The region of greatest tornado activity shifts northward from early spring to summer. why does this occur?

The region of the greatest tornado activity shifts northwards from early spring to summer because the cold air reaches the boundary for expansion at the Gulf and as spring approaches, the days grow longer which allows for more heating from the sun. When this happens the temperatures on the ground will typically go up, and the warm, moist air from the Gulf of Mexico will push the cold air back up. During this time of activity the region for this sever weather area will move eastward around the southeastern Atlantic states. During this time the southeastern Atlantic states will have a peak of activity around April. When the spring air advances, the region for tornado activity will gradually shift to the west and will eventually then move northward.