369 Predictability of Sundowners—A Downslope Windstorm near Santa Barbara, California

Monday, 8 January 2018
Exhibit Hall 3 (ACC) (Austin, Texas)
Craig M. Smith, DRI, Reno, NV; and B. J. Hatchett and M. L. Kaplan

Sundowners are a downslope windstorm that occur over the Southern slopes of the Santa Ynez range along the Central California coast that have resulted in 25+oF early evening temperature ramps in Santa Barbara. Historically, most extreme fire events in the area, including the Whittier Fire, Sherpa Fire, Painted Cave, Montecito Tea, Jesusita and Sherpa fires, have occurred contemporaneously with Sundowner meteorological conditions. The dynamics of Sundowners are controlled by the interactions of the coastal offshore jet, sea breeze in the Santa Ynez valley, and intrusions of the lee slope jet into the marine boundary south of the mountain range. In this study we quantify the predictability of Sundowners using a high resolution operational forecast model with particular emphasis to a systematic bias towards the over-prediction of these downslope windstorms events, including the prevalence of false alarms and explore possibilities for a bias correction of those deficiencies using limited surface data for validation.
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