How fog built the Bay Area

"Fog is a quintessential part of the Bay Area, a seemingly simple suspension of water in air that has shaped our culture and ecology since time immemorial. For us, it is the ghostly embodiment of cold weather and maybe our only chance at a white Christmas. At its core, it only needs two ingredients cool temperatures and humid air and it forms when moisture condenses to form a cloud close to the surface of the Earth."

"As winds blow in over the Pacific, they churn up the coastal ocean, bringing up frigid waters from the depths towards the surface. Paired with currents coming down from Alaska, this keeps the Bay Area waters in the crisp 50s throughout the year. Those same winds that cause the icy upwelling also bring in moist air, and as they hit the chilly ocean, the water in the air cools and condenses into fog."

Fog forms when moisture condenses near the Earth's surface, requiring cool temperatures and humid air. Coastal upwelling and Pacific winds bring frigid deep waters to the surface, while currents from Alaska help keep Bay Area ocean temperatures in the low 50s. Those winds carry moist air that cools over the chilly ocean and condenses into fog. In winter the fog usually stays near shore; in summer sea-breeze patterns draw it inland across the Peninsula and occasionally into the East Bay, producing the region's windy, foggy summers. Fog influences Bay Area ecology and human life and attracts scientific study. No known indigenous cultural expressions specifically related to fog survive for the Bay Area's first peoples.

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