12z Model discussion - rain, sleet or snow?

[Paul]

Please continue discussion on the latest model runs here - please stay on topic. General cold spell discussion is available in this thread:

http://www.netweather.tv/forum/index.php?showtopic=36157

In depth/techie model discussion is here:

http://www.netweather.tv/forum/index.php?showtopic=34546

The latest GFS models can be seen here:

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

And the ensembles here:

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

Plus all the other major models and other features in the datacentre (free):

http://www.netweather.tv/index.cgi?action=charts;type=home

[R.P. McMurphy]

I would dismiss most of the strange comments of it's "a southerly event"...Notice the people saying that come from the "South"...Does not take a genius to work it out. Some people on here are really straw clutching.

IMO, what will happen is any snow/sleet will turn to rain down south, Bristol upwards, sleet/snow possibly turning back to rain the more south you are. Any further, Midlands north, with showers penetrating yorkshire, durham etc. Snow NOT turning to rain Midlands Northwards.

[kold weather]

Agreed Glenn its certainly not just a southerly event, by no means i suspect most parts of England+Wales have a real shot at snow. The main debate on here however is will it get as far north as the GFS expects, because the Fax charts only has the front just reaching the Midlands in the first placeand this is where the models and the uncertainty has to increase:

http://www.wetterzentrale.de/pics/brack2a.gif

This also has good agreement from a couple of higher resolution models as well as the GME, the GEM is actually so far soth it nearly misses the south of England!

12z coming out right now, low is if anythign a touch further north on the 12z, tohugh ion truth that may be just because its a touch stronger as you'd expect given the 12z usually has a slightly stronger lp's then the 06z runs.

[multi cellular thunderstorm]

The low already looks quite different in shape and slightly further north.

It also isn't as deep on this run, could that be bad?

[Supercell]

The GFS 12 hrs zoom charts show the -5 850 temps moving away from south western areas more rapidly than the 06z. An early scare ?

Edit - Just a wild fluctuation !

[Joneseye]

I would dismiss most of the strange comments of it's "a southerly event"...Notice the people saying that come from the "South"...Does not take a genius to work it out. Some people on here are really straw clutching.

IMO, what will happen is any snow/sleet will turn to rain down south, Bristol upwards, sleet/snow possibly turning back to rain the more south you are. Any further, Midlands north, with showers penetrating yorkshire, durham etc. Snow NOT turning to rain Midlands Northwards.

I get the impression that those people haven't even looked at the models over the last few days.. the main problem is the lack of consistency between from the models even at this short range. I guess a lot of this stems from the lack of these synoptics over the last few years, but it doesn't help when the models cannot.. erm.. model things accurately (for the want of a better phrase!?)

As for your second point that will again depend on the exact track of the low pressure, what time it arrives, the dew points, the intensity of the precip etc. .. obviously overnight arrival is more beneficial as well due to the lower temps..

Anyway fun watching and beats work any day of the week..

[pooksly]

Looking at the snow forecast charts it seems to still be rain for the south

[The Eagle]

I think the GFS has this nailed tbh. I dont think the UKMO has this right. I suppose we will see later. Both the GFS and ECM seem in agreement at 48hrs. You would have to favour them. The consistency now on the GFS is good.

[Jude_foster]

Looking at the snow forecast charts it seems to still be rain for the south

south of the M4 yes

[shrike]

I would have to say Wales and parts of Southern Ireland would be the favoured spots at the minute for heavy snow

[kold weather]

Hmmm, but the UKMO and most importantly its fax charts don't agree and I'd much favor the fax charts over any other model, at least at this sort of time-range.

There really isn't that much difference mind you however the KEY is the angle that the fronts come in at. The GFS has a clear tilt to the front as the positive advecation charts show quite nicely:

(the reds will be the front in this case.)

http://www.wetterzentrale.de/pics/Rmgfs397.gif

While the fax charts show obviously a more W-E orientation to the front:

http://www.wetterzentrale.de/pics/brack1a.gif

Remember also Darkman, in these set-ups, consitancy doesn't mean its right!!!

