Graham P Davis wrote:

On 09/07/17 13:18, Ron Button wrote:
Just watched that giggly woman on BBC news channel having showed the radar
picture for the UK which shows a large area of cloud covering much of
Eastern England followed by the usual warning to slap on high factor
sunscreen because of the strong sunshine Having seen the heavy Cu build up
to virtually 8/8 cover here in the south-east since late morning ,what
could possibly cause this overcast to dissipate and therefore come into
line with what is obviously an incorrect forecast ?



I was told years ago that UV levels when Cu is around can be higher than when
there is no cloud. I think what happens there is that you get a lot of
reflected radiation.

Another point is that I assume the cloud was CuSc (I haven't really been
noticed as I've been watching the cricket) as you can't really have more than
4/8 cover of Cu. It may look like more but, when assessing the amount of Cu,
you have to ignore the sides of the cloud and merely add up the area of the
bases.

If you've got a ruddy great Cu sitting right on top of you with a base at 800ft
and it's peeing down with rain then I think it's reasonable to call it 8/8 Cu
:-)

--
Norman Lynagh
Tideswell, Derbyshire
303m a.s.l.
http://peakdistrictweather.org
Twitter: @TideswellWeathr