Weather is probably a major factor when you plan your trip to Roussillon-en-Isere, but bear in mind that cheaper options are usually available when the weather isn't as good. The hottest months are usually August and July, with an average temperature of 19°C, while the coldest months are January and February, with an average of 4°C. Average annual precipitation for Roussillon-en-Isere is 1012 mm.