Red-flag warnings for elevated fire weather risks are in effect for six states, including parts of California.
Typically, Santa Ana wind events, which feature winds blowing from northeast to southwest across the L.A. Basin, reach a peak frequency during late fall. Such winds have been associated with infamous wildfires in this area because they bring sinking, warming and drying air and can power fast-moving blazes.
From Monday through Tuesday night, a surface high-pressure area settling into the Great Basin is powering offshore winds across Southern California.
According to the National Weather Service, the difference in pressure over a small region that drives wind or gradient is at an “almost unprecedented” level for June, demonstrating how unusual this Santa Ana event is.
“This is indeed a very unusual event, almost unprecedented in terms of the offshore flow,” the NWS Los Angeles office stated in an online forecast discussion Monday.
A high-wind warning is in effect for the mountains of Ventura and Los Angeles counties through 4 p.m. Eastern time Monday. “Damaging winds will blow down large objects such as trees and power lines. Power outages are expected,” the NWS warned.
In recent years, deadly fires have been traced to the interaction between power lines and high winds, including the tragic fire in Paradise, Calif., in 2018, which was the state’s deadliest on record. But the conditions conducive to them have usually occurred in the fall.
“Santa Ana conditions are not unheard of in Southern California in June, but they are rare,” said Evan Bentley, a fire weather forecaster at the Storm Prediction Center. “However, when they do occur, it is particularly concerning because vegetation is usually in the process of drying out and the inland deserts are very dry, which leads to extremely dry air when offshore flow occurs.” Relative humidity levels of just 5 to 15 percent are occurring on Monday, according to the NWS.
The NWS Los Angeles forecast office warns of the “potential for rapid fire growth and extreme fire behavior” if any blazes do get going. The red-flag warning issued for Los Angeles on Sunday is the first of 2020.
The winds, which heat up and dry out as they move toward the coast, will also bring oppressive heat to coastal Southern California this week. Heat advisories are in effect from San Diego northward into metro Los Angeles, for temperatures in the mid-90s.
On Tuesday, San Diego may hit 90 degrees for the first time this year, while Los Angeles could break its daily record of 94 degrees.
The widespread dangerous fire weather blanketing the southwestern United States began this weekend, sparking several fires in Southern California, Arizona and other areas. These conditions were related to a dip, or trough, in the jet stream that set up across the West.
On Sunday night, wind gusts above 60 mph were observed in the Santa Monica mountains, and a gust to 52 mph occurred at Santa Monica Pier on Monday morning, according to the NWS.
Farther east, a different atmospheric setup is bringing strong, dry winds to New Mexico and southeast Colorado. Smoke plumes from fires were observed in these areas Sunday afternoon, according to the NWS’s Storm Prediction Center.
The Storm Prediction Center designated a vast area of “elevated” to “critical” fire weather and an “extremely critical” swath in eastern Colorado on Sunday, an area in extreme drought. Varying degrees of drought across the West, combined with repeated heat waves in spring 2020, point to a quickly drying landscape that makes the effects of these early-summer winds all the more potent.
Fires near the San Francisco Bay area
The danger in Southern California isn’t the only recent fire threat in the state.
On Saturday afternoon, the Quail Fire ignited near Vacaville, about halfway between San Francisco and Sacramento. The blaze spread quickly, prompting evacuation orders and destroying three structures, while threatening 100 more. By Saturday night, it had grown to 1,400 acres and currently stands at 1,837 acres and 50 percent containment, with all evacuation orders lifted.
Given the threat of the existing fire, along with a shift to northerly winds and low humidity, the Sacramento NWS office issued a red-flag warning for the area on Sunday, effective through 8 p.m. Monday.
Weather records for Vacaville show that only a trace of rain has fallen there in the past two months, so not all areas have seen rainfall during occasional cool and wet interludes in Northern California. Heat waves have also scorched the region this spring.
“We shouldn’t be seeing this until July,” said James Mathews, a meteorologist with the National Weather Service in Sacramento.
“We are at least a month ahead of schedule here,” he said, referring to the dryness of the vegetation.