On Sep 11, 8:34*am, Dawlish wrote:

Well the Meto is hedging its bets, but this forecast was issued at
lunch yesterday and, as usual in the morning, is a day out of date.

"UK Outlook for Tuesday 15 Sep 2009 to Thursday 24 Sep 2009:
Much of the country will remain dry through the middle of next week
and over next weekend, but with variable amounts of cloud. Some sunny
spells are likely, more especially in the southwest of England and
Southwest Wales at first. The far Northwest of Scotland could see a
little little rain at times, with also a small risk of showers
extending into far south and southeast of England. Temperatures in all
parts should be near normal, and feeling pleasant in sunshine.
**Southern and Central parts should start mainly dry and fine in the
longer outlook, but there is a low risk of it turning more unsettled
with time. The Northwest is expected to turn more unsettled with
occasional showers or rain.**"

Updated: 1201 on Thu 10 Sep 2009

That's also an interesting comment in the 6-15 day forecast because
that phrase gives an insight into the forecaster's thinking - more
likely to continue settled over England, but a chance of it not doing
so. It also reflects my thinking that an actual forecast would have
less than a 75% chance of being correct.

Therein lies the current problems of forecasting at 10 days. It really
is very difficult.

Really very interesting....

The high pressure will still be in charge tomorrow Sunday, with a
front skirting around the northern limb of the high, then slipping
down the North Sea to introduce cloud into some Eastern areas - but
then look at how the forecast has changed next week. A strengthening
north-easterly flow in the south is likely to bring cloud (and speak
it in a whisper) a little rain to the SE (!) as southern areas come
under more of an influence from a large area of low pressure over the
Med. It is likely to be a change which I don't think was possible to
forecast with accuracy, even 6 days ago, never mind 10.

On Sept 11 (see above), the MetO had "Southern and Central parts
should start mainly dry and fine in the longer outlook" i.e. high
pressure would still be in charge in those areas on 17th to (say) 19
Sept (at 6-8 days from the forecast date). That's now unlikely and the
"low risk" of it turning unsettled with time looks like it will happen
well before that 6-15-day forecast was implying, ruining any outcome
accuracy for that forecast. Even at 6 days, the forecast is now much
more likely to be proved incorrect, than correct.

That's why I didn't forecast the high pressure dominance continuing
further than Sunday, but I admit I couldn't see this change next week
at 10 days. All I could see was that there was not enough model
agreement for anticyclonic, settled and fine weather, continuing to be
75% likely. The actual situation in mid-week next week was one that I
feel was not possible to forecast with any current capability, except
by guesswork and the change came well below my 10-day radar.

Out at T240, the gfs has unsettled and the ECM has higher pressure
with an anticyclone again building. You pays your money and you takes
your chance on that one.