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 during the winter and 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. Motor vehicle accidents caused by the tule fog are the leading cause of weather-related casualties in California.