January in Great Falls is the windiest and the cloudiest month of the year. In January, the weather in Great Falls is typically freezing. Average daily high temperature in January is about zero. On average, Great Falls has 12 cloudy, 10 partly cloudy, 6 sunny, and 3 rainy days in January. The rains are usually light. January as well as February, March, April, and May is considered the most uncomfortable time to visit Great Falls.