Here is a summary of the NWP output for noon on Tuesday.
Issued 0520, 22nd January 2010.

The models except GFS show a colder interlude midweek, with some cold air
being advected westwards for a couple of days from mainland Europe. The cold
air is likely to stagnate for a day or two before westerlies or NW'lies
bring a return to milder air.

Analysis and evolution to T+120 via GFS
SSE'lies cover the UK, with a trough to the west. Tomorrow the trough fills
over SE England, with light winds for all. A col covers the UK on Sunday and
Monday.

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 strong jet to the north, with a weaker jet
heading SW'wards to the south of the UK. The British Isles lie under a
ridge. At the 500hPa level there's a high to the SW with SW'lies aloft. ECM
has a ridge over Scotland and Northern Ireland, with NE'lies aloft. MetO is
similar to ECM with upper NE'lies, as is the case with GEM. JMA has upper
NNW'lies with a similar pattern to the others (except GFS).
At the surface, GFS brings mild SW'lies across the UK with a high to the
south. ECM shows a ridge over the North Sea with southerlies for Scotland
and Northern Ireland and NE'lies elsewhere. MetO is very similar, while GEM
has ENE'lies for most with a large high to the NE. JMA also has ENE'lies for
most, with a small trough over SE England bringing NNE'lies there.

Evolution to T+168
ECM shows a col on day 6, followed by a ridge from the west on day 7. This
leads to NE'lies for much of England and Wales with westerlies elsewhere.
GFS brings WNW'lies and westerlies on days 6 and 7 respectively, as the
Azores High declines to the SW.

Looking further afield
ECM shows westerleis on day 8 with a high to the SW, followed by NW'lies on
day 9 as a trough moves SE'wards. Day 10 sees further NW'lies.
GFS has WNW'lies backing SW'ly on days 8 to 10, with high pressure to the SW
moving slowly eastwards.

Ensemble analysis
(http://91.121.94.83/modeles/gens/gra...ille=Lond res)
The GFS ensembles show a couple of cold days and then a return to average
conditions.

ECM ensembles
http://www.meteogroup.co.uk/meteo/ep...tt6-london.gif
ECM shows a cold snap midweek, followed by a return to near average
conditions.