Here is a summary of the NWP output for noon on Wednesday.
Issued 0520, 8th December 2007

The change is still on the way. Initially mild southerlies on Wednesday are
likely to back SE'ly for most by Friday, drawing colder Continental air over
the UK. Although temperatures aloft are relatively mild, it's llikely
there'll be some frosts inland over southern and eastern England, with frost
lingering in the shade by day where winds are light. Elsewhere it'll be less
cold and for western Scotland and Northern Ireland, windy and milder still.
This is the scenario offered by ECM and GFS, anyway, as MetO isn't keen on
centreing the high to the NE.

Analysis and evolution to T+120 via GFS
http://85.214.49.20/pics/Rtavn001.png
A weak ridge covers the UK, with gusty westerlies as a result. Complex low
pressure moves over the UK tomorrow, bringing strong to gale force SW'lies
to much of the UK. By Monday the low fills over the Netherlands, with
NW'lies for the UK. A ridge builds over Northern Ireland and Scotland on
Tuesday, with NW'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.gif /
http://85.214.49.20/pics/Rukm1201.gif
http://85.214.49.20/pics/Recm1201.gif /
http://www.meteociel.fr/modeles/nogapse_cartes.php
The jetstream chart shows a meridonal pattern over the Atlantic, with a very
strong jet heading northwards over Iceland. The UK lies under a large ridge
and the same is true at the 500hPa level, with a ridge extending across the
UK and into Scandinavia. MetO has a ridge over the UK too, with a secondary
ridge NE'wards over Scandinavia. ECM has a ridge over the UK too, with an
extension to Scandinavia. NGP is similar to ECM and GEM also shows a ridge
over the UK.
At the surface GFS brings SSE'lies, with high pressure over southern
Scandinavia and a ridge over the North Sea. The winds are light in the east
of the UK but become increasingly strong the further west you are. MetO has
southerlies and SSW'lies, with high pressure over southern Germany and
northern France, while ECM has a high over southern Scandinavia and a ridge
SSW'wards to France. Southerlies are the result for the UK. NGP brings a
ridge over England and Wales, with SSW'lies elsewhere, while GEM shows
southerlies for all and two highs; one to the NE and one to the SE.

Evolution to T+168
ECM shows an upper high building strongly over the North Sea. The surface
high is centred over the Skaerrak, with SSE'lies and southerlies for the UK
on day 6. By day 7 the high declines over the North Sea, leading to
easterlies for England and Wales, with SE'lies elsewhere.
On day 6 the GFS brings high pressure over southern Sweden. This leads to a
mixture of NE'lies and ENE'lies for England and Wales, with SE'lies or
SSE'lies elsewhere. On day 7 the high declines and drifts southwards,
bringing easterlies across England and Wales, with SE'lies for Scotland and
Northern Ireland.

Looking further afield
Days 8 to 10 with ECM see the high slowly decline over the North Sea. Winds
are a mixture of easterlies (for England and Wales) and SE'lies (elsewhere)
throughout, lightest over eastern parts of England.
The GFS shows the high declining on day 8, still with easterlies and SE'lies
over the UK. The winds become easterlies and southerlies on day 9 as the
high sinks SE'wards, over western Germany. By day 10 SE'lies and southerlies
cover the UK, with high pressure persisting to the east.

Ensemble analysis
(http://expert.weatheronline.co.uk/da...ia/ensdia.html - last
night's 18z)
The ensembles for London show a marked rise in pressure from the 11th
onwards, with a warm spell on the 12th and 13th as southerlies are drawn
across the UK. Beyond that there's a marked cooling trend. The cooling is
reflected in the ECM ensembles for De Bilt, with mean temperatures hovering
below freezing over there by the 16th.