Weather forecasts and warnings are the most important services provided by the meteorological profession. The effective development of forecasting methods rests upon comprehensive knowledge of the phenomena to be forecast. To help provide such knowledge, this review includes a chronological summary of pertinent information concerning fog on the U.S. west coast. There is increasing evidence that periods of dense fog at National Weather Service west coast stations fall within a 5- to 15-day sequence of synoptic events. Further, such sequences may be divided into four distinct phases: initial conditions, fog formation, fog development and extension, and stratus. A separate article will review West Coast fog forecasting approaches and present resulting methods.