Weather will likely play an important role when you plan your trip to Thonon-les-Bains, 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 18°C, while the coldest months are January and February, with an average of 4°C. Average annual precipitation for Thonon-les-Bains is 1421 mm.