December in Mannheim is the rainiest and the windiest month of the year. In December, the weather in Mannheim is typically cold. Average daily high temperature in December is about 5 degrees above zero. On average, Mannheim has 18 rainy, 9 cloudy, 3 sunny, and 1 partly cloudy day in December. The rains are usually moderate. December as well as January, February, and November is considered the most uncomfortable time to visit Mannheim.