In the San Juan Islands, some residents call August-'Fog-ust'. Why all the fog here in August?
Oddly enough, it's because we have fewer weather systems that produce thick clouds and rainfall. Since there's cooler water off the coast of Washington, the high pressure systems that take up long-term residence off the coast is able to drive that shallow layer of moist ocean air inland, where it cools and condenses into fog overnight. That's able to happen since skies above are mostly clear, allowing for rapid 'radiational' cooling.