May in Heidenheim is the rainiest month of the year. In May, the weather in Heidenheim is typically warm. Average daily high temperature in May is about 16 degrees above zero. On average, Heidenheim 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 November is considered the most uncomfortable time to visit Heidenheim.