Model Output - General Discussion

[kold weather]

Wednesday now also a very cold day on the 12z run, Thursday sees a shortwave develop and pull southwards across the SE which should help tilt the winds slightly ENE. Much closer to the Euros on the 12z thus far, though general bigger evolution is similar to previous GFS runs.

[Paul]

As the posts start to increase again this pm with the 12z's coming in, please have a read of this thread regarding the 3 model discussions now running:

http://forum.netweather.tv/topic/58023-winter-topics-please-read/

We need everyone to ensure their posts are posted into the relevant threads please!

[kold weather]

Looking at the 12z - It seems to be gearing up for more energy in the southern stream- hence the lower heights to the East & a better flow- however its being VERY VERY progressive on the Greenland jet V the 06z

this will be a better run- but the cold cuts off to soon- due to the abive reason-

Steve

Yep, what it gives with one hand it takes with the other almost!

Saying that the pattern for the northerly shot afterwards is far better on this run, the low is quite a good deal further west at 120hrs and stronger thanks to the more progressive jet, plus there is barely a warm sector at all!

Still, would be nice for it to be just a little slower and in truth it probably will be slower as the 12z GFS runs tend to be the most progressive of all.

[Lewis]

Fantastic 12z upto now, a certain upgrade.

Before the easterly shunts out the way and colder air we already have the potent Northerly knocking on the doors of Scotland. Could the 2 air mass's collide and cause more instability, or is that not physically possible.

Lewis

[Harsh Climate]

This run is marginally better than the 06z, but not good enough in terms of following the ecm. I expect to see the ecm backtrack later but hope im wrong.

[SMU]

Wednesday now also a very cold day on the 12z run, Thursday sees a shortwave develop and pull southwards across the SE which should help tilt the winds slightly ENE. Much closer to the Euros on the 12z thus far, though general bigger evolution is similar to previous GFS runs.

Snow moving down from the North at 126- however watch that round low over Portugal beginning to swing up-

By the shape & profile of things that shirt skirt our southern flank-

http://91.121.94.83/modeles/gfs/run/gfsnh-0-132.png?12

S

[Iceberg]

Yep, what it gives with one hand it takes with the other almost!

Saying that the pattern for the northerly shot afterwards is far better on this run, the low is quite a good deal further west at 120hrs and stronger thanks to the more progressive jet, plus there is barely a warm sector at all!

Still, would be nice for it to be just a little slower and in truth it probably will be slower as the 12z GFS runs tend to be the most progressive of all.

Yes this is a case of the 12Z trying to bridge the gap with the Euro's and it's done it nearly maybe 70%.

No real warm sectors now as you say on Wed, nor before the northerly.

[Optimus Prime]

Fantastic 12z upto now, a certain upgrade.

Before the easterly shunts out the way and colder air we already have the potent Northerly knocking on the doors of Scotland. Could the 2 air mass's collide and cause more instability, or is that not physically possible.

Lewis

Nope you can't have that happen. They'll always be an area of divergence where the warm sector is.

Edited December 13, 2009 by Optimus Prime

[Neilsouth]

Steve what's the cause in the models which gives the stronger east/north easterly on the ecm/ukmo over the gfs?. Do you think it will side more with the euros?

[Duncan McAlister]

Good to see the Continent so cold so early in the season as well as our own cold spell.

[Backtrack]

Yes this is a case of the 12Z trying to bridge the gap with the Euro's and it's done it nearly maybe 70%.

No real warm sectors now as you say on Wed, nor before the northerly.

I think there will be one warm sector. With every cold spell comes a warm sector. Last feb saw a similar setup. Brought me a foot of snow only to melt overnight due to a warm sector.

[Harsh Climate]

which defies logic because the last two runs have seen the GFS tend towards the ECM NOT the other way round. So far this one is very much tending more to the ECM evolution, and I would imagine it to continue to do so over next couple of runs :blush:

sorry mate but the differences between gfs 12z and ecm 00z are HUGE

Heres what the models show at 120h

gfs

http://www.wetterzentrale.de/pics/Rtavn1201.png

ecm

http://www.wetterzentrale.de/pics/Recm1201.gif

In terms of the gfs 12z uprgrading the easterly into something like the ecm, no where near. Im interested to see how the gfs 12z handles anysort of breakdown. Hopefully no breakdown!

