Here in the Bay Area we're used to fog.
Summertime tends to be the foggiest time along the coast — just ask those freezing tourists at Fisherman's Wharf in July.
Put simply, our summer marine layer happens when inland valleys heat up, drawing cool condensed moisture (fog) from over the Pacific Ocean inland through the Golden Gate and other gaps in the coastal hills.
But there's more than one way to freeze in the fog.
Winter is the time for tule fog, a low radiation fog that forms from the ground up and is named after the tule reeds in the marshes of the Central Valley.
Every so often in winter we see dense tule fog drift west, as far as the Golden Gate.