Development of an objective methodology for diagnosing Santa Ana winds

Santa Ana winds are strong offshore winds that occur across southern California composing a critical fire weather pattern into autumn prior to the onset of the rainy season. Although Santa Ana winds express localized features associated with the confluence of adiabatically compressed flow and topography, they are often characterized by distinct synoptic-scale features that forecasters use in subjective pattern recognition to predict their occurrence. This study employs two key synoptic-scale factors responsible in fostering the occurrence of Santa Ana winds, mean sea-level pressure gradient and 850-hPa cold air advection using, using 6-hourly NCEP-NCAR reanalysis, validated using in-situ observations from 51 Remote Automated Weather Station (RAWS). Our results demonstrate that these coarse scale predictors effectively capture the surface signature of Santa Ana conditions. This methodology provides a simple and effective means of developing both an extended record of historical Santa Ana event occurrence, as well as a methodology that could be easily employed in real time to provide mid-range (6-14 day) forecasts of Santa Ana events.