If you’re hoping to get lost in the rain on your romantic getaway, take a look at these details about year-round temperatures in Flums: The hottest months are usually July and August, with an average temperature of 15°C, while the coldest months are January and February, with an average of -1°C. The rainiest months in Flums are August, June, July and May, with each month seeing an average of 235 mm of rainfall.