SACRAMENTO - Combine a good soaking rain with light winds and clear skies and fog develops.
When visibility drops to or below 0.25 miles, the National Weather Service will issue a Dense Fog Advisory.
There are different types of fog, including radiation fog, advection fog, upslope fog, evaporation or mixing fog, ice and freezing fog.
Radiation fog is the most common in the Central Valley. The foggy months are between the end of fall and early spring during the rainy season.
Fog generally occurs after the significant first rainfall. Radiation fog develops closest to the ground. As the earth surface cools, there's enough moisture and humidity levels reach 100 percent, creating conditions for fog.
Radiation fog is also known as tule fog. The name comes from the tule grass wetlands in the valley. Tule fog can develop from Redding to Bakersfield.
The record for consecutive days of fog for Sacramento is 17. This happened Dec. 12-28, 1985.