On Mar 4, 4:03*pm, Graham Easterling wrote:
On Mar 4, 3:02*pm, Dick wrote:





On Mar 4, 1:09*pm, Graham Easterling wrote:

Midday temperatures:-
2nd *7C * * (Eventual 0900-0900 max 8.4)
3rd * 12C * (0900-0900 max 12.4)
4th * 5C

The forecast was much the same for each day. The 7th saw a good deal
of sun, but the edge of the cloud was very close to the north. 3rd -
basically no cloud within 100miles. Today, sunny spells this morning,
but thicker cloud just to the south, breaking near the south coast.

A mainly blue slot now approaching so the temperature should rise 2 or
3 degrees soon. Much of southern/central Cornwall around 6-8C colder
than at same time yesterday.

Similar synoptics, very different weather.

Graham
Penzance

The temperature drop should have been expected Graham because
yesterday's midday output from the Met Office NAE model had shown a
cold pool moving westwards over northern France and the Channel today.
It predicted a drop of about 25 geopotential metres in the 1000-850mb
thickness over Cornwall between yesterday and today. Under cloudless
skies this would equate to a fall of 4C, but if you allow for about 5
or 6 oktas of cloud today, then the drop would be about 6C.

Dick Lovett- Hide quoted text -

- Show quoted text -

It was strange this wasn't taken into account in yesterday evening's
forecasts. E.g both the main forecast at 18:30 & the following local
forecast gave 12C max for Plymouth today. The previous evening they
had forecast 8C & it reached 13C! So completely the wrong way around.

I had noticed how low temperatures were at the Channel Light Vessel
yesterday afternoon, just 4C.

Graham
Penzance- Hide quoted text -

- Show quoted text -

A possible reason is that the temperature forecasts for towns & cities
are probably still derived from MOS data (Model Output Statistics)
where predictions of relevant parameters are compared, with the known
climatology of the location, via a statistical regression. I think the
method still relies heavily on model predictions of temperatures in
the 900-850mb layer. Camborne's midday ascents showed that both 900
and 850 mb temperatures were virtually the same on both days. The big
difference was in the much colder air below 900mb yesterday, which
would be accounted for in the thickness of the 1000-850mb layer.

Dick Lovett