The Santa Ana Winds are scouring Southern California once again and destructive wildfires have reignited. These hot, dry, powerful winds typically occur during the fall and winter months, as periods of high pressure develop across the Great Basin. Like a giant piston, this high pressure zone creates sinking air over the high deserts of the Basin; in concert, winds flow clockwise around the center of this pressurized air mass and are directed into the mountain ranges of Southern California. Much of this flow is forced to rise over the mountains while some is funneled through the major passes (especially Cajon Pass, between the San Gabriel and San Bernardino Mountains).
As the pressured air descends from the high desert and mountains into the Los Angeles Basin, it compresses, dries out and heats up, often bringing the highest temperatures of the year to the coastal cities. The speed of the wind is augmented in canyons of the Transverse and Peninsular Ranges, sometimes reaching 100 mph or more; while the power of these winds is destructive in itself, the winds also fan the flames of any wildfires that develop, making efforts to control them nearly impossible.
Once the high pressure in the Great Basin moves on to the east, the winds subside and "onshore westerlies" bring cooler, more humid air in from the ocean. Of course, Southern California residents hope that this marine flow will also bring rain to the valleys and foothills, nourishing and restoring the vegetation before the next round of Santa Ana winds.
As the pressured air descends from the high desert and mountains into the Los Angeles Basin, it compresses, dries out and heats up, often bringing the highest temperatures of the year to the coastal cities. The speed of the wind is augmented in canyons of the Transverse and Peninsular Ranges, sometimes reaching 100 mph or more; while the power of these winds is destructive in itself, the winds also fan the flames of any wildfires that develop, making efforts to control them nearly impossible.
Once the high pressure in the Great Basin moves on to the east, the winds subside and "onshore westerlies" bring cooler, more humid air in from the ocean. Of course, Southern California residents hope that this marine flow will also bring rain to the valleys and foothills, nourishing and restoring the vegetation before the next round of Santa Ana winds.
