Darren Prescott wrote:
?Today marks the 9th anniversary of these model discussions - they
started as a look at the chance of a snowy Christmas back in 2001. The
first post can be seen on Google he
http://groups.google.com/group/uk.sc...689173fc?pli=1


Thank you to all readers over the years!

Here is a summary of the NWP output for noon on Tuesday.
Issued 0501, 10th December 2010

The models are split today. GFS keeps things much as it has for days,
with a strong NW'ly flow over the UK during the latter half of the week
and an increasing risk of snow both from showers over exposed coastal
areas and from troughs moving south. ECM offers an alternate solution,
with the original blocking high moving west and a new high setting up in
the vicinity of Scandinavia, with cold easterlies setting in (and an
increasing risk of snow in the east). Either way will bring cold weather
for the UK, but the areas affected by snow would be different in each
case. At the moment the GFS scenario has the most support model-wise but
it wouldn't be out of the question that ECM ends up being correct.

Analysis and evolution to T+120 via GFS
Westerlies cover the UK, with high pressure to the south and southwest
of the UK. Tomorrow the high rotates, bringing light winds to Wales,
Northern Ireland and SW England. Elsewhere winds are WNW'lies, followed
by NNW'lies for most on Sunday as the high declines to the NW. The high
builds again on Monday, moving to cover Scotland. Northern Ireland lies
under SE'lies as a result, with NE'lies elsewhere.

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 diffluent block over the Atlantic with the
UK on the warm side of the jet. The jet is exceptionally strong over the
Canadian Arctic and Greenland. At the 500hPa level there's an elongated
high stretching from Greenland SE'wards towards the UK, with a trough
over the SE of the UK. The upper flow is NNE'ly as a result, whereas
MetO shows northerlies aloft with a ridge to the west. ECM shows upper
northerlies too, with an upper ridge west of Ireland. GEM shows an upper
trough over the UK, with cyclonic northerlies aloft. JMA has NW'lies
aloft with an upper high to the NW rather than a simple ridge to the west.
At the surface, GFS brings northerlies with a large high to the WNW.
Southern England lies under NE'lies due to a shallow low over France.
MetO has NNW'lies for all with a high to the west, while ECM has a high
over Ireland and NNW'lies over the UK. GEM brings light winds due to a
col, while JMA has a col over England and Wales and northerlies elsewhere.

Evolution to T+168
ECM shows high pressure over England and Wales on day 6, leading to
SW'lies elsewhere. Day 7 sees southerlies for all as the high moves
eastwards.
GFS has NW'lies over the UK on day 6 as pressure remains high to the NW.
There are further NW'lies on day 7.

Looking further afield
On day 8 ECM brings SE'lies as pressure builds strongly over
Scandinavia. The winds become ENE'lies on day 9 as the high continues to
build and on day 10 NE'lies and ENE'lies cover the UK as the high builds
to over 1055hPa west of Scandinavia.
Day 8 with GFS brings yet more NW'lies as pressure remains high to the
west and NW. A trough moves southwards on day 9 and on day 10 low
pressure lies to the south, with easterlies and NE'lies over the UK.

Ensemble analysis
http://www.meteociel.com/cartes_obs/...&ville=Londres

The GEFS continues to show a milder weekend followed by prolonged cold.

ECM ensembles
http://www.meteogroup.co.uk/meteo/ep...tt6-london.gif
The ECM ensembles haven't updated since yesterday morning.


-------------------
Blimey, have we been here that long! Anyway, thanks as usual
for the brilliant reports which are the first read of the morning.
Cheers,
Dave