Here is a summary of the NWP output for noon on Tuesday.
Issued 0522, 11th December 2009.

The latter half of the working week will see high pressure to the NW or WNW,
allowing a cold NE'ly flow to affect much of England and Wales, with the
potential for a wintry mixture of precipitation including snow. Scotland and
Northern Ireland are at less risk of snow, being closer to the high, but GFS
shows a chance there on Thursday.

Analysis and evolution to T+120 via GFS
High pressure covers the UK, with light winds for most. Tomorrow the high
builds to the northeast, introducing NE'lies to England and with SE'lies or
easterlies elsewhere. NE'lies move across England and Wales on Sunday as
high pressure crosses Scotland. By Monday the high declines over Scotland
and NE'lies persist 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 a ridge to the west and a strong westerly jet over
the Mediterranean. At the 500hPa level there's a cut-off high over Iceland
and a low over Biscay, with upper easterlies and NE'lies for the UK. ECM has
a high to the immediate NW of the UK, with upper northerlies as a result.
MetO, like GFS, has a high over Iceland and upper NE'lies for the UK. GEM
also has a high over Iceland, as does JMA.
At the surface, GFS brings NE'lies and northerlies with lows to the west and
SW. ECM brings much milder northerlies with high pressure to the west. MetO
shows cool NNE'lies due to a high over Iceland and GEM is much of the same.
JMA has a high over Iceland and a shallow low east of Scotland. Elsewhere
winds are ENE'lies.

Evolution to T+168
ECM shows NNE'lies on day 6 as the high moves westwards. On day 7 a ridge
moves southwards over the UK, with cold ENE'lies over much of England and
Wales and less cold NW'lies moving in elsewhere.
Strong and cold NE'lies cover the UK on day 6 with GFS, with a high to the
north and a low over Biscay. A ridge moves southwtards on day 7 with cold
NE'lies persisting for England and Wales. Elsewhere less cold NW'lies move
in.

Looking further afield
ECM shows NW'lies and WNW'lies on days 8 to 10 as high pressure sinks slowly
southwards to the west.
Days 8 to 10 with GFS show the blocking upper high moving over Iceland. Low
pressure lies to the NW on day 8, with SW'lies over much of the UK. The low
deepens on day 9, with the unusual situation of cold SSW'lies over the UK.
By day 10 the winds become ESE'lies and SE'lies as the low continues to
deepen to the NW. A second low to the south "props up" the block.

Christmas Day chart watch
http://www.wzkarten.de/pics/Rtavn3361.png
The chart for Christmas Day shows strong ESE'lies over the UK as low
approaches from the SW. Heavy rain in the far SW would turn readily to snow
as it moves northwards, bringing a white Christmas for many.

Ensemble analysis
(http://91.121.94.83/modeles/gens/gra...ille=Lond res)
The ensembles continue to show prolonged cold just around the corner.

Christmas countdown:
For midnight on Christmas Day, the ensembles show the following:
Southerlies / SE'lies: 6
Easterlies/NE'lies: 8
NW'lies: 1
High over UK: 1
Col: 1
Westerlies / SW'lies: 4

The ensembles still show an easterly flow of some sorts as the favoured
option, with even some of the SW'ly options still involving remnant cold air
over the UK.