Weather will likely play an important role when you plan your trip to Great Falls, but bear in mind that cheaper options are usually available when the weather isn't as good. The hottest months are usually July and August, with an average temperature of 19°C, while the coldest months are February and December, with an average of -3°C. The snowiest months in Great Falls are April, February, October and March, with each month seeing an average of 37 cm of snowfall.