Tule Fog in the Central Valley, December 12, 1997

GOES 9 Visibile Sat Image

Visible Sat Image Superimposed on Plot of Surface Weather Information

Plot of Weather Information for SF Bay Area

Great Basin High In the absence of the jet stream, thermal pressure systems dominate. During the winter, intense cooling in the Great Basin results in the formation of a thermal high pressure area there.  The high is associated with sinking air and clear skies.  As will be seen below, this produces the conditions favorable for the formation of radiation (also known as radiation or ground) fog. Tule Fog in the Central Valley clear, calm nocturnal conditions encourage radiational cooling air in contact with the ground is cooled by conduction this air becomes denser than the air around it and slides into hollows and valleys Central Valley is therefore the site of massive banks of tule fog