August in Wisconsin Dells is the sunniest month of the year. In August, the weather in Wisconsin Dells is typically warm. Average daily high temperature in August is about 25 degrees above zero. On average, Wisconsin Dells 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 Wisconsin Dells.