In Fairfax, Virginia, US, Kitty McCoy (Member 52,344) watched as strong updrafts caused a Cumulus congestus cloud (the tallest form of Cumulus) to build up in the sky. This skyscraper of a cloud was the first stage in a larger development: becoming a Cumulonimbus calvus, the powerful storm cloud that can produce heavy rain, hail, wind, and lightning.

‘A few minutes later,’ Kitty told us, ‘the storm cloud under construction was complete, and the heavens opened up with torrential rain.’