Where Is Heavy Fog Most Prevalent in the Continental U.S.? The Northern West Coast

The Northern West Coast—coastal Northern California, Oregon, and Washington—is one of the foggiest regions on Earth.

Why Here?

• Cold Ocean Currents: California Current chills surface water.
• Warm Land Temperatures: Especially in summer, inland heating creates strong temperature contrast.
• Onshore Winds: Prevailing westerlies push moist marine air over cold water, then onto land.

This combination produces persistent advection fog (marine layer) that blankets coasts and inland valleys, particularly June–September. The Great Plains, High Desert, and Southern Plains experience fog far less frequently.