Here is a summary of the NWP output for noon on Thursday.
Issued 0525, 16th March 2008

A change is on the way. During Thursday a trough will move southwards
in association with a deep low to the NE. The low will move slowly
ESE'wards and as the trough clears the UK during Friday much colder
conditions will develop, with widespread precipitation. Over northern
hills this is likely to be in the form of snow, whereas elsewhere a
wintry mixture of rain, hail, sleet and the odd snow flurry. Northern
areas are at the greatest risk of seeing snow, but it cannot be ruled
out over most of the UK. During the weekend the winds will ease
somewhat and the rain/sleet/hail/snow will become more showery in
nature. Temperatures are still likely to be on the low side overall.

Analysis and evolution to T+120 via GFS
http://85.214.49.20/pics/Rtavn001.png
Low pressure covers southern England, leading to NE'lies for most.
Tomorrow a ridge builds from the NW, leading to northerlies and
NNW'lies. Tuesday sees the winds become NNW'lies as high pressure
persists to the NW. On Wednesday the high builds and sinks SE'wards,
bringing NW'lies and NNW'lies.

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 complicated flow over the North Atlantic,
with a large blocking ridge supported by a weak southerly jet. The
northern branch is much stronger and passes from NW to SE over the UK.
At the 500hPa level there's an upper low to the north and a large
upper high north of the Azores, with an upper low over the Azores
supporting the high. MetO has an upper ridge over the UK, with upper
NW'lies, while ECM has stronger upper NW'lies with a tighter gradient
aloft. GEM brings upper WNW'lies with an upper low north of the UK.
At the surface GFS brings strong to gale force WNW'lies, with a
trough to the east and high pressure to the west. MetO has lighter
westerlies with low pressure to the north, while ECM has low pressure
to the NNE and strong westerlies for the UK as a result. Strong
westerlies also feature with GEM, which has a low to the immediate
north of the UK.

Evolution to T+168
ECM brings strong NNW'lies on day 6, with low pressure over southern
Sweden. The winds ease as the low fills on day 7.
A deep low lies to the east on day 6 with GFS, bringing strong to gale
force NW'lies and NNW'lies. A secondary low moves SE'wards on day 7,
bringing NW'lies and westerlies over the UK.

Looking further afield
ECM brings light to moderate northerlies on day 8, with complex low
pressure to the east and a weak ridge to the west. NW'lies cover the
UK on day 9 as a secondary low heads southwards to the west, followed
by stronger NNW'lies on day 10 as the secondary moves SE'wards and
deepens over France.
Day 8 with GFS shows NW'lies with low pressure over the North Sea. Day
9 sees NNW'lies as a ridge moves towards the UK from the NW and by day
10 the ridge moves SE'wards, bringing NW'lies and WNW'lies to the UK.

Ensemble analysis (http://91.121.94.83/modeles/gens/graphe_ens3.php?
x=306&ext=1&y=141&run=18&ville=Londres)
The ensembles show a cool few days ahead, followed by a milder "blip"
on Thursday into Friday. Thereafter a prolonged cool spell looks
likely.