Saying that I agree wit hthe idea that has been thrown aobut here, snow to rain in the south (BUT the snow will last quite a lot longer then the GFS progs right now) and somewhere in the Midland region and N.Wales could well be hit rather hard I'd guess.

[pottyprof]

Some decent precipitation for mid day Thursday..

This from NW Extra

[PB22]

12Z GFS showing signs of becoming less progressive over the upcoming 66 hours or so.

[The Eagle]

Hmmm, but the UKMO and most importantly its fax charts don't agree and I'd much favor the fax charts over any other model, at least at this sort of time-range.

There really isn't that much difference mind you however the KEY is the angle that the fronts come in at. The GFS has a clear tilt to the front as the positive advecation lobes show quite nicely:

http://www.wetterzentrale.de/pics/Rmgfs397.gif

While the fax charts show obviously a more W-E orientation to the front:

http://www.wetterzentrale.de/pics/brack1a.gif

Remember also Darkman, in these set-ups, consitancy doesn't mean its right!!!

Saying that I agree wit hthe idea that has been thrown aobut here, snow to rain in the south (BUT the snow will last quite a lot longer then the GFS progs right now) and somewhere in the Midland region and N.Wales could well be hit rather hard I'd guess.

Yes KW, I I wish ppl would take this into account. It often happens in situations like this that the snow is meant to turn to rain but from my experience - once it starts snowing it usually just continues until the front clears through. Im sure you know what I mean.

Hi Shrike not too bad for NI either mind you

[Jude_foster]

A repeat at +84 ?????

[Thundery wintry showers]

-->

QUOTE(Paul B @ 6 Feb 2007, 04:00 PM) <{POST_SNAPBACK}>

12Z GFS showing signs of becoming less progressive over the upcoming 66 hours or so.

Agree; looks like greater chances of the block to the E holding for longer on this run.

[Nick F]

Not sure GFS has the low track nailed yet for Thursday by any means, particularly as it's resolution is not so defined to where the centre of the developing low will be, as where it forms beneath the upper trough moving East across the South will determine the flow at the surface and ultimately the fine line between rain and snow, GFS isn't great at picking up these mesoscale features with it's resolution IMO.

Interesting that in the wake of Thursdays low moving ENE, colder sub -5C returns SW across the East on Friday:

[PB22]

A repeat at +84 ?????

Beginning to look like it possibly. GFS may be coming round to the idea that the blocking to the northeast will play more of a role than it has predicted it to do so so far.

[memories of 63]

Is there also early height rises over North Uk/Scandi and spreading back into Greenland?

[SMU]

T 78 & the GFS is moving towards the GEM....

There could be a BIG round 2....

S

[kold weather]

wow, thats a stunning set-up:

http://www.wetterzentrale.de/pics/Rtavn841.png

Importantly it follows a similar evolution to the 0z UKMO run and tohugh a little different in regards to Thursday it follows up with colder air digging in back from the east before another deep deep low comes in from the west, how intresting would that be. also note how close it is to GEm, if that Lp was weaker then it would be very similar.

(ps, Nick I agree, though even the higher reoslution models I've seen are fairly split which is quite uncommon, i think this is why so many people are mentioning about the chances of it being further south, tohugh this can also apply for the system being further north, though usually in these set-ups the models weaken high pressure too quickly, which if you apply it the other way round to normal then the front may well have a very hard time getting in...but on the 12zx run the cold actually winds, wow!

[Glacier Point]

2nd phaser looks like arriving just at the right time with a cold night Saturday over the snow fields with plenty of ppn to the SW:

http://www.wetterzentrale.de/pics/Rtavn842.html

http://www.wetterzentrale.de/pics/Rtavn844.html

http://www.wetterzentrale.de/pics/Rtavn8417.html

and I would suggest this is also subject to possible upgrades..

[shuggee]

Very interesting run indeed for Fri into Sat for Scotland for snow. And for the whole of the northern half of the UK - biting gale force SE'lies.... *shudder*

[SMU]

Ramp alert everyone is now finally buying onto the idea of the second shortwave evolution.....

Nice to see you posting again PB......

S

[Jude_foster]

Deja - vu Anyone?