Terrain-Trapped Airflows and Orographic Rainfall along the Coast of Northern California. Part I: Kinematic Characterization Using a Wind Profiling Radar Monthly Weather Review

This study develops an objective method of identifying terrain-trapped airflows (TTAs) along the coast of Northern California and documenting their impact on orographic rainfall. TTAs are defined as relatively narrow air masses that consistently flow in close proximity and approximately parallel to an orographic barrier. A 13-winter-seasons dataset is employed, including observations from a 915-MHz wind profiling radar along the coast at Bodega Bay (BBY, 15 m MSL) and surface meteorology stations at BBY and in the coastal mountains at Cazadero (CZD, 478 m MSL). A subset of rainy hours exhibits a profile with enhanced vertical shear and an easterly wind maximum in the lowest 500 m MSL, roughly the same depth as the nearby coastal terrain. Both flow features have a connection to TTAs along the coast of Northern California.