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.