Why do flat areas have so many tornadoes?

A more accurate answer. Contrary to popular belief, tornadoes can pass over mountains and valleys without weakening. However, rough terrain can disrupt the ability of storms to organize, making it more difficult for tornadoes to form. Mountains can also block the movement of moisture necessary for storm formation in what is called the rain shadow effect. That tornadoes are so common on the Great Plains has more to do with climate than with topography. There is also a bias created by our ability to photograph tornadoes Major tornado outbreaks are not uncommon in hilly areas of Kentucky, Tennessee, and Alabama, but the tornadoes in this region are often shrouded in rain or blocked from view by hills and trees, resulting in fewer photographs. By contrast, the tornadoes of the Great Plains are less likely to be blocked from view, providing ample opportunity for clear pictures.