You may have noticed that the changing thunderstorm climatology that ranges across the Dakotas eastward through Minnesota. Although large hail or torrential rainfall may occur from thunderstorms throughout the region, This is due to geography.
Westerly winds blowing off the tops of the Rocky Mountains create a layer of very dry air. When rain falls through this layer, some of it evaporates, causing a dramatic cooling, and a lower freezing level in the clouds. This is the primary reason that thunderstorms in the western Dakotas tend to produce less rainfall, but larger and more frequent hail. In fact, the area from southwestern North Dakota southward through western South Dakota into eastern Wyoming and northeastern Colorado is known as the hail capitol of North America.
