Here is a summary of the NWP output for noon on Sunday.
Issued 0453, 18/01/12

The models are split again today, but in the opposite direction from a few
days ago. ECM paints a zonal picture, with low pressure persisting to the
north and winds from a westerly quarter from Sunday onwards. GFS, meanwhile,
shows the jet moving further south with much colder westerlies and,
eventually, northerlies for a time. The ECM ensembles are split into two
clusters, one showing relatively mild zonality and the other half showing
colder conditions, whereas the (18z) GFS ensembles are skewed more in favour
of milder zonality. As a result, the outlook is very uncertain today!

Analysis and evolution to T+120 via GFS
SSW'lies cover the UK, the result of a trough to the west. There are
WSW'lies tomorrow, with a deep low to the north. The winds become westerlies
on Friday, followed by further westerlies on Saturday. Pressure is low to
the north throughout.

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 strong and zonal flow over the Atlantic and the
UK. This leads to strong westerlies at the 500hPa level, while the other
runs have WNW'lies (MetO) or NW'lies (GEM, ECM, JMA).
At the surface GFS brings a weak ridge and WSW'lies. MetO also shows a ridge
and WSW'lies, while ECM has a ridge to the west with WNW'lies. GEM is
similar to ECM, as is JMA.

Evolution to day 7
ECM brings a ridge on day 6 with WNW'lies for most. On day 7 a trough
approaches from the west, leading to SW'lies.
SW'lies affect the UK on day 6 with GFS. A trough moves eastwards on day 7,
with SSW'lies in advance and with WNW'lies following behind.

Looking further afield
Days 8 to 10 with ECM show zonality, with SW'lies and WSW'lies across the
UK.
A trough covers the UK on day 8 with GFS, bringing westerlies and WNW'lies.
On day 9 there are NNW'lies as the trough moves eastwards. Day 10 sees a
ridge build across the UK, with cold northerlies for England and Wales and
milder southerlies for Northern Ireland and western Scotland.

Ensemble analysis
http://www.meteociel.com/cartes_obs/...&ville=Londres
The GEFS shows a zonal outlook.

ECM ensembles
http://www.meteogroup.co.uk/meteo/ep...tt6-london.gif
The ECM ensembles show two equally likely outcomes: a zonal outlook, or a
much colder outlook.