"GKN" wrote in message
news
Hi Will.
I am not sure as to its actual thickness, but it looked at times that it
should have been pouring with rain. Lets say I have seen heavier rain with
the sun shining through thinner cloud.

This doesn't answer your question but I have often noticed that
with an approaching front the cloud needs to build up to a
great thickness (based on darkness) before any rain falls
Conversely as the front pulls away there can stil be moderate
rain falling when the sky is really quite bright, even with fleeting
glimples of the sun.
--
Col

Bolton, Lancashire
160m asl