May in Ulm is the rainiest month of the year. In May, the weather in Ulm is typically warm. Average daily high temperature in May is about 16 degrees above zero. On average, Ulm has 21 rainy, 8 sunny, and 2 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 Ulm.