In December, the weather in Rapid City is typically cold. Average daily high temperature in December is about 2 degrees above zero. On average, Rapid City has 14 sunny, 9 partly cloudy, 4 cloudy, 3 snowy, and 1 rainy day in December. The snowfalls are usually light. December as well as January, February, March, and April is considered the most uncomfortable time to visit Rapid City.