Hello everybody,
While Gatwick last night had fog and frost (-3°C), up here on the Downs
12 miles to the NNE we had a steady 8-10 mph SSE'ly and a minimum temperature
of 3.0°C, sky clear throughout. There was quite heavy frost on some pavements
but, with the breeze, none on cars. Even Heathrow got down to 1°C with shallow
fog. Another interesting feature was the difference in the wind directions; at
Gatwick ENE 1-2 kt, and Heathrow it backed right round to NE 2 kt, both of
which are more than 90° from the isobars. The wind was thus moving against the
pressure gradient, especially at Heathrow. It can hardly have been a katabatic
effect - Heathrow is dead flat. We all know the wind is markedly backed from
the isobars at night especially with an inversion present, but this seems
extreme. Anyone any ideas?

Tudor Hughes, Warlingham, NE Surrey, 556 ft AMSL.

"TudorHgh" wrote in message
...
Hello everybody,
While Gatwick last night had fog and frost (-3°C), up here on the
Downs
12 miles to the NNE we had a steady 8-10 mph SSE'ly and a minimum
temperature
of 3.0°C, sky clear throughout. There was quite heavy frost on some
pavements
but, with the breeze, none on cars. Even Heathrow got down to 1°C with
shallow
fog. Another interesting feature was the difference in the wind
directions; at
Gatwick ENE 1-2 kt, and Heathrow it backed right round to NE 2 kt, both of
which are more than 90° from the isobars. The wind was thus moving
against the
pressure gradient, especially at Heathrow. It can hardly have been a
katabatic
effect - Heathrow is dead flat. We all know the wind is markedly backed
from
the isobars at night especially with an inversion present, but this seems
extreme. Anyone any ideas?

A heat low (or troughing) over central London? You need a mesoscale
analysis, really, rather than just two obs, to get much further.

Philo