Karl the Fog
San Francisco's Famous Fog Patterns
Marine Layer
SF's iconic fog forms when cool Pacific Ocean air meets California's warm interior valleys, creating a marine layer that blankets the city.
Fogust
July and August bring peak fog season, when tourists arrive expecting summer sunshine but find Karl instead. It's SF's coldest summer months!
Microclimates
The Sunset and Richmond districts can be 15°F cooler and completely fogged in while the Mission basks in sunshine. Twin Peaks blocks the marine layer.
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