Tule fog 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 late autumn and winter (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. Accidents caused by the tule fog are the leading cause of weather-related casualties in California.
If you’re going to ride in tule fog, you definitely need better than average bike lights. This morning we had a mild case; when it gets especially bad, I stay off the roads. (Yes, that oncoming train in the lower left of the photo is my bicycle.)