December in Hamm is the windiest and the cloudiest month of the year. In December, the weather in Hamm is typically cold. Average daily high temperature in December is about 5 degrees above zero. On average, Hamm has 17 rainy, 10 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 Hamm.