[South West/Central Southern England Regional Discussion 15/01/13 12z---->]

Re Ian F's talk of Met O thoughts basically turning to rain south of the M4... the raw five-dayers with very latest data (updated 0000 Jan 16) don't seem to back that up, e.g. my area shows no rain symbols at all, just light or heavy snow from Fri evening right through to Saturday.

But no doubt will all change several times before D-day!

[South West/Central Southern England Regional Discussion 15/01/13 12z---->]

is that not in mm ??

mm of rain is approx cm of snow...

[Winter Model Discussion 12Z 15/1/13 onwards.]

Cold enough for snow from direct westerlies in Ireland

http://www.wetterzentrale.de/pics/Rtavn1202.png

The world has gone mad!

[Winter Model Discussion 12Z 15/1/13 onwards.]

NAE is on a different page from the rest of the models.

http://expert-images...011718_1518.gif

Some head scratching going on at Exeter now I reckon

However looking at GFS, that is about as far as mild air gets in before being pushed back... then the main front arrives

http://www.wetterzentrale.de/pics/Rmgfs482.gif

to

http://www.wetterzentrale.de/pics/Rmgfs722.gif

[Winter Model Discussion 12Z 15/1/13 onwards.]

NAE still pushing the 0C isotherm in by T42.... has to be a concern! It might all push back if there is an undercut but already rain into the SW again

[The Winter emotions and moaning thread]

This gaves 8inches of snow in the midlands?

check out the 850's:

Thats tropical compared to Friday and Sundays 850's!!

To be fair colder air did move in during the event giving it a boost:

http://www.wetterzentrale.de/pics/archive/ra/1996/Rrea00219960207.gif

[Winter Model Discussion 12Z 15/1/13 onwards.]

Any news on the nae!!westward correction please!!

18Z run hasn't come out yet. Should be rolling out shortly...

[Winter Model Discussion 12Z 15/1/13 onwards.]

Question about the UKMO model - is it somehow lower resolution than GFS/ECM? I ask because the UKMO charts always seem to have very "clean", smooth isobars, compared to outher models.

E.g. see this link comparing ECM, UKMO and GFS side by side at 144hrs:

http://www.weatheronline.co.uk/cgi-bin/expertcharts?LANG=en&VAR=model_pslv&CONT=ukuk&MODELL=modens&BASE=-&MODELLTYP=1&VAR=model_pslv&WMO=&ZOOM=0&PANEL=0&ARCHIV=0&HH=144&modeladd=gfs&modeladd=ukmo&modeladd=ecmwf&modeladd=nae&submit=go

GFS in particular has shortwaves and troughs all over the place. ECM has little kinks here and there. UKMO just has a big round dartboard!

[Winter Model Discussion 12Z 15/1/13 onwards.]

Looks like a glitch

This is for the SW Midlands from Wetternzentrale - OP run is right in the midst of the ensembles

Kev's pic was a 2m temp ensemble rather than 850s. Only thing I can think is higher resolution vs the ensembles??

BTW a question for anyone who knows - does ECM model run at finer time intervals than the 24hrs we see?

[Winter Model Discussion 12Z 15/1/13 onwards.]

Quick question to Steve M or the other experts. am i right in thinking the charts for Friday and wkend are looking very similar to early Feb 96, which gave many western parts and the Midlands impressive snow depth 8 inches here in Brum. I seem to recall a low pressure system coming against a Scandi block then.

I don't claim to be an expert but yes this from Feb 1996 does have a lot of similarities if you compare to current output!

http://www.wetterzen...00119960206.gif

[Winter Model Discussion 12Z 15/1/13 onwards.]

Just going to post the JMA but some members came to the wrong conclusion about the 12Z NAE.

As you can see at +48 the JMA is like the NAE.

http://www.wetterzen...ics/Rjma482.gif

Look what happens though at +72 when the front pivots.

The cold backs W. However SW England/S Wales would miss out.

http://www.wetterzen...ics/Rjma722.gif

II take your point but the NAE is much more progressive with the mild sector than JMA. NAE has 0C into mid Wales at 48hrs; JMA keeps it out in Ireland

[Winter Model Discussion 12Z 15/1/13 onwards.]

Epic http://www.wetterzen...s/Rtavn1561.png, and whilst it is FI it is not deep fi!! I think this will be the broad evolution that apart from the fact i think everything will be 250miles further south, im getting excited yet concerned at the same time here, i love snow but i still want to get to work. I dont think ukmo at 144 is quite as good though

Maybe not as good but not mild by any stretch. 526dam in London, 523dam in Birmingham even as the low rolls in at 144hrs.

[Winter Model Discussion 12Z 15/1/13 onwards.]

However - the potentially errant 12z NAE prog for Thurs is a possible major spoiler and albeit we have it discounted for now..... watch this space. Fri considered 'low probability, severe impact' event currently and we need greater continuity through next 24hrs.

Ian how is the NAE regarded? I was given to understand it is a high-res model just for Europe but how does it compare with the "secret" Met Office models?

