August in Des Moines is the sunniest month of the year. In August, the weather in Des Moines is typically warm. Average daily high temperature in August is about 27 degrees above zero. On average, Des Moines has 23 sunny, 6 partly cloudy, and 2 rainy days in August. The rains are usually light. August as well as September is considered the most comfortable time to visit Des Moines.