Here is a summary of the NWP output for noon on Tuesday.
Issued 0600, 12th December 2008

The middle of the week looks wet, windy and (at times) mild as a deep area
of low pressure becomes established to the NW. All areas will see rain at
times, with snow largely restricted to the highest ground of the north.
Frosts will be less common than at present too.

Analysis and evolution to T+120 via GFS
A col covers England and Wales, with SW'lies elsewhere. Tomorrow a trough
moves eastwards, with strong to gale force southerlies in advance and
westerlies following behind. The trough disrupts on Sunday, with low
pressure over England. A col covers the UK on Monday.

T+120 synopsis
http://85.214.49.20/pics/Rtavn12014.png /
http://85.214.49.20/pics/Rtavn1201.png
http://85.214.49.20/pics/Rukm1201.gif
http://85.214.49.20/pics/Recm1201.gif /
http://www.meteociel.fr/modeles/nogapse_cartes.php
The jetstream chart shows a strong zonal flow over th North Atlantic, with
the jet heading northwards over the UK. At the 500hPa level there;s a WSW'ly
flow, while MetO has a SW'ly flow instead. ECM brings SW'lies aloft, while
GEM has WSW'lies.
At the surface, GFS shows a trough moving eastwards over England, with
southerlies in advance and WSW'lies following behind. MetO shows a similar
setup, while ECM brings SSW'lies across the UK. GEM also has SSW'lies,
albeit lighter than with ECM.

Evolution to T+168
Days 6 and 7 with ECM show SW'lies, with complex low pressure near Iceland.
Days 6 and 7 with GFS bring WSW'lies for all, again with a complex low near
Iceland.

Looking further afield
Days 8 and 9 with ECM show further SW'lies, as low pressure persists near
Iceland. Day 10 sees a trough to the west and southerlies for the UK.
Exceptionally mild SW'lies cover the UK on days 8 and 9 with GFS, as high
pressure builds to the south. By day 10 the high lies over northern France,
with westerlies across the UK.

Ensemble analysis
(http://91.121.94.83/modeles/gens/gra...ille=Lond res)
The ensembles still show a zonal outlook. The extended part of the run (post
T+180) was a marked warm outlier.

Christmas Countdown
**NOTE: The following section is provided on a "for fun" basis and is not to
be used operationally. Remember, temperatures can go down as well as up and
nothing is gauranteed when it comes to weather! **

http://91.121.93.17/pics/Rtavn3121.png
The operational GFS shows a high over southern Norway and Scotland, with
light winds for both Scotland and Northern Ireland. Elsewhere winds are
NE'lies. This would lead to a slight frost for many inland locations,
followed by a dry and sunny Christmas Day.

Ensemble wise, the members are split as follows:
SW'lies: 4
SE'lies: 2
Northerlies: 1
Southerlies: 3 (inc control)
NW'lies: 1
Easterlies: 6
Westerlies: 4

There's a surprising new leader of the pack today - easterlies. The ones on
the ensembles aren't especially cold, but the chance for lowland snow over
England and Wales is now higher than it was yesterday. Taken as an
aggregate, SW'lies or westerlies are still the most likely option. Taken at
face value, the ensembles suggest a SW'ly or WSW'ly flow (40% chance) or an
easterly flow (30% chance).