April in Great Falls is the rainiest month of the year. In April, the weather in Great Falls is typically warm. Average daily high temperature in April is about 11 degrees above zero. On average, Great Falls has 11 rainy, 11 partly cloudy, 7 sunny, and 1 cloudy day in April. The rains are usually moderate. April as well as January, February, March, and May is considered the most uncomfortable time to visit Great Falls.