Based on the context and the answer, generate a question. 

Context: And looking out of the windscreen , we saw something I ' ve never seen before : a sort of limp sausage - shaped cloud sticking out of the side of a thunderhead , hanging down towards the Shannon Estuary . It looked like a cloud with a ponytail . Odd thing . The twisting of the tip hanging down made it more obvious , though : it was a tornado !

Answer:

They were having a storm while it was hot outside .



What may have caused the tornado ?