Here is a summary of the NWP output for 12z on Wednesday.
Issued 0554z, 16/12/06

It still looks as though a spell of settled weather is on the way for all
areas. Temperatures should fall to average or below average across most
areas, although places with an onshore breeze will probably stay a fair bit
milder. Longer term the models agree on a return to westerlies or SW'lies by
Christmas, but that's still a fair way off yet. As ever, more runs are
needed.

Analysis and evolution to T+120 via GFS
http://85.214.49.20/pics/Rtavn001.png
http://85.214.49.20/pics/avnpanel1.gif
A trough covers the far SE of the UK, with light winds elsewhere as a ridge
moves in from the west. WSW'lies cover the UK tomorrow as a low moves
ESE'wards and fills to the north. By Monday a weak ridge covers England and
Wales, with SW'lies, while a trough over Ireland brings SSE'lies elsewhere.
On Tuesday pressure builds strongly over England, Ireland and Wales with
westerlies for Scotland and Northern Ireland.

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 strong jet across the North Atlantic, heading
northwards over Iceland and up over Svalbard. It then loops back on itself
and heads south over Russia then SW'wards across the Baltic, Germany and
France. The UK lies under an upper ridge and this is reflected on the 500hPa
charts, with the centre to the NE of Scotland. MetO has a stronger upper
high centred over the UK, as is the case with ECM. JMA centres the high over
Scotland, as do NGP and GEM.
At the surface GFS shows a large high over the Baltic and a ridge westwards
across the UK. Winds are SSW'lies for Northern Ireland and Scotland, with
light easterlies over England and Wales. MetO shows a high over England and
Wales with SW'lies elsewhere, as is the case with ECM. JMA has the high over
Germany with light winds for the UK and NGP centres the high over the Celtic
Sea, leading to WNW'lies and westerlies for the UK. GEM shows the high over
northern England, with SW'lies for Scotland and Northern Ireland; elsewhere
winds are much lighter.

Evolution to T+168
ECM shows the high building and moving SW'wards. On day 6 SW'lies cover much
of the UK as the high builds over southern England, followed by westerlies
for all on day 7 as the high moves towards the Azores.
GFS, as yesterday, shows something quite different. The high over the Baltic
builds on day 6, with England and Wales under a ridge. Elsewhere winds are
moderate SW'lies, with a deep low near Iceland. By T+168 mild SW'lies affect
the UK as the Baltic High moves southwards over Germany.

Looking further afield
ECM shows westerlies for all on days 8 to 10 as low pressure moves eastwards
to the north and the Azores High retrogresses slowly.
GFS brings SW'lies across the UK on days 8 and 9, with high pressure from
the Azores to the Alps and beyond. By Boxing Day pressure builds over the
south of the UK with westerlies for Scotland and Northern Ireland.

Ensemble analysis
(http://expert.weatheronline.co.uk/da...ia/ensdia.html - last
night's 18z)
The ensembles continue to show good agreement of a cold few days, followed
by much milder air aloft moving in. The ensembles paint a largely dry
picture until the 23rd (Scotland) or Christmas Day (southern England).