That's usually when they're prominent, actually. Tornadoes don't always strike when it's ugly, raining and lightning out. It may storm really bad, but then it will stop, THATS when you have to worry. Or when it's REALLY NICE out but theres a bad storm front moving in... maybe you just missed the front?

I know it's prime when it's warm and sunny and then a huge cold front will move in, PRIMEEE breeding ground for tornadoes.