September in Bol'shaya Seya is the sunniest month of the year. In September, the weather in Bol'shaya Seya is typically warm. Average daily high temperature in September is about 12 degrees above zero. On average, Bol'shaya Seya has 13 rainy, 12 sunny, and 5 partly cloudy days in September. The rains are usually light. September as well as January, February, April, and May is considered the most uncomfortable time to visit Bol'shaya Seya.