Here is a summary of the NWP output for 12z on Saturday.
Issued 0542z, 12/12/06

There are signs of a change today. High pressure looks like increasinly
influencing the UK from the south. Northern and western areas are at a
greater risk of seeing rain, but it's now looking quite dry for southern and
eastern areas. There's also the chance of an inversion setting up in the
latter areas, rendering the 850hPa charts somewhat academic.

Analysis and evolution to T+120 via GFS
http://85.214.49.20/pics/Rtavn001.png
http://85.214.49.20/pics/avnpanel1.gif
SW'lies cover the UK with a deep low to the north. A weak ridge brings
WSW'lies tomorrow, followed by SW'lies on Thursday as a new low moves
NE'wards to the NNW of the UK. The SW'lies persist on Friday.

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.jpg /
http://85.214.49.20/pics/Rukm1201.jpg
http://85.214.49.20/pics/Recm1201.jpg /
http://85.214.49.20/pics/Rngp1201.jpg
The jetstream chart shows a weaker jet than recently over the North Atlantic
with a marked shortwave pattern. An upper ridge covers the UK with a weak
trough to the east. MetO shows a flat gradient and ECM has a weak trough
over the British Isles instead. JMA and NGP show a flat gradient over the UK
with a trough to the north, while GEM shows lower heights and more of a
trough to the north.
At the surface GFS shows a ridge from a high over Biscay. Winds are
westerlies and WSW'lies, whereas with MetO they're WSW'ly for all, also due
to a high to the south. ECM brings westerlies for all instead, with a weak
trough to the east and a high to the WSW. NGP brings WSW'lies for the UK, as
does JMA. GEM is the odd run out, with a low to the NE, a trough over the UK
and a mixture of westerlies and WNW'lies as a result.

Evolution to T+168
ECM shows an upper ridge building to the west. On day 6 a surface high
builds to the WSW, leading to NW'lies over the UK. On day 7 the high builds
and drifts eastwards, allowing WSW'lies to affect the UK.
GFS brings WSW'lies over the UK on day 6 as heights rise to the west. The
upper ridge moves over the UK on day 7, associated with a surface ridge over
England and Wales. Elsewhere winds are westerlies or WSW'lies.

Looking further afield
ECM shows a ridge over the UK on day 8 with light westerlies, followed by
SW'lies on day 9 as the ridge moves eastwards. By day 10 another ridge
builds over the UK with a mixture of northerlies and westerlies for the
British Isles.
SW'lies cover the UK on day 8 with a low to the north and a ridge to the
west. The ridge builds strongly NE'wards on day 9, leaving the UK under
light winds. By day 10 high pressure covers the North Sea, drawing a
southerly flow over Scotland and Northern Ireland, with SE'lies elsewhere.

Ensemble analysis
(http://expert.weatheronline.co.uk/da...ia/ensdia.html - last
night's 18z)
The "sine wave" effect of the past few weeks is still present, but in a more
exaggerated form. Over the next few days 850hPa temperatures will reach a
peak (around +9C in London) before falling away to be below average during
Sunday. A gradual rise follows during the following week.