Planning for the weather is a good way to make your trip to Donnelly relaxing and enjoyable, especially when you’re splurging. The hottest months are usually July and August with an average temp of 61°F, while the coldest months are December and January with an average of 25°F. The snowiest months in Donnelly are February, January, March, and December, with each month seeing an average of 27 inches of snowfall.