[Winter Model Discussion 12Z 15/1/13 onwards.]

A far better route to understanding (at least from GFS) the PPN type prospects for any given area, plus crucial nuances of boundary layer conditions as well as aloft, is to pick-up on the profile soundings plotted for any part of the globe via the excellent http://ready.arl.noa...v/READYcmet.php (we compare these here to our UKMO-GM/NAE tephigrams).

Of course, Ian, but does the data the Met Office is working with also support a disruptive spell for much of the country on Friday and Saturday, as we are seeing in GFS, GME and raw UKMO output?

Edit: sorry just saw your previous post. Thanks.

[Winter Model Discussion 12Z 15/1/13 onwards.]

On GFS the -5C isotherm is actually heading WEST from Wales northwards as the front pivots! Lovely.

[Winter Model Discussion 12Z 15/1/13 onwards.]

If UKM GM and ECM follow this...I suspect so Nick..

Heavy snow into the SW (with a possible new depression ready to cut beneath the UK a day later)

.. a nice way to start the afternoon's runs...

Bloody hell that's a blinder!

FWIW the 850s are 4C lower over Wales on GME at T+48 than on the NAE. Major major model disagreement.

[Winter Model Discussion 12Z 15/1/13 onwards.]

Chilly maybe but NAE has the 0C isotherm well into wales by T+48!

http://expert-images.weatheronline.co.uk/daten/proficharts/en/nae/2013/01/15/basis12/ukuk/t850/13011712_1512.gif

That is well ahead of even the supposedly progressive GFS 06Z!

[South West/Central Southern England Regional Discussion 15/01/13 12z---->]

Wouldn't be a damper if I could share 4-5d modified UKMO-GM output & MOGREPS with them.. ! ;-)

Ian you tease...

[South West/Central Southern England Regional Discussion 15/01/13 12z---->]

I was down Weymouth on 18th Feb 78 visiting family, The wind was bitterly cold coming off the sea blowing sand along Esplanade, On that evening rain started falling about 6,30 but changed to heavy snow, By midnight had changed back to rain, but the depth of snow along Weymouth seafront was phenomenal, But your point that cold was much more entrenched that year is true,

Looking at the archive charts it looks more marginal back then, with the 0C isotherm into the SW

http://www.wetterzentrale.de/pics/archive/ra/1978/Rrea00219780218.gif

[Winter Model Discussion 12Z 15/1/13 onwards.]

A rare post from me. A question for the knowledgeable:

The Met Office have a snow warning for Friday in the south west:-

http://www.metoffice...ings.html?day=4

but the fax chart for 96 hours does not show this as far as I can tell.

http://www.netweathe...s;type=fax;sess=

Where am I going wrong?

Many thanks,

Mike.

Not sure what you mean? The fax chart at 96hr as drawn is about as classic a "SW frontal snow" chart as you could get. If it happens like that of course, which is highly unlikely! Why do you think it isn't? SE winds, an occluded front heading into cold air and the trough disrupting and sliding under the block up the Channel!

However that chart has since been replaced by the 84hr chart (look at the forecast time, it is the same), which to my eye is much less favourable - it shows more of a straight-on attack rather than an undercut, although the trough is doing its best to disrupt. Also the cold air makes less inroads west, looking at the 528dam line.

Bear in mind that in this set-up, the 528dam line is not too critical.

[Model Mayhem - Moan, Ramp, Go Nuts]

Brady - we need deep entrenced cold across the UK to stand any chance of snow from an atlantic front - and we just aint got it.

Just as well then that there are still three days before the front moves in to get the cold in from the east then! Much of central Britain will stay below freezing day and night from tonight until Friday at least, based on current output.

[How Did The Models Perform?]

Yes I am surprised GFS performed best - must be an artifact of the time chosen. As I recall, GFS was totally out on its own with not sending the weekend shortwave SE over the UK, and instead wanted to send it NE to Svalbard. It was consistent for several runs in a row before caving in.

[Winter Model Discussion 12Z 15/1/13 onwards.]

The charts for next week are looking very similar to January 1984.

Compare:

with

That month was very snowy in the north, especially Scotland with 2ft of level snow in places, but only 1 day of lying snow in London. Read about it here:

http://www.personal.dundee.ac.uk/~taharley/1984_weather.htm

[Winter Model Discussion 18Z 13/1/13 onwards.]

GFS Ensemble mean at 144 looks rather like UKMO too.

http://www.meteociel.fr/modeles/gefs_cartes.php?code=21&ech=144&mode=0&carte=0

Undercutting looks the new favourite!

[Winter Model Discussion 18Z 13/1/13 onwards.]

Sorry guys I'm confused. To me the undercut looks like the atlantic powering back in from the west. How is this a good output? Just don't get it!

If the block holds firm to the north then the UK is on the northern side of the incoming low, forcing cold easterlies or south easterlies across us. If the lows go over the top of a sinking high, we are in the southern side of the low and get milder westerlies.

Undercutting Atlantic lows are as rare as hen's teeth but are responsible for many of the biggest UK blizzards of the past.