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 !
According to the above context, answer the following question.
What may have caused the tornado ?


They were having a severe thunderstorm .