Current air temperature +2.2°C, current grass temperature -3.3°C.
OK, nothing unusual about that.
Steady gentle breeze all night (8-12mph), minimum air temp +1.7°C (so far).
Moderate frost and ice on all concrete surfaces, including the roads. But
car windscreens are all frost free and covered in dew. Unusual to see such a
contrast between ground and air temperatures even on a calm morning at this
location, but this is rather bizarre with the breeze. I presume conditions
must be perfect for surface radiation - so why a such a selective frost
(cars are normally the first place I'd spot it)? Explanations please.
Alex

--
-----------------------------
Alex Stephens Jr
Wishaw, North Lanarkshire, Scotland
(20 miles ESE of Glasgow)
55°47'14" -3°55'15" 115m/358ftamsl
http://www.alex114.pwp.blueyonder.co.uk
----------------------------

In article ,
Alex Stephens Jnr writes:
Current air temperature +2.2°C, current grass temperature -3.3°C.
OK, nothing unusual about that.
Steady gentle breeze all night (8-12mph), minimum air temp +1.7°C (so far).
Moderate frost and ice on all concrete surfaces, including the roads. But
car windscreens are all frost free and covered in dew. Unusual to see such a
contrast between ground and air temperatures even on a calm morning at this
location, but this is rather bizarre with the breeze. I presume conditions
must be perfect for surface radiation - so why a such a selective frost
(cars are normally the first place I'd spot it)? Explanations please.

The only explanation that I can think of is that originally there was
ice on car windscreens as well, but then the temperature rose a little
and it had melted by the time of your observation. However concrete
would take much longer to warm up and so the frost persisted on it.
--
John Hall "George the Third
Ought never to have occurred.
One can only wonder
At so grotesque a blunder." E.C.Bentley (1875-1956)

On Sat, 22 Nov 2003 07:34:13 -0000, Alex Stephens Jnr wrote in


Current air temperature +2.2°C, current grass temperature -3.3°C.
OK, nothing unusual about that.
Steady gentle breeze all night (8-12mph), minimum air temp +1.7°C (so far).
Moderate frost and ice on all concrete surfaces, including the roads. But
car windscreens are all frost free and covered in dew. Unusual to see such a
contrast between ground and air temperatures even on a calm morning at this
location, but this is rather bizarre with the breeze. I presume conditions
must be perfect for surface radiation - so why a such a selective frost
(cars are normally the first place I'd spot it)? Explanations please.

Hi Alex

At the time you posted that it was +1.2C here, with plenty of frost on
ground and cars. The lack of frost on car windscreens your way must be
down to the wind, I think. In totally calm conditions, grass and car roofs
would behave in a very similar fashion with temperatures not far apart.
But that wind today would be moving *warm* air around the car top much more
than usual - keeping the top from cooling as much as usual. At grass level
that effect would be much reduced.

Still with frost on the grass here in Coleraine, so it looks like lasting
all day. Air temp is +5.1C.

--
Mike Coleraine posted to uk.sci.weather 22/11/2003 13:41:25 UTC
My aurora images here http://www.mtullett.plus.com/29a-oct and
http://www.mtullett.plus.com/20-nov/

Very strange, as cars are normally the first thing to show frost,
especially on the roof. Maybe the wind strength is in a critical range
(for the temperature) where it's sufficient to keep the cars above freezing but
nearer the ground the speed is low enough to allow the formation of frost.
An alternative would be that all the cars are being heated from the
inside by couples shagging. Maybe not.

Tudor Hughes, Warlingham, Surrey.

"TudorHgh" wrote in message
...
Very strange, as cars are normally the first thing to show frost,
especially on the roof. Maybe the wind strength is in a critical
range
(for the temperature) where it's sufficient to keep the cars above
freezing but
nearer the ground the speed is low enough to allow the formation of frost.
An alternative would be that all the cars are being heated from the
inside by couples shagging. Maybe not.

Tudor Hughes, Warlingham, Surrey.

Interesting alternative suggestion Tudor :-) - but alas I think the dew
would form on the inside of the cars and not the outside.
But I think I'll agree with the first answer you gave, it ties in with
Mike's answer.
I had no idea that such a difference between air and ground temp's (5.5°C)
was feasible in a breeze.

[OT]
Today is the 10th anniversary of keeping uninterrupted temperature records
for my site. Never thought I'd make it this far.
The very first day of those records, 22nd November 1993, was rather cold
with a maximum of only +1.1°C and a minimum of -6.8°C.
A quick look back through the archives at topkarten shows an intense
Scandinavian high with strong easterlies covering the UK, and 850mb temps
around -10°C for much of the country. Those were the days! :-)

Alex.