On Wednesday, 11 April 2018 12:59:13 UTC+1, Graham Easterling wrote:
Around noon, as the temperature rose, a north coast sea breeze developed around St Ives / Hayle. The gradient E wind veered more SE in Penzance due to the south coast sea breeze effect. A Cb rapidly developed just behind Penzance, giving a few large drops of rain, seemed to be pretty heavy just inland. It was then carried away over the Atlantic.

Quite interesting if not that exciting!

I find it interesting. I've just watched a loop of satellite imagery and saw the rapid development of the CB before it was whisked off out into the Atlantic. It appears that there was an area of moister air at medium levels crossing you at the time. This has moved away west now, and you appear to have drier air now at that level. Just goes to show that you required a juxtaposition of several factors - pre-existing unstable air, low level convergence and some moisture at medium levels - before a CB would form on a marginal day such as this. Who would be a forecaster!

Thanks for highlighting something I otherwise would've missed.

--
Freddie
Ystrad
Rhondda
148m AMSL
http://www.hosiene.co.uk/weather/
https://twitter.com/YstradRhonddaWx for hourly reports (no wind measurement currently)