August in Arosa is the sunniest month of the year. In August, the weather in Arosa is typically warm. Average daily high temperature in August is about 14 degrees above zero. On average, Arosa has 18 rainy, 11 sunny, and 2 partly cloudy days in August. The rains are usually heavy. August as well as April, May, June, and July is considered the most uncomfortable time to visit Arosa.