Numerical modeling of the Santa Barbara Sundowner of 27 June, 1990

The south slopes of the Santa Ynez mountains experience mild to strong downslope winds 3-4 times per year (Ryan 1996). Known locally as Sundowners, these winds have occasionally reached severe levels. During strong to severe Sundowners, the main danger is not from the wind, but from fire advancing downslope towards the city of Santa Barbara and the surrounding communities. This paper investigates the mechanisms of Sundowner winds with the Pennsylvania State University/National Center for Atmospheric Research (PSU/NCAR) mesoscale meteorological model, version 5 (MM5) and compares the results to severe downslope wind theory. The severe Sundowner of June 27th, 1990, which pushed an arson-ignited fire that destroyed over 500 structures into the city, is used as a case study. The results indicate that the surface cooling of the south facing slopes of the Santa Ynez mountains can act as the trigger mechanism for the Sundowner winds in the late evening.