December in Slany is the windiest month of the year. In December, the weather in Slany is typically cold. Average daily high temperature in December is about 3 degrees above zero. On average, Slany has 17 cloudy, 6 rainy, 5 partly cloudy, and 3 sunny days in December. The rains are usually light. December as well as January, February, and May is considered the most uncomfortable time to visit Slany.