April in Rapid City is the windiest month of the year. In April, the weather in Rapid City is typically warm. Average daily high temperature in April is about 10 degrees above zero. On average, Rapid City has 12 rainy, 9 partly cloudy, 7 sunny, and 2 cloudy days in April. The rains are usually moderate. April as well as February, March, and May is considered the most uncomfortable time to visit Rapid City.