wrote in message
...
I have been struck over the last few days by the huge difference between
snow cover at the top of Hampstead Heath (380 feet ASL) and nearby but
slightly lower locations such as Swiss Cottage. Although the top of the
Heath is generally a little snowier than nearby lower spots, for the recent
snow event the difference has been remarkable. At the top of the Heath near
the car park behind Jack Straw's Castle, the snow depth has been a
consistent 5-8cm since Monday morning (11th) with trees and shrubs plastered
in snow even until this morning. It is a true winter scene. Only a few
hundreds yard away where we live at a height of about 250 feet, the snow has
been 2-3 cm in depth with the trees losing their cover from Tuesday. Down in
Swiss Cottage, no more than 1.5 miles from the top of the heath at a height
of about 180 feet, there is now scarcely any snow to be seen. Other parts of
London are now similarly snowless. I presume the difference is attributable
to a combination of the lapse rate, orographic uplift and fewer buildings.
Still, it is rather remarkable given the relatively small altitude
differences involved.

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Yes it is called the "snow line" for good reason. It actually is a
horizontal line. More noticeable admittedly in very hilly/mountain areas but
will be there at an level. Last month the snow line in my area was at circa
100 metres asl, today it would be above the summits. Cities do add a
complication as you suggest in that the additional urban heat will tend to
melt snow faster obviously. Above the snow line amounts will vary depending
on where the wet-bulb freezing level was when it started snowing. The
deepest snow will be from 100 metres above the wet-bulb freezing level
upwards. Fascinating post, many thanks. It will be all gone by this time
tomorrow though.

Will
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http://www.lyneside.demon.co.uk/Hayt...antage_Pro.htm
Will Hand (Haytor, Devon, 1017 feet asl)
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