If you’re hoping to get lost in the rain on your romantic getaway, check out these details about year-round temperatures in Brush Prairie: The hottest months are usually August and July with an average temp of 64°F, while the coldest months are December and February with an average of 40°F. The rainiest months in Brush Prairie are December, November, January, and March, with each month seeing an average of 11 inches of rainfall.