Here is a summary of the NWP output for 12z on Tuesday.
Issued 0557z, 12th January 2007.

The outlook remains unsettled and windy for the UK, but with a chance of
some colder conditions for a day or two in 10 days time. As ever, more runs
are needed.

Analysis and evolution to T+120 via GFS
http://85.214.49.20/pics/Rtavn001.png
http://85.214.49.20/pics/avnpanel1.gif
A weak ridge covers the UK, bringing moderate WSW'lies and SW'lies across
the UK. The ridge moves eastwards tomorrow, allowing further SW'lies and
WSW'lies to affect the UK. By Sunday a low deepens over Denmark, bringing
westerlies to the UK. Monday sees a high build to the ESE, leading to
SW'lies for all.

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/Rjma1201.gif /
http://85.214.49.20/pics/Rukm1201.gif
http://85.214.49.20/pics/Recm1201.gif /
http://85.214.49.20/pics/Rngp1201.gif
The jetstream chart shows a a strong zonal flow across the Atlantic from the
Eastern Seaboard to Scandinavia and beyond, via Scotland and Northern
Ireland. At the 500hPa level heights are high over much of central and
southern Europe, with a deep upper low to the south of Greenland. A SW'ly
gradient covers the UK, MetO and ECM also show a SW'ly gradient, the latter
with lower heights over the UK. JMA is very similar to ECM and the other
minor runs, GEM and NGP, show a SW'ly gradient as well.
At the surface GFS brings SW'lies for all with low pressure to the NW, while
MetO brings westerlies and WSW'lies as a trough moves swiftly across the UK.
ECM has a weak ridge over England and Wales with WSW'lies elsewhere. JMA is
similar to ECM while NGP also has a trough across the UK, as with MetO. GEM
shows a ridge affecting the UK, leading to SW'lies and WSW'lies.

Evolution to T+168
ECM shows strong SW'lies moving across the UK on day 6 as a secondary low
moves closer to Ireland. By day 7 the low moves NE'wards, allowing WSW'ly
gales to affect the UK.
GFS brings SW'lies and WSW'lies over the UK on day 6 due to complex low
pressure to the north and west. On day 7 the lows merge over the Northern
Isles, bringing westerly gales elsewhere.

Looking further afield
Beyond T+168, ECM shows westerlies for days 8 and 9, as a ridge moves
swiftly eastwards across the North Atlantic, declining as it does so. By day
10 the remnants of the ridge lie to the east, with strong SSW'lies ahead of
the next low affecting the UK.
GFS shows a deep low west of Ireland on day 8, resulting in strong SE'lies
for Scotland and Northern Ireland and SW'lies elsewhere. By day 9 the low
moves away to the NW, allowing lighter, colder WNW'lies and westerlies to
affect the UK. On day 10 a weak ridge lies to the west with a col and light
winds for much of the UK.

Ensemble analysis
(http://expert.weatheronline.co.uk/da...ia/ensdia.html - last
night's 18z)
The ensembles continue to show a "sine wave", mobile setup for the next 8 or
9 days. Beyond that there's unusually good agreement of a colder interlude,
with the potential for the -5 850 isotherm to reach London for the first
time this winter. The colder interlude also appears on ensemble charts
elsewhere in the UK.