Here is a summary of the NWP output for noon on Boxing Day.
Issued 0524, 22nd December 2009.

Sunday will see low pressure to the north and WSW'lies or SW'lies for most
of the UK. Rain is likely in the south, with any snow likely to be
restricted to higher ground from northern England northwards.

Analysis and evolution to T+120 via GFS
A slack low covers much of the UK, with a secondary low to the south and an
area of mild air over SE England. The low deepens over the North Sea
tomorrow, bringing northerlies for Scotland and WSW'lies elsewhere.
Christmas Eve sees southerlies and SE'lies from a low to the west, followed
by northerlies and NW'lies on Christmas Day as low pressure deepens over the
North Sea.

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 shows amplification in the Atlantic jet. The general
flow is still zonal and on a southerly track, but a secondary jet lies
closer to the UK, heading eastwards towards Cornwall and then veering
SE'wards over Biscay. The 500hPa chart shows upper westerlies, with the
northern and southern branches of the jet just to the south. ECM has a low
to the NW and upper SW'lies for the UK, as is the case with MetO. GEM brings
upper southerlies with a low to the west and JMA has a similar setup.
At the surface, GFS brings a low over the North Sea and a trough for the UK.
Winds are WSW'lies for England and Wales with NW'lies elsewhere. ECM has
SW'lies for all with a low to the NW, as is the case with MetO. GEM brings
southerlies and JMA has southerlies too, both with a low to the west.

Evolution to T+168
ECM shows WSW'lies on day 6 as a low moves ENE'wards. On day 7 a new low
approaches from the SW, with easterlies.
GFS brings a col for Scotland and Northern Ireland on day 6, with a ridge
and SE'lies to the south. On day 7 low pressure fills over the English
Channel, with NE'lies and northerlies for the UK.

Looking further afield
ECM shows low pressure over southern England on day 8 with NE'lies
elsewhere. The winds become northerlies on day 9 as the low moves over
France and on day 10 NW'lies cover the UK, as a ridge "topples" towards the
UK.
GFS brings easterlies on day 8 with a low to the SW. Day 9 sees the low move
over SW England, with southerlies for southern England and ENE'lies
elsewhere. Byda y 10 the low moves eastwards and NNE'lies cover the UK.

Ensemble analysis
(http://91.121.94.83/modeles/gens/gra...ille=Lond res)
The ensembles continue to show a gradual warming over the coming week, with
notably milder weather at the end of the year. Thereafter is a great deal of
scatter.