If you’re hoping to get lost in the rain on your romantic getaway, check out these details about year-round temperatures in Brunnen: The hottest months are usually July and August with an average temp of 59°F, while the coldest months are January and February with an average of 32°F. The rainiest months in Brunnen are August, July, June, and May, with each month seeing an average of 9 inches of rainfall.