------ Forwarded message ------

On Dec 5, 6:59 pm,

[Snip]

GFS DT12Z 4/12/09

Shows battle lines drawn by as early as next Saturday. As suggested
by the ensembles earlier this week a deep Atlantic low throws up a
ridge over Britain on Thursday and then this merges with the Russian
high containing extremely deep cold air and the density easterly
current surges westwards as I expected yesterday. Britain could be
in a very wintry setup as early as next weekend. As this is backed
up by previous ensemble runs and consistent dynamics I'm getting
more confident. Expect a few more flip-flops of course and the cold
may yet stay just to the east of us but we will be entering a
different weather regime after less than a week from now.

Looks that way, Will. By next Friday EC's 12Z operational run has
developed a strong upper block over western Europe. Even if there's
not cold air in depth by then the low level flow into the UK could be
quite chilly. Will be interesting to see how this fits with the
midday ensemble data.



12Z ensembles are rocking and rolling Jon. Party on!

No real change today. As Darren says a change in the weather later next
week is practically certain. What interests me is the consistent and
strong development of a northern block, predicted by some models last
month. This is feeding sub 492 DAM air into Russia which will filter
west as a density current and could take many by surprise. Even next
weekend we are looking at below normal temperatures in the UK with
night frost. Ensembles still suggest that a cold or even very cold
spell is on the cards. Even at T+240 the Spaghetti plots are more
confident than normal showing an upper high over Britain with a very
cold trough over Russia. The ensemble mean is now beginning to show a
developing low pressure region over Poland which will strengthen more
any very cold easterly. Next week is going to be most interesting
watching how this is all going to pan out.

--

DT 12Z ECM 5th is showing an omega block developing centred over Britain
extending into the Arctic next Sunday/Monday with bitterly cold air (sub
492 DAM) to the east. That model is consistent with 12Z GFS ensembles and
with itself in a time-lagged sense. Weather regime change is on the way!

Well, I don't know Will! It's not the battleground between east and
west that was promised for a short time last weekend. That was a
classic battle between an easterly flow, around a Scandinavian high
and the Atlantic fighting from the West and it's outcome date would
have been the 11th Dec. The gfs now shows (and has I think shown for
48 hours - though sorry I haven't been able to comment through
yesterday and this morning)) the development of a high to our south at
T96, which drifts northwards over the UK and then settles just to our
SE. After it does, an omega block forms, as heights finally begin to
rise over Scandinavia. There is a possibility that this will drag in
cold air at T240+, but I'd need another 3/4 runs and agreement with
the ECM to forecast that cold air would approach the UK and not sink
towards Greece.

On the other hand, the ECM 00z showed a very odd and uncharacteristic
development at T168 with a "sausage" high over Scotland, stretching
into the Atlantic and dragging easterly air over the UK as soon as
next friday/Saturday. On the 12z ECM, a high is now shown developing
over Spain and drifting northwards to sit to our SE by T144. Pressure
is then shown to rise over Scandinavia and to join with this high and
though this could have a cold effect on the UK, it's a long way off
and not shown as fully enveloping us, even at T240.

The development is similar on both models and the possibility of this
developing fully into an omega block can't be discounted. i.e. there
are possibilities of a cold NE/E flow into the second half of
December, but I feel it is by no means as certain as you do! Again,
this has nothing to do with an original Scandinavian high and a
classic W/E UK battleground by the 11th. Yesterday morning the models
changed to show the development of high pressure over the UK at around
9 days. I was actually on the brink of a forecast of SW winds, at 10
days, last Thursday evening (i.e. next Sunday). The change shown on
Friday lowered the possibility of that forecast.

There is a chance of colder air being drawn across the UK from the
east during the 3rd week of Christmas, but you are brave man for
having forecast it Will!

------ End forwarded message ------

--
Rodney Blackall (retired meteorologist)(BSc, FRMetS)
Buckingham, ENGLAND
Using Acorn SA-RPC, OS 4.02 with ANT INS and Pluto 3.03j