If you’re hoping to get lost in the rain on your romantic getaway, check out these details about year-round temperatures in Idrija: The hottest months are usually July and August with an average temp of 64°F, while the coldest months are January and February with an average of 36°F. The rainiest months in Idrija are September, November, May, and July, with each month seeing an average of 8 inches of rainfall.