Wildfires fuelled by “life-threatening” Santa Ana winds – warm, dry air formed in the Great Basin Desert of America’s southwest – are forcing the evacuation of over 100,000 residents in Southern California.
Image: Graphic News
Santa Ana winds are formed when a high pressure ridge forms over the the Great Basin and upper Mojave Desert which includes most of Nevada and Utah, in contrast to a low pressure area over the coast.
Unlike the typical airflow at this time of year, a “kabatic” wind is generated which flows downhill, over the mountains towards Los Angeles.
The hot dry air is funnelled through the mountain valleys and canyons of the Sierra Nevada, San Gabriel and San Bernardino Mountains where the greater pressure increases the temperature.
With a relative humidity of under 20%, and with typical wind speeds of 90km/h, gusting at up to 130km/h, the Santa Ana dries out vegetation so it burns more readily.