Here is a summary of the NWP output for noon on Tuesday.
Issued 0439, 08/03/13

The middle of the week looks to be cold for most, with widespread frosts by
night. Winds will be from a northerly quarter and there'll be an ongoing
risk of showers, especially in the east, with showers likely to be of sleet,
soft hail or snow.

Analysis and evolution to T+120 via GFS
Easterlies cover the UK with a trough to the south. Tomorrow there's a col
over England and Wales with easterlies and ESE'lies elsewhere, followed by
ENE'lies on Sunday. Monday sees strong ENE'lies and NE'lies over the UK.

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 northerly flow with a ridge to the west and
a trough to the NE. At the 500hPa level there's also a northerly flow,
something which is a common feature of all the models today.
At the surface the models all show northerlies or NNW'lies with a high to
the west.

Evolution to T+168
ECM shows NW'lies on day 6 and a col on day 7. GFS has light NW'lies on day
6 too, also followed by a col on day 7.

Looking further afield
ECM shows SE'lies on days 8 and 9 as low pressure moves slowly NE'wards to
the west. On day 10 a col covers the UK. GFS has a low over Scotland on day
8 with a col elsewhere, followed by light SE'lies for most on day 9 as the
low moves SW'wards and fills. Day 10 brings southerlies with low pressure to
the west.

Ensemble analysis
http://www.meteociel.com/cartes_obs/...&ville=Londres
The GEFS delays the onset of cold by one day, with an exceptionally cold
Monday followed by rather cold conditions for at least a week.

ECM ensembles
http://www.weathercast.co.uk/service...-forecast.html
ECM still shows cold weather arriving on Monday, with mean maxima below 5C
for 5 days afterwards.