Edited December 13, 2009 by Jed Bickerdike

[Iceberg]

I think the GFS 12 Z has forgot about the warm sector a kink very quickly forms in the northerly and all snow lets lose, nobody in scotland should be unhappy with this inside 144Z, (Follows down into England and wales nicely as well ! )

[Thundery wintry showers]

Indeed there is usually a pool of warmer air associated with a frontal snow event- it can be, literally, a "warm sector" (a region of warmer air between a warm front and a cold one) or modified air from within a depression core. Such pools of warmer air can nonetheless give rise to snow events if they are not pronounced enough to raise temperatures to the warm side of marginal.

The same is not generally true of snow showers generated over the sea.

If the UKMO/ECM start to backtrack on today's 12Z runs then I will suggest that something similar to what GFS is showing, or maybe toned up very slightly, will be the most likely outcome. If not, then I will expect the GFS to fall into line with the Euro models by tomorrow morning, as the recent trend has been in the direction of the impressive ECM outputs.

[Neilsouth]

I think there will be one warm sector. With every cold spell comes a warm sector. Last feb saw a similar setup. Brought me a foot of snow only to melt overnight due to a warm sector.

There is always a warm sector , but the depth of the warm setor is under question. Sometimes it's enough to turn snow to rain but not always :blush:. I don't think it's worth looking at the warm sector till nearer the time

Oh and Worzel

Worzel - get some cider in side her. , can you put that in your signature and not at the end of every post?? , THANKS

[cooling climate]

It will be interesting to see if the Euro's have toned down the easterly at all this evening but as far as

the evolution of the cold / very cold spell goes the GFS has almost completely come aboard with the

ECM by t144.

This should be a better run than the 06z for longevity of the cold spell we shall see.

[Eugene]

http://www.wetterzentrale.de/pics/Rtavn1441.png - POLAR LOW.

Wow amazing GFS 12Z, that would give a pasting to northern britain :blush:

[Optimus Prime]

Worzel - get some cider in side her.

I agree. This run also progresses height rises over Scandinavia and Siberia from Saturday. Could give some cold weather still for the Christmas period for those who want it.

[Tom D]

Quite a considerable change at +150 compared to the 06z, with the polar lows flying down much sooner keeping the Atlantic lows at bay. Definitely potential for some snow in this scenario, with a northerly set up.

[Iceberg]

I am not sure I would want it to be any different TWS, this is quite a snowy run.

Maybe a little more on Thursday would be nice, but I feel I am really pushing my luck.

A second low forms further west, keeping the cold and snow going as we enter FI.

[i luv snow]

sorry mate but the differences between gfs 12z and ecm 00z are HUGE

Heres what the models show at 120h

gfs

http://www.wetterzen...s/Rtavn1201.png

ecm

http://www.wetterzen...cs/Recm1201.gif

In terms of the gfs 12z uprgrading the easterly into something like the ecm, no where near. Im interested to see how the gfs 12z handles anysort of breakdown. Hopefully no breakdown!

point taken, but I used the word TENDING not upgrade or matching for a purpose - its going the right way and Im sure there will be a few changes yet

Edited December 13, 2009 by i luv snow

[Turnedoutniceagain]

Quite a considerable change at +150 compared to the 06z, with the polar lows flying down much sooner keeping the Atlantic lows at bay. Definitely potential for some snow in this scenario, with a northerly set up.

Beat me to it !! Some proper cold arriving on the continent also.

It's all about trends........and they're going the right way. Good Scandi height rises popping up now.

[kold weather]

GFS also still taking longer to really decrease heights over Greenland region, this is a trend that I really think will become more and more obvious over the next few runs.

Anyway a very cold run yet again, a much better run for westerners so far as the low swings down from the Arctic somewhat quicker putting the UK into the colder air at the first time of asking, something which the 06z fails at doing.

[Thundery wintry showers]

Yes, the longer-term GFS output is an excellent illustration of how those cyclonic northerly regimes, as opposed to tame 36-hour topplers, can actually be every bit as effective at giving widespread snow events as a full-on easterly.

[Alex95]

http://www.wetterzentrale.de/pics/Rtavn1441.png - POLAR LOW.

Wow amazing GFS 12Z, that would give a pasting to northern britain

That is the best northerly scenario you can get around here, last really good polar low was Christmas 1995, can't remember it myself as I was to little but I'm aware 10-15cm fell. IMO the key to how strong the easterly is later on this week will be how large the short wave is. If it is weak the high will topple like the GFS has been showing us, if it is bigger like it the METO model the high could get propped up, giving a more prolonged easterly. If the easterly topples a northerly will probably follow.