On Wed, 13 Feb 2013 16:57:43 -0000
"Eskimo Will" wrote:
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.
=========================
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.
It suggests that the snow-line has changed very little in height over
several days; if it had moved up and down more, the change in snow
cover in the vertical would have been much more gradual.
--
Graham P Davis, Bracknell, Berks.
Feeling stressed and frustrated? Try a short session of contemplative
meditation. Or kick a ballboy. (
https://twitter.com/GreySkyThinking)