When you think of “windy” places, Southern California (SoCal) likely doesn’t come to mind. But SoCal happens to be home to one of the most extreme local wind events in the United States—the Santa Ana Winds.
California…Where the winds come sweeping down
The Santa Ana winds are warm, dry winds that blow during the cool season months (October to March). They form when high pressure builds over the Great Basin—the geographic area bound by the Rocky Mountains to the east and the Sierra Nevada to the west—and when low pressure sits over the California coast.
As is true of any wind, it’s this neighboring difference in pressure that makes the Santa Anas blow.
As air moves from the Great Basin westward toward California, where pressure is lower (air flows from high to low pressure), it gains speed as it whips through mountain valleys and passes.
The resulting airflow can reach speeds upwards of 30 mph, and gusts of more than twice this speed. The windstorms can last for several days on end.
Not only are Santa Ana winds swift, but they’re often hot and dry. As the air descends downslope from the Great Basin’s high elevation terrain to the low-lying coast, it compresses, which causes it to warm by tens of degrees Fahrenheit per mile it travels.
This compression also causes the air’s humidity to plummet. It isn’t uncommon for air associated with the Santa Anas to have humidity values in the single digits (anything under 10% is considered bone dry).
(Similar weather events occur in the U.S. Rockies, where they’re called chinooks, and in Norway, where they’re known as foehn winds.)
In January 1847, U.S. Commodore Robert Stockton described the fierce Santa Ana winds while camped near Santa Ana Canyon: “The wind blew a hurricane (something unusual in this part of California), and the atmosphere was filled with particles of fine dust, so that one could not see, and but with difficulty breathe.”
One of the strongest Santa Ana events in weather history occurred in December 2011. During this event, locations in the San Gabriel Valley, including Pasadena, CA, were pommeled by 97 mph windspeeds and gusts of up to 167 mph!
Why ‘Santa Ana’?
No one knows for sure why the winds take the nickname “Santa Ana.” Some stories say the name originates from Satanas—an archaic Spanish word for “devil” which was given to the winds because of their devilish weather conditions.
Others insist the name comes from the feast day of Santa Ana or Saint Anne (Mary’s mother); but this likely isn’t true since this feast day occurs outside of Santa Ana season, on July 26th. Still others claim the winds are named for the 19th century Mexican General Antonio López de Santa Anna, whose cavalry stirred up clouds of dust during military campaigns.
However, most agree the name likely refers to the Santa Ana Canyon and/or Santa Ana Mountains which are both located in SoCal.
It is also said that the seasonal winds tend to make residents feel “edgy” and exhibit crazy behavior, much like that linked to full moons.
Fanning Wildfires in the West
While the origins of the “Santa Ana” name may be the stuff of legend, the damage these winds cause is very real. The extreme winds can topple trees and power lines, and the dust carried from nearby deserts can even wreak havoc on residents’ allergies.
But more importantly, the heat, dryness, and strong winds can exacerbate fire weather conditions during peak wildfire season in the western United States.
During a late October 2019 Santa Ana event, meteorologists forecast wind gusts of 80 mph for locations across the SoCal region. The severity of the forecast led National Weather Service forecasters to issue an “extreme” red flag warning for the first time ever.
The office explained that, unlike an ordinary red flag warning, an extreme red flag warning meant weather conditions were “as dangerous for fire growth and behavior as NWS has seen in recent memory.”