September in Denver is the sunniest month of the year. In September, the weather in Denver is typically warm. Average daily high temperature in September is about 23 degrees above zero. On average, Denver has 27 sunny, 2 partly cloudy, and 1 rainy day in September. The rains are usually light. September as well as {{month_nom: February}}, and {{month_nom: February}} is considered the most comfortable time to visit Denver.