Cloud cover on Ingleborough- explanation?

On Mon, 1 Oct 2007 22:38:49 +0100, "PeterK"
<[email hidden]> wrote:

... >At:
... > http://i230.photobucket.com/albums/ee6/peter_k_2007/IMG_2838_1.jpg
... >there is a picture (82k) of Ingleborough taken just after 22:00 tonight. The
... >moon has washed out what to the naked eye looks to be a distinct border
... >between the cloud "cap" and the lower slopes. (the bushes/trees also don't
... >help). I've seen this cap early in the morning in daylight and assumed it
... >formed as warm air started to rise and cooled.
... >
... >Any opinion on what causes it to form in the evening?
... >
... >PeterK

Cool air on warm ground ?

Mike P

In article <[email hidden]>, PeterK
<[email hidden]> writes

Quoted message said:

At:
http://i230.photobucket.com/albums/ee6/peter_k_2007/IMG_2838_1.jpg
there is a picture (82k) of Ingleborough taken just after 22:00
tonight. The moon has washed out what to the naked eye looks to be a
distinct border between the cloud "cap" and the lower slopes. (the
bushes/trees also don't help). I've seen this cap early in the morning
in daylight and assumed it formed as warm air started to rise and cooled.

Any opinion on what causes it to form in the evening?

It is from warm, stable air rising and cooling causing condensation as
wind passes over the hill. Once past the hill the air falls again,
becomes warmer and the moisture evaporates. Hence there is only a cloud
over the hill.

If the conditions are right they will form at any time day or night. In
the right conditions they can also form further clouds downwind of the
hill as the air rising over the hill then falling oscillates with the
peaks of the waves forming clouds and the troughs clear sky.

http://en.wikipedia.org/wiki/Lee_waves
http://en.wikipedia.org/wiki/Lenticular_cloud

--

Dominic Sexton

"Dominic Sexton" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

It is from warm, stable air rising and cooling causing condensation as
wind passes over the hill. Once past the hill the air falls again, becomes
warmer and the moisture evaporates. Hence there is only a cloud over the
hill.

If the conditions are right they will form at any time day or night. In
the right conditions they can also form further clouds downwind of the
hill as the air rising over the hill then falling oscillates with the
peaks of the waves forming clouds and the troughs clear sky.

http://en.wikipedia.org/wiki/Lee_waves
http://en.wikipedia.org/wiki/Lenticular_cloud

--

Dominic Sexton

Many thanks. Your opening paragraph certainly matches the scenario of a
cloud forming on the top and appear to be gently rolling over the edge.

Peter K

In message <[email hidden]>

PeterK said:

"Dominic Sexton" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

It is from warm, stable air rising and cooling causing condensation as
wind passes over the hill. Once past the hill the air falls again, becomes
warmer and the moisture evaporates. Hence there is only a cloud over the
hill.

If the conditions are right they will form at any time day or night. In
the right conditions they can also form further clouds downwind of the
hill as the air rising over the hill then falling oscillates with the
peaks of the waves forming clouds and the troughs clear sky.

http://en.wikipedia.org/wiki/Lee_waves
http://en.wikipedia.org/wiki/Lenticular_cloud

Quoted message said:

Many thanks. Your opening paragraph certainly matches the scenario of a
cloud forming on the top and appear to be gently rolling over the edge.

I suppose this
http://www.helvellyn.plus.com/pics/pics/glaramara/images/dscn0198.jpg
is similar. Although the cloud from a temperature inversion was
starting to spill over Sty Head, this particular part seemed to be
forming.

I've seen similar cloud caps form on top of Blencathra several times,
although not on nearby fells, so presumably it has beneficial
geography for this phenomena.

--
Simon Challands