Here is a summary of the NWP output for noon on Friday.
Issued 0452, 30/01/12

The working week is going to be a cold or very cold one for most, with
widespread frosts and the risk of snow showers on many eastern coastal
areas. The end of the week is less certain and the models are all going
their own ways.

GFS shows a small low moving in from the east, which then gets deflected
southwards and prolongs the cold block - a very cold weekend to come. ECM
has milder weather pushing in from the west with transitory snow over the
weekend, followed by a renewed cold push next week. MetO is the keenest to
break down the cold spell, with milder southerlies pushing across the UK
during the weekend and no disrupting low as per the ECM.

Much hinges on developments to the east (in particular, whether the low
forms as GFS shows) and the path of the jetstream to the west is also vital
in terms of either prolonging or collapsing the block; a bifurcated jet
causing trough disruption (as in ECM) would prolong the spell, whereas a
lack of trough disruption would being an abrupt end (as per MetO).

Analysis and evolution to T+120 via GFS
A ridge from the NE covers the UK. There are easterlies and ESE'lies across
much of England and Wales with SE'lies elsewhere. Tomorrow there are further
easterlies and ESE'lies over the UK with a trough disrupting to the west.
Pressure builds to the NE on Wednesday, delivering very cold ENE'lies across
England and Wales, with ESE'lies or easterlies elsewhere. Pressure continues
to build on Thursday, with bitterly cold NE'lies over much of England and
Wales and cold SE'lies elsewhere.

T+120 synopsis
http://www.wetterzentrale.de/wz/pics/Rtavn12014.png
http://www.wetterzentrale.de/wz/pics/Rtavn1201.png
http://www.wetterzentrale.de/wz/pics/Rukm1201.gif
http://www.wetterzentrale.de/wz/pics/Recm1201.gif
http://www.wetterzentrale.de/wz/pics/Rjma1201.gif
The jetstream chart shows a weak ridge over the UK with a marked shortwave
pattern heading NE'wards across the Atlantic. At the 500hPa level there's a
cyclonic northerly flow, with a ridge extending NNE'wards to the west. An
upper cold pool lies over Germany. MetO and JMA are more progressive and
both have a ridge over the UK. ECM is closer to GFS, with upper northerlies,
while GEM has a col aloft.
At the surface GFS shows a ridge from the NE over the UK, with a nearby low
over northern France. Cold and unstable NNE'lies cover much of England and
Wales, with southerlies elsewhere. MetO has southerlies across the UK with a
high over Belgium, while ECM has everything further west with a high over
the Welsh border - winds are light for most as a result. GEM brings SSE'lies
for England and Wales with a ridge over the SE; Scotland lies under
WSW'lies. JMA has southerlies for all with a ridge to the SE.

Evolution to day 7
ECM brings SSW'lies across the UK on day 6 with milder air pushing
eastwards. On day 7 a trough crosses the UK, resulting in NW'lies in its
wake.
GFS has a ridge over much of England and Wales on day 6 with cold air
entrenched. Further north and west there are southerlies but at this stage
they're far from mild. On day 7 pressure builds again over northern England,
bringing NNE'lies further south and with southerlies persisting for Scotland
and Northern Ireland.

Looking further afield
Days 8 to 10 with ECM show high pressure rebuilding from the east. Day 8
sees light winds and a ridge, followed by SE'lies and SSE'lies for most on
day 9. By day 10 the ridge moves northwards, allowing cold ENE'lies to cover
the UK.
GFS shows high pressure building over the UK on days 8 to 10 with generally
light winds as a result.

Ensemble analysis
http://www.meteociel.com/cartes_obs/...&ville=Londres
The GEFS shows a cold week ahead, followed by a great deal of uncertainty
from Saturday onwards.

ECM ensembles
http://www.meteogroup.co.uk/meteo/ep...tt6-london.gif
ECM also shows a cold week to come, followed by a probable warming over the
weekend.