The temperature reached 97 degrees in Downtown Los Angeles on Tuesday afternoon, and the unseasonably warm temperatures combined with low humidity levels and the arrival of Santa Ana winds are bringing a heightened risk of wildfires to parts of Southern California just west and north of Downtown Los Angeles this week.
The National Weather Service office issued a red flag warning, the highest level of fire alert, through 6 p.m. Wednesday for two separate pockets: One is spread between Los Angeles and Ventura Counties from the western San Gabriel Mountains into the Santa Susana Mountains. The other falls within the valleys of southeastern Ventura County and includes the cities of Thousand Oaks and Simi Valley.
The wildfire risk this year was significantly reduced in most of Southern California by early fall rains, but this region did not receive enough rain to fully end the threat. “The heavier brush is still dry, and that’s conducive to fire spread,” said Kristen Stewart, a fire weather meteorologist with the U.S. Forest Service.
Several other areas of Southern California, between San Diego and San Luis Obispo Counties, were under advisories for heat and wind on Tuesday, and many of these alerts are likely to continue into Wednesday.
Downtown Los Angeles was expected to reach only 92 degrees on Tuesday but the temperature kept rising, surpassing the previous daily record of 94 degrees set in 2008.
Santa Ana winds, also known as offshore winds, blow dry air from inland areas toward the coast, pulling moisture from trees and brush and making them more flammable. Imagine a large blow dryer over interior desert valleys that is pointed toward the coast when it’s turned on. Santa Ana winds are most common in the colder months, and this is their first appearance of the season, which runs fall through spring.
When catastrophic fires ignited in Los Angeles County in January, the flames were spread by Santa Ana winds blowing as fast as 100 miles per hour.
On Tuesday, morning sustained winds reached 30 m.p.h. and isolated gusts topped 45 m.p.h. in wind-prone areas. The winds had eased by late Tuesday afternoon but were expected to pick up again late Tuesday and continue into Wednesday morning.
Ms. Stewart said the fire risk was significantly higher in January because the exceptionally strong winds hit at a time when the landscape was especially dry — the region did not see any rain in the fall and through the early part of winter last year.
“Our fire indices were very, very high in January, but this time they’re below average because of the recent rain,” Ms. Stewart said. “But, of course, it doesn’t mean there’s no risk since it’s still going to be dry and breezy out there, and hot.”
One factor signaling fire risk this week is the humidity levels, which are predicted to fall to 8 to 15 percent on Tuesday and down to 5 to 10 percent on Wednesday. Low humidity means the atmosphere is generally more dry, and more conducive to fires.
What’s more, temperatures across Southern California are unseasonably high with Downtown Los Angeles beating its pervious sa expected to be unseasonably high oagain on TWednesday, about 10 to 15 degrees above normal in many locations.
Amy Graff is a Times reporter covering weather, wildfires and earthquakes.
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