Northern hemisphere tornadoes occur when cold dry air from the north meets warm humid air in the south. The south has warm humid air most of the year, so the key ingredient is the cold air. That is why April has more tornadoes than July – when the air is warmer and more humid.
Global warming theory requires that the Arctic warms, which means less cold air to form tornadoes. People who claim that global warming brings more or stronger tornadoes, are scientifically illiterate. Which of course is the norm for climate experts.