Hmm, I've seen tornado paths that have scoured the ashpalt and concrete roadway fairly completely. I would much prefer to get below grade a few feet if possible. Unfortunately here in Florida nearly all residential is without a basement due to the amount of water in the ground, at least from what I've seen here just north of Orlando. We had a tornado scare just before Xmas here, and I was left with the prospect of putting the whole family in the guest bathroom tub surround. Not what I'd call secure. I am told that the tornadoes that do touch down here are not too strong, typically iF0 or iF1 at most. iF5's are the road rippers I guess.