August in Mammoth Lakes is the sunniest month of the year. In August, the weather in Mammoth Lakes is typically warm. Average daily high temperature in August is about 24 degrees above zero. On average, Mammoth Lakes has 26 sunny, 3 rainy, and 2 partly cloudy days in August. The rains are usually light. August as well as September is considered the most comfortable time to visit Mammoth Lakes.