September in Black Rock is the hottest month of the year. In September, the weather in Black Rock is typically hot. Average daily high temperature in September is about 28 degrees above zero. On average, Black Rock has 22 rainy, 4 cloudy, 2 sunny, and 2 partly cloudy days in September. The rains are usually heavy. September as well as January, June, July, and August is considered the most uncomfortable time to visit Black Rock.