Planning for the weather is a good way to make your trip to Idrija relaxing and enjoyable, especially when you’re splurging. The hottest months are usually July and August, with an average temperature of 18°C, while the coldest months are January and February, with an average of 2°C. The rainiest months in Idrija are September, November, May and July, with each month seeing an average of 191 mm of rainfall.