Extreme Fire Weather Associated with Nocturnal Drying in Elevated Coastal Terrain of California

Abstract The second largest fire shelter deployment in U.S. history occurred August 2003 during the Devil Fire, which was burning a remote and rugged region of San Francisco Bay Area, when relative humidity abruptly dropped middle night, causing rapid growth. Nocturnal drying events higher elevations along California’s central coast are unique phenomenon that poses great risk to wildland firefighters. Single-digit with dewpoints below −25°C is not uncommon summer nights this region. To provide management community knowledge these hazardous conditions, an event criterion established develop climatology nocturnal investigate synoptic patterns associated events. A lower-tropospheric source dry air found over northeastern Pacific Ocean corresponding area maximum low-level divergence subsidence. This forms above marine inversion advects inland overnight layer immerses higher-elevation terrain warm air. An average 15–20 per year occur greater than 700 m their characteristics highly variable, making them challenge forecast.