The leading edge of the downdrafts produces a gust front near the surface. As the gust front passes, the wind on the surface shifts and becomes strong with gusts exceeding 100 kilometers per hour, temperatures become cold, and the surface pressure rises. Warm moist air that rises over the gust front may form a roll cloud . These clouds are especially prevalent when an inversion exists near the base of the thunderstorm. Model of the major features and circulation patterns associated with a severe thunderstorm.
Some severe thunderstorms develop a strong vertical updraft, commonly known as a mesocyclone .
Mesocyclones measure about 3 to 10 kilometers across and extend from the storm's base to its top. They are also found in the southwest quadrant of the storm. About half of all mesocyclones spawn tornadoes. When a tornado occurs, the mesocyclone lengthens vertically, constricts, and spirals down to the ground surface. Scientists speculate that mesocyclones form when strong horizontal upper air winds interact with normally occurring updrafts.