Tule fog

Tule fog /ˈtuːliː/ is a thick ground fog that settles in the San Joaquin Valley and Sacramento Valley areas of California's Great Central Valley. Tule fog forms from late fall through early spring (California's rainy season) after the first significant rainfall. The official time frame for tule fog to form is from November 1 to March 31. This phenomenon is named after the tule grass wetlands (tulares) of the Central Valley. Tule fog is the leading cause of weather-related accidents in California.