September in Washington is the sunniest month of the year. In September, the weather in Washington is typically warm. Average daily high temperature in September is about 24 degrees above zero. On average, Washington has 15 sunny, 9 partly cloudy, 5 rainy, and 1 cloudy day in September. The rains are usually moderate. September as well as {{month_nom: February}}, and {{month_nom: February}} is considered the most comfortable time to visit Washington.