A 400-mile stretch of dense Tule fog has blanketed California’s Central Valley and stretched into the Bay Area, according to the National Weather Service.
The fog — a winter hallmark of the San Joaquin and Sacramento valleys — has re-formed nightly for more than a week, reducing visibility along Interstate 5, Highway 99 and several connecting routes. Dense fog advisories remain in effect across the San Joaquin Valley, where the weather service’s Hanford office warned of “high transportation risk.”
Named for the Tule reeds that grow in the region’s wetlands, Tule fog is a type of radiation fog, unrelated to nuclear radiation, that develops when a “cool, moist layer of air from the Pacific close to the surface, clear skies above and light winds” combine to produce exceptionally dense fog in the Central Valley from late October through February. It is most persistent in sheltered valleys where wind cannot disperse it…