July in Rapid City is the hottest month of the year. In July, the weather in Rapid City is typically hot. Average daily high temperature in July is about 29 degrees above zero. On average, Rapid City has 16 sunny, 12 rainy, and 3 partly cloudy days in July. The rains are usually moderate. July as well as January, February, March, and April is considered the most uncomfortable time to visit Rapid City.