The wettest month of the year is August, with an average 4.03 inches (102 mm) of precipitation, mainly as rainfall. Long-duration rains are uncommon in summer, usually occurring only in April or October. Thunderstorms are the main precipitation events from May until September, and Milwaukee experiences an extended tornado season that lasts from late March until early June, however, severe weather and tornadoes are more frequent inland to the west. The driest month is February, when only 1.65 inches (41.9 mm) of precipitation falls, almost entirely as light, low moisture content snow resulting from the Alberta clipper type system when cold, dry air masses dominate.