Here is a summary of the NWP output for noon on Tuesday.
Issued 0518, 25th Jan 2008

There are signs of a change today. The latter half of the working week will
see a large upper ridge heading towards Greenland, which will have the
effect of displacing an upper low SE'wards towards the UK. Some cold air
will be drawn across the UK as a result, although the models differ greatly
regarding the extent and depth of the cold pool. At the moment it's likely
that all areas will see rain on Thursday and/or Friday, with snow likely for
much of Scotland.

GFS takes this a stage further, showing heavy snow and gales (ie "proper"
blizzards) across a great swathe of northern Britain next Friday, which
would cause widespread disruption were it to verify. There's only limited
support for the scenario in the 0z ensembles, however, with most showing
lighter winds and/or rain instead. 15 of 21 ensemble members show snow
across Scotland by T+168, however.

Longer term, there are two options on offer. Either the high to the west
"topples" and we return to the mild weather we're currently having, or the
ridge near Greenland splits later this week, allowing a repeat performance
in around 10 days time (as shown by the operational GFS today).

Analysis and evolution to T+120 via GFS
http://85.214.49.20/pics/Rtavn001.png
High pressure lies to the south, leading to SW'lies for all. There's little
change tomorrow, with further SW'lies. The winds become WSW'lies on Sunday
as pressure remains high to the SE. On Monday lighter SW'lies cover the UK,
with high pressure persisting to the south.

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/Rukm1201.gif
http://85.214.49.20/pics/Recm1201.gif /
http://www.meteociel.fr/modeles/nogapse_cartes.php
The jetstream chart shows a strong jet over the North Atlantic, with a
marked trough to the west of the UK. At the 500hPa level there's also a
large trough to the west, with a ridge to the east and upper SW'lies for the
UK. ECM and GEM both show a shallower trough to the west, with upper SW'lies
for the UK. MetO has a deeper trough, as per GFS.
At the surface GFS brings a low over the Celtic Sea, with southerlies for
England and Wales. Northern Ireland lies under NE'lies and Scotland lies
under light winds. ECM has westerlies and WSW'lies for the UK, with a
shallow trough over Ireland. GEM is similar, with westerlies and WSW'lies
too. MetO has a deeper trough to the west and a mixture of SW'lies and
SSW'lies for the UK as a result.

Evolution to T+168
ECM shows a trough to the west and WSW'lies for the UK on day 6. On day 7
the trough moves over the UK, bringing further WSW'lies.
Complex low pressure lies to the NW and NE with GFS on day 6. Cool WSW'lies
cover the UK as a result, followed by strong to gale force NW'lies, WNW'lies
and westerlies as low pressure deepens explosively over the North Sea on day
7. GFS progs widespread minima below freezing, meaning widespread blizzards
would result.

Looking further afield
By day 8 ECM shows WNW'lies, as a weak ridge moves in from the west. Some
notably cold air briefly affects Scotland. By day 9 the winds become
WSW'lies, as a low forms to the ENE and the cold air moves eastwards. Day 10
sees SW'lies for all, with deep low pressure near Iceland.
A weak ridge covers the UK on day 8 with GFS, leading to a mixture of
westerlies and WSW'lies. On day 9 another low deepens to the NE, bringing
SW'ly gales and torrential rain. The rain turns to snow for the northern
half of the country on day 10 as the low moves NE'wards and fills, dragging
in cold SW'lies and NW'lies in its wake.

Ensemble analysis
(http://91.121.94.83/modeles/gens/gra...ille=Lon dres)
The ensembles continue to show mild weather for the next 5 or 6 days,
followed by colder and wetter conditions.