August in Nagano is the warmest month of the year. In August, the weather in Nagano is typically warm. Average daily high temperature in August is about 24 degrees above zero. On average, Nagano has 26 rainy, 4 sunny, and 1 cloudy day in August. The rains are usually heavy. August as well as March, April, June, and July is considered the most uncomfortable time to visit Nagano.