June in Sion is the rainiest month of the year. In June, the weather in Sion is typically warm. Average daily high temperature in June is about 16 degrees above zero. On average, Sion has 20 rainy, 5 sunny, and 5 partly cloudy days in June. The rains are usually heavy. June as well as April, May, July, and August is considered the most uncomfortable time to visit Sion.