"Tudor Hughes" wrote:

On Jul 2, 11:59 am, "Togless" wrote:
Looking north from my house here in Portsmouth I can see large grey
clouds
looming up rather quickly, and on the satellite photos it has all
developed
just in the last 2 hours or so - what is that called, when (presumably)
the
heat of the sun makes the sky go from clear blue to masses of cloud in
just
a couple of hours? Anyway, I'm hoping that an onshore breeze will keep
it
away from us here on the coast. Sometimes being on the coast works in
our
favour, and sometimes not (sea mist etc).

John.

It's convection over the heated land. The air will cool as it
rises and will form cloud when it reaches saturation. Today it won't
rise very far because there is warmer air aloft so the cloud spreads
out. We have similar cloud here.

Thanks Tudor - I knew about the first part, but hadn't appreciated the
second. What do you use to determine that there is 'warmer air aloft', if
you don't mind me asking? Presumably in different circumstances you would
get large high cumulus clouds and the risk of intense precipitation - is
that right?