If you’re hoping to get lost in the rain on your romantic getaway, check out these details about year-round temperatures in Lerum: The hottest months are usually July and August with an average temp of 60°F, while the coldest months are February and January with an average of 33°F. The snowiest months in Lerum are January, December, February, and November, with each month seeing an average of 10 inches of snowfall.