If you’re looking forward to lots of outings with your partner, check out these details about year-round temperatures in Dehradun: The hottest months are usually May and June with an average temp of 80°F, while the coldest months are January and December with an average of 56°F. The rainiest months in Dehradun are July, August, September, and June, with each month seeing an average of 13 inches of rainfall.