On Wed, 30 Aug 2017 02:51:00 -0700 (PDT)
Freddie wrote:

On Wednesday, 30 August 2017 09:29:47 UTC+1, wrote:
Only last night they were predicting heavy rain for kent this morning and
moderate rain for London and the rest of the SE. Actual weather? Nothing of
the sort. A few scattered patches of drizzle with the main rain band way
off in Belgium. How can they get it so wrong only 12 hours in advance? Did
the wind suddenly turn 90 degrees overnight?
Nothing to do with the wind direction (as you present it) and everything to
do with the way small variations in shape and speed within the jet interact
with the moisture in the lower and middle troposphere. Tiny errors in
analysis have a massive impact on the end result - and the impacts change
dramatically in a very short period of time. The forecasters know their
stuff, it's just they sometimes can't keep up with the changes.

Never forget that the atmosphere is a complex three-dimensional beast that
would be almost totally unpredictable without computer models.

Having said all that, I agree that it was a poor forecast. The only way
handling of these situations can improve is through better modelling (more
horizontal and vertical resolution, and more responsive assimilation of
current data) which will enable a better response to when the forecast looks
like going adrift.


Better communication of uncertainties would help too.

Will
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