Here is a summary of the NWP output for 12z on Boxing Day.
Issued 0539z, 22/12/06

High pressure will affect much of the UK for the next 4 or 5 days at least,
before slowly moving away eastwards and leaving southerlies in its wake.
Although the GFS is very keen on moving the high rapidly eastwards (as it
has been for the past few runs) it receives very little support from the
other models, again as with the past few runs. Confidence is thus high for a
change to milder weather for many areas (except Scotland, which is already
largely mild) next week, but low with regards to timing.

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 covers England and Wales, with westerlies or SW'lies
elsewhere. There's little change tomorrow, but on Christmas Eve the high
moves eastwards. By then easterlies cover England and Wales with southerlies
and SSW'lies elsewhere. Christmas Day sees SE'lies and southerlies over the
UK with high pressure over the North Sea.

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 ridge over the UK and much of Europe. At the
500hPa level there's a ridge to the east and a trough to the west, with an
upper souutherly flow over the British Isles. MetO shows a stronger high
over the North Sea, as does ECM. Of the minor runs, JMA is similar to MetO
and ECM, GEM has a high to the SE and NGP has the upper high over the UK
instead.
At the surface GFS shows southerlies with a low to the west and high
pressure over eastern Europe. MetO has the high much closer to the UK, over
the North Sea, leading to easterlies for SE England, SE'lies for the rest of
England and Wales, SSE'lies for Northern Ireland and SSW'lies for Scotland.
ECM has the high centred over East Anglia with similar winds to the MetO.
JMA brings SE'lies across most of the UK with high pressure over the North
Sea, while NGP has high pressure atop the UK with westerlies for Scotland
and light winds elsewhere. GEM is more progressive with high pressure over
France and SW'lies across the UK.

Evolution to T+168
ECM shows the upper high moving SW'wards. On day 6 southerlies cover
Scotland and Northern Ireland with a ridge and light winds elsewhere. By day
7 the surface high lies over France with SW'lies for all.
GFS brings increasingly strong southerlies over the UK as the high moves
away SE'wards, over Turkey. Complex low pressure lies to the west
throughout.

Looking further afield
Beyond T+168, ECM keeps high pressure to the east or SE. SW'lies cover the
UK on day 8, followed by SSW'lies on day 9 as a trough approaches from the
west. The trough fills over Scotland on day 10, with further southerlies and
SSW'lies for the UK.
GFS shows an increasingly unsettled outlook beyond day 7. On day 8 a trough
crosses the UK with southerlies in advance and SW'lies following behind.
SW'lies affect all areas on day 9, followed by strong to gale force SW'lies
and WSW'lies on day 10 from a deep low east of Scotland.

Ensemble analysis
(http://expert.weatheronline.co.uk/da...ia/ensdia.html - last
night's 18z)
The ensembles show good agreement of 850hPa temperatures slowly falling over
the next week, followed by a "sine wave" effect from a more mobile setup.