May in Grenoble is the rainiest month of the year. In May, the weather in Grenoble is typically warm. Average daily high temperature in May is about 15 degrees above zero. On average, Grenoble has 18 rainy, 9 sunny, and 4 partly cloudy days in May. The rains are usually heavy. May as well as January, February, March, and April is considered the most uncomfortable time to visit Grenoble.