Here is a summary of the NWP output for noon on Sunday.
Issued 0525, 16th December 2009.

An area of low pressure will cold air entrained will become slow-moving over
Scotland during the first half of the week. A secondary low will move
swiftly ENE'wards over France and it's likely to bring less cold air across
the south as a result, with rain. Further north, there's the potential for a
fair amount of snow as the low slowly fills in situ.

Analysis and evolution to T+120 via GFS
England and Wales lie under a col, with light winds elsewhere. Tomorrow low
pressure moves over southern and SE ENgland, with increasingly cold NE'lies
elsewhere. Friday sees cold NE'lies for most, with less cold northerlies for
northern Scotland. NW'lies cover the UK on Saturday as a ridge moves
southwards.

T+120 synopsis
http://91.121.93.17/pics/Rtavn12015.png /
http://91.121.93.17/pics/Rtavn1201.png
http://91.121.93.17/pics/Rukm1201.gif
http://91.121.93.17/pics/Recm1201.gif /
http://www.meteociel.fr/modeles/nogapse_cartes.php
The jetstream chart continues to show a strong southerly branch of the jet
over northern Africa. A weaker secondary jet lies to the immediate south of
the UK. At the 500hPa level there's a deep upper low over the North Sea. ECM
has an upper low to the NE, as does MetO. GEM shows a trough to the east,
while JMA has an upper low to the north.
At the surface, GFS brings a low east of Scotland and strong NW'lies and
westerlies for the UK. ECM has westerlies for all with a low to the north
and MetO is similar. GEM shows NW'lies and a low to the east, while JMA
shows WSW'lies.

Evolution to T+168
ECM shows SW'lies on day 6 as a low moves over Scotland, followed by NE'lies
for many on day 7 as a secondary low deepens over France. Scotland remains
under northerlies.
A trough is moving southwards on day 6 with GFS, with SW'lies in advance and
northerlies following behind. On day 7 a low fills over Scotland, with
easterlies affecting the rest of the UK.

Looking further afield
ECM shows SW'lies for all on day 8 with a low to the north. SW'lies persist
on day 9, but by day 10 easterlies cover the UK ahead of a low to the SW.
Day 8 with GFS shows a deep low over the North Sea and strong northerlies
and NW'lies over the UK. A col covers the UK on day 9, followed by
easterlies and ENE'lies on day 10.

Ensemble analysis
(http://91.121.94.83/modeles/gens/gra...ille=Lond res)
After today, the majority of ensembles keep cold weather at the surface in
the south until Christmas.