According to the National Weather Service, the upcoming Santa Ana event is likely to involve a record-setting difference in air pressure for this time of year between coastal California and areas well inland. It’s these air pressure differences that are the engine that drives the Santa Ana winds.
Given that many Santa Ana wind events have occurred throughout history in late October and early November, the likelihood of a record-strong pressure gradient is especially concerning. In general, the greater the difference in air pressure over short distances, the stronger the winds will blow.
The ominous forecast details for Southern California
As of early Tuesday afternoon, the Weather Service forecast office in Los Angeles was predicting winds to reach as high as 70 mph in valley locations between Tuesday night and Thursday morning, with the peak risk coming early Wednesday morning into the afternoon. At higher elevations, winds could reach or exceed 80 mph, the agency said.
The cool, downsloping winds rushing in from the Great Basin region will compress the air as they descend from higher terrain, causing the air mass to become bone dry. Relative humidity levels in Southern California during the upcoming event are likely to be between 3 and 10 percent, though in some places they could get down to just 1 to 2 percent, the Weather Service predicts.
Even without any wildfires to worry about, such winds could topple trees and power lines and lead to coastal flooding on Catalina Island. In an online forecast discussion, the NWS called the upcoming event “a high-end and dangerous event.”
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