Here is a summary of the NWP output for noon on Sunday.
Issued 0527, 9th December 2009.

Next week will start with high pressure to the WNW or NW and northerlies or
NNE'lies over the UK. These won't be especially cold for most (although
there's a risk of some cold air for the far SE). During the first half of
the week the high will move towards Iceland and there's a growing risk of a
significant and snowy cold spell as a result.

Analysis and evolution to T+120 via GFS
A deep low lies to the WNW, with strong southerlies and SSW'lies over the
UK. Tomorrow pressure builds to the south, with lighter WSW'lies as a
result. Friday sees high pressure over much of the UK, with southerlies and
SE'lies as a result. By Saturday the high builds to the NE, introducing
NE'lies for England and easterlies or SE'lies elsewhere.

T+120 synopsis
http://91.121.93.17/pics/Rtavn12015.png /
http://91.121.93.17/pics/Rtavn1201.png
http://91.121.93.17/pics/Rukm1201.gif
http://91.121.93.17/pics/Recm1201.gif /
http://www.meteociel.fr/modeles/nogapse_cartes.php
The jetstream chart shows an omega block centred over Iceland. The majoriy
of the jet's energy is in the southern branch, which runs eastwards to the
south of the Azores. At the 500hPa level there's a cut-off high over Iceland
and upper NNE'lies for the UK. ECM shows an upper high over Scotland and
Northern Ireland, while MetO has an upper high to the west and northerlies
aloft. GEM brings an upper high over Scotland and Northern Ireland as per
ECM, while JMA has a high to the NW.
At the surface, GFS brings northerlies with a high to the NW and a low over
the Netherlands. ECM has a high centred over the UK, while MetO has a high
over the Western Isles with northerlies for rest of the UK. GEM shows a high
over the UK and JMA also has a high over the UK.

Evolution to T+168
ECM shows the upper high retrogressing NW'wards on day 6, with NW'lies over
the UK as a result. NNE'lies affect the UK on day 7 as the surface high also
moves NW'wards over Iceland.
Cold NE'lies cover the UK with GFS on day 6, with high pressure over
Greenland. An upper trough extends across the UK from the east on day 7,
with cold ENE'lies for all.

Looking further afield
ECM shows a ridge over the UK on day 8 with NE'lies, northerlies and
NW'lies. On day 9 low pressure deepens to the north, bringing westerlies.
The low deepens over the North Sea on day 10, bringing WSW'lies to southern
England and cold ENE'lies elsewhere.
Day 8 with GFS shows high pressure over Greenland and very cold, snowy
NE'lies for the UK. A low deepens over Norway on day 9, leaving the UK under
a col with a severe frost. Day 10 sees WSW'lies over the UK as the
Scandinavian low deepens.

Ensemble analysis
(http://91.121.94.83/modeles/gens/gra...ille=Lond res)
The ensembles show a cold spell on the way.

*NEW* - Christmas Countdown!
For midnight on Christmas Day, the ensembles show the following:
Southerlies / SE'lies: 4
Col: 2
Low over the UK: 2
Easterlies: 7
NW'lies: 1
Westerlies / SW'lies: 5

Easterlies take an early lead, although only 3 of the 21 runs have -5C or
lower 850s for London. The most notable difference this year is the great
reduction in members which show SW'lies; normally at this range it's the
most common option.