In message , Graham Easterling
writes
Must be around 6 or 7 degrees below normal, equivalent to freezing in
January or single figures in October? What's strange is that such an
ordinary looking west or northwesterly airmass should produce such low
temperatures - normally to produce temperatures significantly below
normal, a strong blast from the north or northeast or (in winter only)
east or southeast is required. Or fog...

NIck

The difference is that in summer the ocean to the west is a source of
relatively cold air while in winter it is a source of relatively warm air.
The ocean surface temperature to the west of the British Isles varies by
only a few degrees between summer and winter.

Norman.
(delete "thisbit" twice to e-mail)
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Not really quite right. The sea temperature off Cornwall at the moment is 16
degrees. The average annual range in recent years being 10 degres (8 - 18).

The warmest places yesterday were in Devon & Cornwall (south coast areas
18-20 degrees, 18.7 here in Penzance). So only 1-2 degrees below normal
here. If anything the nearby sea had a slight warming affect on the cold air
mass, the largest negative anomalies generally being inland.

Graham

I was talking about the ocean surface temperature i.e. the surface
temperature of the water beyond the continental shelf edge. I agree that
the surface temperature of the inshore waters can be very different and
the summer/winter variation is very much greater. The characteristics of
the maritime airmasses are determined partly by the broadscale ocean
surface temperatures and partly by airmass origin although, as you say,
there can be local modification resulting from inshore sea surface
temperatures.

Norman.
(delete "thisbit" twice to e-mail)
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Norman Lynagh Weather Consultancy
Chalfont St Giles 85m a.s.l.
England