Fog along the West Coast of the United States has been documented as far back as the arrival of the Spaniards in the 16th century. Ship captains in later years learned to take it seriously; 100 years ago when the Marine Exchange in San Francisco was asked what proportion of coastal shipwrecks were the result of fog, the reply was “All of them.” Even today, aircraft pilots at coastal airports find themselves trying to stay on the right side of a very delicate balance between clear blue skies and zero-visibility IFR.
West Coast Fog Monster
Key Takeaways:
- Coastal fog is a frequent and historically significant phenomenon along the U.S. West Coast, peaking in summer and posing consistent challenges for aviation due to low visibility.
- It forms when moist oceanic air cools over cold, upwelled coastal waters, often intensified by high-pressure systems and confined within a shallow marine atmospheric boundary layer.
- Forecasting the precise onset, intensity, and inland extent of coastal fog is difficult due to its small-scale variability, limitations in observation tools, and dynamic nature.
- Pilots need to be aware of its unique characteristics, utilize specific data sources like visible satellite imagery and offshore dewpoint reports, and prepare for potential alternates or climbing above the typically shallow fog layer.
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