Here is a summary of the NWP output for noon on Monday.
Issued 0519, Christmas Eve 2009.

A battle will rage next week, with relatively cold air to the north and much
milder air to the south. GFS shows the mild air winning in the short term,
with rain spreading northwards to most areas on Monday into Tuesday. ECM is
less keen, however, maintaining the cold air over Scotland and Northern
Ireland early next week. Where the two air masses meet there's the potential
for some especially heavy rain (or even snow on the northern edge), however
at this stage the models are varying too much to give a definitive answer as
to where the battle lines will be drawn. By the end of the year it's likely
the colder air will win for a few days at least, with southern areas turning
colder again.

Analysis and evolution to T+120 via GFS
A slack low covers the UK, with light southerlies for many. Tomorrow the low
moves away to the east, leaving light northerlies over the UK. Boxing Day
sees SW'lies and southerlies, with milder air moving northwards. There are
further SW'lies for most on Sunday as the low moves over Scotland.

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 a strong and highly amplified jey over the North
Atlantic, with a secondary westerly jet to the north of the UK. A large
ridge has formed south of Greenland, with the majority of the energy going
into the northern branch of the jet. At the 500hPa level there's an upper
col, while ECM has upper westerlies with a low to the north. as does MetO.
GEM brings an upper low to the NNE with upper westerlies for the UK and JMA
has upper westerlies too.
At the surface, GFS brings strong easterlies with a low to the SW. ECM has a
col over England and Wales, with cold NW'lies elsewhere. MetO has a col over
Scotland and Northern Ireland, with SE'lies elsewhere. GEM shows a col for
Scotland and easterlies elsewhere, with a trough to the south, while JMA has
SE'lies and easterlies across the UK.

Evolution to T+168
ECM shows a weak ridge over Northern Ireland on day 6. Much of England and
Wales lie under ENE'lies, with NW'lies elsewhere. On day 6 the winds become
northerlies for most as low pressure moves southwards over the North Sea.
GFS brings low pressure over England on day 6, with strong northerlies
elsewhere. Strong NNW'lies cover the UK on day 7 as a high moves towards the
UK from the west.

Looking further afield
ECM shows a ridge over the UK on day 8, followed by strong westerlies on day
9 as high pressure to the west moves towards Greenland. On day 10 NW'lies
and westerlies cover the UK as low pressure deepens over Scandinavia.
GFS has northerlies on day 8 with a high to the west and a low over the
North Sea. Day 9 sees NE'lies as the high builds to the NW, followed by mild
NW'leis on day 10 as the high then drifts towards the UK.

Ensemble analysis
(http://91.121.94.83/modeles/gens/gra...ille=Lond res)
The ensembles show milder weather for the remainder of the year, with a
switch to colder conditions by the 1st.