If you’re looking forward to lots of outings with your partner, check out these details about year-round temperatures in Cultus Lake: The hottest months are usually July and August with an average temp of 61°F, while the coldest months are February and December with an average of 35°F. The rainiest months in Cultus Lake are November, January, December, and March, with each month seeing an average of 12 inches of rainfall.