During the winter, severe hailstorms are generally restricted to the Southeast. Most activity occurs in a band from east Texas to north Alabama. Meteorologically, this is a reflection of the relatively cool temperatures across the continent, the general lack of moisture in the air anywhere but along the coast of the Gulf of Mexico, and the low sun angle that limits the area of insolation sufficient for thunderstorm development. In April, the sun angle and length of daytime heating increases and moisture returns northward due to the strengthening of the Bermuda High. This, in concert with northward migration of the jet stream, shifts the maximum hail area to Oklahoma and the Red River Valley.
Continued northward progression shifts the July maximum to the Plains from eastern Colorado to northern Minnesota. There is also a weak summer maximum in smaller hail sizes over the desert southwest, indicating reports from hailstorms occurring with the North American monsoon. The northwestern states also have a small signal during this period, as extreme heating along the sloping terrain during the summer months helps to produce instability over this region leading to some severe hail producing storms. A small July area of enhanced hail activity is also located in Central Florida in the area where the Atlantic and Gulf of Mexico sea breezes often interact. Over the rest of the Southeast, except for along the Appalachians, hail activity during the summer is suppressed by the warm troposphere. In the autumn, the severe hail activity pattern is quite similar to the spring pattern. However, the occurrence rate is greatly diminished.