Merry Christmas, Daren, and thank you for your excellent summaries.

--
Bernard Burton
Wokingham, Berkshire, UK.

Weather satellite images at:
www.woksat.info/wwp.html

"Darren Prescott" wrote in message
o.uk...
Here is a summary of the NWP output for noon on Tuesday.
Issued 0519, Christmas Day 2009.

**Merry Christmas to all readers!**

The battle alluded to yesterday will still be raging in the middle of the
week. Low pressure to the SW will be moving towards the UK, with mild air
entrained. Cold air over Scotland will be sinking slowly southwards and
where the two meet there'll be heavy rain, with snow on the northern edge.
At the moment, that location is still uncertain, ranging from the Scottish
borders (ECM) to the Midlands (GFS).

During the latter half of the week, the cold air will very slowly sink
southwards, with the snow risk transferring southwards too. Low pressure
will be close by to the south throughout, so the potential is there for
some
significant snow and drifting in the strong winds, especially over high
ground. GFS goes a step further and brings genuine blizzards across much
of
England and Wales on New Year's Day, but it's most unlikely to verify
exactly like that at this range.

Into the New Year we have a blocking upper high near Greenland and it's
unlikely to warm up for a fair while; indeed GFS shows a prolonged
countrywide cold and snowy spell. However, bear in mind it's Christmas
Day -
GFS may not be quite as reliable as normal due to somewhat lower data
counts. It's worth staying tuned to Met Office forecasts over the coming
week as the situation evolves. A couple of hundred miles either way would
make a massive difference!

Analysis and evolution to T+120 via GFS
Northerlies cover much of the UK with low pressure over Benelux. Tomorrow
sees SE'lies for most as low pressure fills to the west, although winds
are
light over the snowfields of Scotland due to a col. On Sunday a trough
moves
eastwards with SSW'lies for all in advance. Monday sees a col over the UK.

T+120 synopsis
http://91.121.93.17/pics/Rtavn12015.png /
http://91.121.93.17/pics/Rtavn1201.png
http://91.121.93.17/pics/Rukm1201.gif
http://91.121.93.17/pics/Recm1201.gif /
http://www.meteociel.fr/modeles/nogapse_cartes.php
The jetstream chart shows a complex pattern. There's a strong and rather
zonal southerly jet over the Azores, Iberia and southern Europe, with a
weaker and more fragmented northern branch looping over Greenland and
heading south to the west of the UK. At the 500hPa level there's an upper
trough for the UK, with a cut-off high building south of Greenland. ECM
shows a westerly flow aloft with an upper ridge building towards
Greenland,
whilst MetO brings upper westerlies too with a broad westerly flow across
western Europe. GEM shows westerlies too, as does JMA.
At the surface, GFS brings NE'lies with a low to the SSW and a trough over
the Channel. ECM shows ESE'lies, again with a trough over the Channel.
MetO
brings easterlies and WNW'lies with yet again a trough over the English
Channel. GEM and JMA have a trough over northern France. In GEM's case, a
ridge brings NNW'lies to Scotland and Northern Ireland, with easterlies
elsewhere; JMA shows ENE'lies for all.

Evolution to T+168
ECM shows strong ENE'lies on day 6 with lows to the SE and SW. The lows
merge to the south on day 7, with strong (and in the north, cold) NNE'lies
for the UK.
GFS brings a low to the south and strong NNE'lies on day 6. The low fills
and moves along the English Channel on day 7, bringing strong to gale
force
easterlies and northerlies. As there's cold air across much of the UK by
then, widespread blizzards would result (away from the far SE, perhaps).

Looking further afield
ECM shows northerlies on day 8 with lows to the east and ESE. On day 10 a
col covers the UK, as the low to the east crosses the UK. By day 10 a
ridge
brings light winds for many.
GFS has northerlies for all on day 8, with low pressure to the west and a
large blocking high near Greenland. Strong NNW'lies cover the UK on day 9
as
low pressure moves south over Scandinavia. Day 10 sees strong, unstable
NNW'lies with some very cold air aloft moving southwards.

Ensemble analysis

(http://91.121.94.83/modeles/gens/gra...y=141&run=0&vi
lle=Londres)
The ensembles show a relatively mild few days ahead, followed by an abrupt
shift to a prolonged cold spell.