Here is a summary of the NWP output for 12z on Christmas Day.
Issued 0539z, 21/12/06

High pressure will affect much of the UK until Boxing Day, but thereafter it
looks like the high will drift eastwards, allowing much milder southerlies
to affect the UK once the cold surface air moves away.

Analysis and evolution to T+120 via GFS
http://85.214.49.20/pics/Rtavn001.png
http://85.214.49.20/pics/avnpanel1.gif
High pressure is centred over the SW of the UK, with light winds for most
areas. The high builds tomorrow, with light winds persisting for England and
Wales. Elsewhere winds are WSW'lies, followed by SW'lies and SSW'lies for
Scotland and Northern Ireland on Saturday as the high moves eastwards. By
Christmas Eve the high is centred over the North Sea, with light easterlies
for England and Wales and southerlies or SSW'lies elsewhere.

T+120 synopsis
http://85.214.49.20/pics/Rtavn12015.png /
http://85.214.49.20/pics/Rtavn1201.png
http://85.214.49.20/pics/Rjma1201.jpg /
http://85.214.49.20/pics/Rukm1201.jpg
http://85.214.49.20/pics/Recm1201.jpg /
http://85.214.49.20/pics/Rngp1201.jpg
The jetstream chart shows a marked ridge over western Europe, with a ridge
over the UK. At the 500hPa level there's a high to the east, as is the case
with MetO (which shows a stronger high). ECM has a stronger high still, this
time over England and Wales. Of the minor runs, NGP is similar to ECM with
the upper high over England and Wales, as is the case with JMA. GEM has the
high further east, over Belgium.
At the surface GFS brings southerlies across the UK with high pressure atop
Germany. MetO also has a high to the east but this time it brings light
SE'lies for most areas. ECM has a ridge over England and Wales with SW'lies
and WSW'lies elsewhere, as is the case with NGP and JMA. GEM shows the high
over Germany and a mixture of southerlies and SSW'lies for the UK.

Evolution to T+168
ECM shows a zonal flow to the north of the UK and the high slowly declines
and moves southwards. On day 6 much of England and Wales lie under light
winds with westerlies for Scotland and SW'lies for Northern Ireland. By day
7 SW'lies cover the whole of the UK, albeit quite light over southern
England.
GFS brings southerlies across the UK on days 6 and 7 with low pressure to
the west and a ridge to the east.

Looking further afield
Beyond T+168, ECM shows strengthening WSW'lies across the UK as a deep low
moves ENE'wards over Iceland.
GFS shows strong southerlies on day 8 with a low to the SW. The low fills to
the west of Scotland on day 9, bringing southerlies to Scotland, SW'lies to
much of England and Wales and westerlies for Northern Ireland. Southerlies
return on day 10 as a new low lies to the west.

Ensemble analysis
(http://expert.weatheronline.co.uk/da...ia/ensdia.html - last
night's 18z)
The ensembles show above average 850hPa temperatures for at least another 7
to 10 days.