It's chance. Do you actually believe that we haven't had tornadoes for as long as we've had an atmosphere? No matter what the Carbon Cult claims: humans don't control the weather.
We will have tornado swarms again just as we have had in the past. Instead of wasting resources on the impossible task or altering our climate we should increase funding for tornado detection and warnings.
In the mean time, stop building stick houses in harms way. Build underground.