"Len Wood" wrote in message
...

On Nov 23, 2:27 pm, Hugh Newbury wrote:
The BBC Bristol weatherman said last night that the lowest temperature
this morning would not be just before dawn, but just after. He didn't
have time to explain why, so could someone here please help me see why
this should be.

TIA

Hugh
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Hello Hugh,

Ken's explanation is probably the main reason why temperatures don't
rise immediatedly at sunrise,
but there is another factor, transport of cold air, that can delay the
rise in temperature and even produce the legendary 'post dawn
freeze'.
This is highly dependent on locality.
After sunrise when the solar flux is sufficient to warm the surface,
the surface temperature inversion begins to erode.
This allows movement of any surface air which might have been trapped
in cold air pools or frost hollows.
It is likely to drain to lower land, producing a temporary dip in air
temperature.

Hi, Len,
It has the effect here of stopping the overnight katabatic which has kept
the temperature higher. The resultant calmer air allows rapid cooling for a
short time before the sun takes over. During, clear, calm light wind
situations, we have the lowest temperatures just before the katabatic sets
in and stirs things up, around an hour after sunset, and again just after
the katabatic stops. Most of the night is too windy for any lower readings.
It's a question I have been asked more than once. In marginal situations,
car windscreens can be damp at sunrise and frozen 30 minutes later!
Best wishes,
Ken