On 23 June, 00:14, Tudor Hughes wrote:
On Jun 22, 5:51*pm, "Darren Prescott"
wrote:



I note with some trepidation that GFS has been gunning for some very high
dewpoints in the coming week. In the 12z GFS, that reaches a ridiculous
extreme in a week:

http://i43.tinypic.com/sq5cba.gif

If that were to come off there'd be no end of moaning from Joe Public.

As a side note, it's been pleasant here in Kent, with dewpoints in single
figures this afternoon. A stark contrast to the rest of the UK, with the
Bristol area for example "enjoying" dewpoints of 17 or 18C as I write this.

I was going to ask where all this moisture has come from, seeing that we
have an easterly flow, it's not been especially wet in the past few days and
the sea's not even 15C. However, checking the archives I see Tudor Hughes
asked the same question back in 2003 - and the consensus then was that it
was evapotranspiration.

* * * * Dewpoints in the southeast are falling at the moment
(typically 9°C at midnight) but are higher further west due to the
origin of the air as pointed out by Martin Rowley. *I think
evapotranspiration always has quite a large effect in summer, there
being really no other way of explaining why the dewpoint rises during
the day and and can sometimes exceed the sea temperature at the
airmass's origin.
* * * * *I see the latest GFS has toned it down considerably and it
makes me wonder how they arrived at the original sauna conditions.
Living in a climate where the actual weather was GFS T+168 would be a
bizarre and unsettling experience.

Tudor Hughes, Warlingham, Surrey.

It always amazes me how mid-20s dewpoints get into the heartland of
America considering the distance from the sea. I realise that air
originates in Gulf of Mexico with 25-30 C SSTs but there seems to be
no loss due to the usual condensation processes (rainfall, dew).

Martin