What exactly is the Chehalis Gap, and how does it affect the weather?
The Chehalis gap is a low spot in the terrain along the Chehalis river, which runs to the south of the Olympic mountains and the various mountains to the south, including the Willapa Hills. That gap funnels moist air inland, often leading to a rapid transition from clear skies to low clouds overnight. When winds blow through the Gap (the Chehalis Gap, not the clothing store), the winds accelerate. Westerly winds result in gusty winds to the east of the Gap, while easterly winds result in gusty winds to the west of the Gap...often double the speed of winds elsewhere.