Rain shadows are caused by the mountains. Asheville is in one — it’s actually the driest city in the state. That is why they moved Asheville’s official weather station out to the airport, where it would be more representative of the area. When moisture-laden air comes from the west-southwest, it hits the mountains. It leaves a lot of moisture on the west side, but when it tops the mountains it gets a little bump and skips over Asheville before dumping the moisture a little bit farther east or north.
Millions of years ago America and Africa rubbed shoulders and the Appalachian Mountains were created. The ancient Appalachians, at one time as high as the Alps or Rockies, created quite an east-west barrier from Canada down to central Alabama. Today’s kinder, gentler Appalachians eroded and for the most part still impact us in myriad ways. A lot of it has to do with weather. As most of our weather patterns come from the west, we on the east side of the Appalachians often have to wait and see what we get.