Yesterday's violent wind gusts which tore through much of Los Angeles county were influenced by local topography including mountains, canyons and passes—as much as by the weather elements which created them.
Strong Santana winds are a regular late fall visitor to the L.A. and greater Southern California region. While Thursday's event was entirely predictable, the presence of transverse mountain ranges in the Southland are a precursor to an often wildly unpredictable set of circumstances accompanying each and every episode of Santana winds. Differing elevations, canyons and passes make predicting wind intensity and location an art, and a very challenging one. Typically, the strongest gusts usually tend to be more localized, particularly affecting Newhall Pass (Interstate 5 corridor from L.A. to Bakersfield) and Cajon Pass which divides the San Gabriel mountains from the San Bernardino mountains, home to Interstate 15.
Under the right circumstances, other parts of Los Angeles, including west L.A., the San Gabriel valley and areas which are often sheltered from these winds are blasted-- owing to differing elevations in the nearby San Gabriel mountains. Pasadena and nearby areas were particularly hard hit Thursday because air movement was powerful at all levels in the atmosphere. Strong winds from the north easily slipped over the relatively moderate elevations immediately north of the Arcadia - Pasadena area. The west to east orientation of the San Gabriel mountains often accounts for a “wind shadow” effect, typically blocking strong northerly winds from strongly surfacing in these areas. But Thursday's winds packed enough impetus to easily cross the 5,000 to 6,500 ft. summits immediately north of Pasadena. Stronger than usual surface pressure difference caused Thursday's winds to "bottom out" across the San Garbriel and Pomona Valleys. Claremont, which is rarely affected by strong northerly winds was blasted with 50-60 mph. gusts. Claremont lies in the wind shadow of nearby Mt. Baldy, the highest ;point the San Gabriel mountains. Mt. Baldy tends to block strong north winds, with its 10,080 ft. summit.
Strong northerly winds often tend to remain aloft, touching down in localized areas near passes and canyons.
Air, much like water seeks the path of least resistance. Lower altitudes, narrow and canyons passes can enhance and funnel the movement of air in their vicinities .
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