Here is a summary of the NWP output for 12z on Sunday.
Issued 0531z, 17th January 2007.

The models are still playing with the position and intensity of the high
that'll bring a cold spell to all. It's now looking more likely that the
high will "topple" over the UK in the latter half of the working week,
followed by a return to milder weather for all.

Analysis and evolution to T+120 via GFS
http://85.214.49.20/pics/Rtavn001.png
http://85.214.49.20/pics/avnpanel1.gif
Southerlies and SSW'lies cover the UK as the result of complex low pressure
to the NW. The low transfers eastwards tomorrow, bringing a period of strong
WSW'lies for much of the UK. By Friday the low moves over the Baltic,
leaving the UK under a weak ridge and westerlies. Saturday sees strong
SW'lies for all with complex low pressure to the NW.

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://85.214.49.20/pics/Rngp1201.gif
The jetstream chart shows a large ridge over the mid-Atlantic, with the jet
running northwards to the west of Greenland, over the plateau then
southwards to the west of the UK. The pattern's reflected at the 500hPa
level, with a large ridge heading northwards towards SE Greenland. MetO is
similar, albeit with the centre of gravity further northwards. ECM has less
of a ridge and JMA is very similar. GEM has a stronger ridge to the west and
NGP has much less of a ridge.
At the surface GFS shows a trough over SE England and a high to the SW of
Iceland. NW'lies cover much of the UK as a result. MetO shows a stronger
high to the west of the UK, this time with a trough over much of England.
England lies under NW'lies, with NNW'lies elsewhere. ECM shows NW'lies and
WNW'lies for the UK with a high to the WSW and a trough over northern
Scotland. JMA is again very similar to ECM. Westerlies cover the UK with
NOGAPS and GEM shows the trough clearing southern England, with NNW'lies
across the UK.

Evolution to T+168
ECM shows a double-centred Azores High to the west of the UK at T+144, as
heights rise strongly. Northerlies and NNW'lies are the result, followed by
NE'lies for most on day 7 as the high builds over Scotland and Northern
Ireland.
GFS brings a mixture of northerlies and NNW'lies over the UK on day 6 as the
high to the west builds. By day 7 it declines to the west, with further
northerlies for most.

Looking further afield
Beyond T+168, ECM shows a strong jet blasting away to the north. On day 8 a
ridge from the east covers Scotland and Northern Ireland, leading to strong
easterlies for England and Wales. Day 9 sees a ridge over Ireland, with
SW'lies for Scotland and Northern Ireland. Elsewhere, with a low over
France, winds are NNE'lies. By day 10 zonality returns with complex low
pressure to the NW and high pressure to the south and SW. Westerlies or
WSW'lies cover the UK as a result.
GFS shows the high swiftly "toppling" over the UK. On day 8 the UK lies
under westerlies and NW'lies as the high sinks southwards and by day 9 it
lies to the south, with SW'lies for all. Day 10 sees a trough move in from
the west with SW'lies in advance and westerlies following behind.

Ensemble analysis
(http://expert.weatheronline.co.uk/da...ia/ensdia.html - last
night's 18z)
The ensembles continue to show a cold spell on the way, albeit with slightly
higher temperatures on Sunday and with the return to -5C air for London a
day earlier, on the 25th rather than the 26th.