5.4    Downslope Windstorms of San Diego County: Sensitivity to Resolution and Model Physics

Fovell, Robert, University of California, Los Angeles

Southern California's Santa Ana winds are a dry, sometimes hot, offshore flow that appears through the winter half-year.  They are particularly infamous for starting and fanning wildfires, especially in the autumn before the winter rains have started. The mountain gap nature of the Santa Ana flow pattern is widely recognized.  The winds push through passes and canyons that punctuate the local terrain, establishing several promiment "wind corridors" across the Los Angeles basin.

Less well-appreciated is the fact that the Santa Anas are also full-fledged downslope windstorms of the Boulder variety, especially in San Diego county, in which the topography lacks sizable gaps.  During October 2007, extremely strong winds progressed down the west-facing slope of the Laguna Mountains, sparking and spreading several blazes, including the incident named for Witch Creek that developed into the largest wildfire since 1889.

Simulation of the October 2007 event with WRF-ARW has revealed issues with the model (including resolution, initialization and model physics) as well as with the observations available for validation.  Recommendations for optimal simulation of these events will be made and the need for better and more complete observations will be demonstrated.