Here is a summary of the NWP output for 12z on Thursday.
Issued 0541z, 14th January 2007.

There's a change on the way, with mild and wet weather giving way to a brief
colder interlude; there might even be a frost or two! There's considerable
disagreement between the models regarding the fate of the high to the west,
but at the moment the most likely option is for it to "topple" over the UK
and into mainland Europe, restoring mild SW'lies. 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
The UK lies under a weak ridge with westerlies across all areas. Tomorrow
the ridge moves away eastwards and builds, leaving the UK under SW'lies.
There are further SW'lies for many on Tuesday and Wednesday, with a shallow
secondary low moving NE'wards across Scotland.

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 an exceptionally strong jet blasting across the
North Atlantic and the British Isles, with speeds approaching 200kt. At the
500hPa level there's a flat westerly gradient over the UK and upper lows to
the NNE and WNW. ECM and MetO also show a flat gradient, but they have the
upper lows further from the UK. NGP has an upper low over northern Scotland
and a strong westerly gradient aloft, while GEM and JMA also have westerly
gradients but with a slacker flow.
At the surface GFS brings a weak ridge and strong westerlies across the UK.
MetO has low pressure over Scotland and westerly gales elsewhere, while ECM
has a low over the North Sea and strong to gale force westerlies and NW'lies
as a result. NGP has a very deep low over NE Scotland with westerly gale or
severe gale force winds. The Canadian output also has strong westerlies for
most, although parts of Scotland escape due to a low to the west. JMA also
has a low in the vicinity of Scotland, with strong westerlies for England
and Wales.

Evolution to T+168
ECM shows a mobile but flat pattern aloft. On day 6 a trough approaches from
the west, bringing WSW'lies and SW'lies. On day 7 the trough crosses the UK,
bringing westerly gales for most. However, with pressure rising to the west
a NW'ly flow appears over NW Scotland and Northern Ireland.
GFS brings a similar pattern to ECM. On day 6 the UK lies under WSW'lies
with a low to the NW and a trough to the west. By day 7 the low moves
eastwards, dragging colder NW'lies over parts of Scotland and Northern
Ireland, with westerlies elsewhere.

Looking further afield
Beyond T+168, ECM shows a ridge to the west and NW'lies for all on day 8.
The ridge approaches the UK on day 9, bringing a mixture of WNW'lies and
NNW'lies. By day 10 the high "topples" over the UK, bringing NE'lies for
southern England and SW'lies elsewhere.
GFS shows a different evolution to ECM, with the high moving much more
quickly. On day 8 a ridge covers Ireland and it brings WNW'lies across the
UK. Day 9 sees strong to gale force SW'lies as the high moves over France.
On day 10 the high moves over eastern Europe, bringing strong (and very
mild) SSW'lies over the UK.

Ensemble analysis
(http://expert.weatheronline.co.uk/da...ia/ensdia.html - last
night's 18z)
The ensembles now show a lengthy mild spell next week, coming to an abrupt
halt next Sunday as colder air moves in from the NW. It's a two-day cold
snap, though, as temperatures aloft soon recover to above average values.