Taking into account the local weather in Cultus Lake is an important factor for planning your visit, especially if you plan to spend your trip poolside. 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.