A sobering thought about Cu's topping out at FL100.....
Whilst I was undertaking flight training in the States a few years ago a particularly nasty tornado wreaked havoc in the Kansas area.
Although this happened hundreds of miles away, I was interested in what sort of storm would cause this sort of damage.
Having made some enquiries, you may be surprised to know that the linesquall CBs involved topped out at no more than 12500' or thereabouts. (I had some copies of doppler radar images showing the perfect "hook" shape in the middle of the returns, but lost them in a house move sadly.)
I know that the weather in the UK is different to the US, but it does make you think....