Here is a summary of the NWP output for 12z on Wednesday.
Issued 0555z, 20th January 2007.

The models show, in effect, the pattern resetting back to a zonal flow.
After the midweek northerly, it's likely the Azores High will settle over
mainland Europe, thus allowing mild SW'lies or WSW'lies to return over the
weekend. Beyond that the pattern is zonal, albeit with the jet so far north
southern areas of the UK will see less in the way of rain compared to
recently. MetO today is a wildcard though and instead shows what appears to
be retrogression and signs of a potent northerly. It has no support from any
other run, so is best regarded as a curiosity at this stage.

Analysis and evolution to T+120 via GFS
http://85.214.49.20/pics/Rtavn001.png
http://85.214.49.20/pics/avnpanel1.gif
Complex low pressure lies to the north and WNW, leading to strong to gale
force WSW'lies and SW'lies for the UK. The lows move eastwards tomorrow, as
the Azores High ridges towards Greenland. Strong westerlies and WSW'lies are
the result, with NNW'lies following behind a southwards moving trough. The
trough covers England and Wales for Monday, with NNW'lies elsewhere. By
Tuesday the Azores High sinks SE'wards towards the UK, bringing a mixture of
northerlies and NNW'lies.

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 strong northerly jet over the UK, with a marked
ridge to the west. At the 500hPa level there's an upper high to the west and
a trough extends across Scandinavia and central Europe. MetO has the same
overall pattern, but with a weaker trough to the east, while ECM is more
progressive and has the upper high closer to the UK. JMA is unavailable,
while NGP shows an elongated upper high "toppling" to the west of the UK.
Finally GEM has a colder pattern, with a deeper trough to the east and a
weaker high further to the west.
At the surface GFS shows the Azores High to the west and a ridge NE'wards
over Norway. Northerlies cover much of the UK, as is the case with MetO. ECM
brings NW'lies for all, with low pressure further away on the Continent. NGP
shows the Azores High toppling to the west, with a mixture of northerlies
for England and Wales and NW'lies elsewhere. GEM has a trough over the Low
Countries and strong NNW'lies across the UK.

Evolution to T+168
ECM shows a ridge from the Azores High covering the UK on day 6, leading to
northerlies and NW'lies. By day 7 the high sinks SE'wards, bringing SW'lies
to Northern Ireland and westerlies to Scotland, with NW'lies elsewhere.
GFS shows the Azores High moving slowly SSE'wards as a poweful jet roars
away to the NE and NW. On day 6 WNW'lies cover the UK with the high to the
WSW; by day 7 WNW'lies persist for most but for Northern Ireland and western
Scotland winds become SW'lies.

Looking further afield
Beyond T+168, ECM shows a strong zonal flow developing. Day 8 sees WSW'lies
and SW'lies, as the Azores High moves over France. Day 9 sees further
WSW'lies and day 10 sees yet more of the same, with pressure remaining high
to the south.
GFS also develops zonality, driven by a strong jet roaring away to the
north. WNW'lies affect all areas on day 8 as a weak ridge approaches from
the west, followed by WSW'lies on day 9. By day 10 another high merges with
the Azores High, leading to westerlies for all.

Ensemble analysis
(http://expert.weatheronline.co.uk/da...ia/ensdia.html - last
night's 18z)
The ensembles show the cold spell coming to an end by the end of the working
week, with temperatures aloft mostly above average by the weekend. Beyond
that the majority of the runs bring a "sine wave" zonal pattern, albeit all
out of phase with each other which leads to a mess on the charts!