Here is a summary of the NWP output for noon on Tuesday.
Issued 0441, 18/01/13

The middle of next week will see cold conditions across the UK with ECM and
MetO both showing trough disruption bringing widespread precipitation; over
northern areas it's likely to be snow but further south a mixture of rain
and sleet is more likely. GFS, meanwhile, is off on its own with strong
westerlies for all by day 6.

Analysis and evolution to T+120 via GFS
SE'lies cover the UK ahead of a trough to the west. Tomorrow there are
ESE'lies as the trough disrupts, followed by ENE'lies on Sunday from a weak
high to the NE. Monday sees low pressure over southern areas, with less-cold
air entrained. Further north there are ESE'lies.

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 zonal jet over the western and central
Atlantic, splitting in two as it reaches the UK. At the 500hPa level there's
a col, whereas MetO has an upper low to the SW. ECM shows an upper low over
the Irish Sea, while GEM has an upper low to the SW as with the MetO run.
JMA has an upper trough extending across the UK from the west.
At the surface GFS brings a col. MetO has ENE'lies with a low to the south,
while ECM has a low to the west and SSE'lies over the UK. GEM brings
SE'lies and ESE'lies, while JMA has a mixture of southerlies and SE'lies.

Evolution to T+168
ECM shows SE'lies over the UK on days 6 and 7 as a trough disrupts to the
south and SW. GFS brings a trough eastwards on day 6 with WSW'lies for all,
followed by a weak ridge and light winds on day 7.

Looking further afield
Days 8 to 10 with ECM bring a col followed by southerlies as pressure builds
to the east and SE. GFS brings SW'lies and westerlies on days 8 to 10 with
low pressure near Iceland and troughs crossing the UK from the west.

Ensemble analysis
http://www.meteociel.com/cartes_obs/...&ville=Londres
The GEFS shows cold or very cold conditions for the next week, followed by a
return to nearer-normal conditions.

ECM ensembles
http://www.weathercast.co.uk/service...-forecast.html
ECM now shows less-cold conditions from the 24th (rather than the 26th).