn't happen!

If you think it's going to happen, good luck to you!

[SMU]

I am sorry but the temperature shown by the GFS are nothing short of ridiculous, there must be a glitch in the system, because there is no way the temperature would drop 4-5C from 12pm to 3pm, and then drop severely to -15C overnight. It's verging on climatically impossible for an island in the Atlantic!

It will have changed by tomorrow, but some shockingly bizarre specific output by the GFS. If there ever was a true pub run, it's this one.

Sorry Steve I think you are overeacting to the GFS output- IF the Synoptics varify as is then -15c is more than likely going to be smashed-

Newport in shropshire reached -26c in Jan 1982- I AM sure the GFS would have gone for a -15/-20 in that area on the high res model the day before..

we are just not used to these synoptics & reloads in the most recent past-

as regards your timings comments- Maybe 3-4pm.......

S

Edited December 15, 2009 by Steve Murr

[casparjack]

I agree, but I'm not convinced that we'll see sufficiently clear skies and slack winds will we, I'm struggling for the chart, I'll post it in a sec. Not being negative, I love extremes, that's my my whole interest in meteorology.

TEITS, here are the ones I had in mind, do you think we will see light winds and clear skies under these conditions - I hope so, but I'm sceptical.

The potential is there, I just think the set up will be too 'busy'.