A low-pressure system parked over the Great Basin and Rocky Mountains created an extreme difference in pressure between the Mountain West and California late Sunday into Monday morning, pushing chilly, bone-dry air into the Golden State and kicking up powerful offshore winds.
Fierce gusts knocked mountaintops, tore through valleys and made their way all the way to the coast Monday morning amid what has been called the most severe wind event in California this year. Humidity levels dropped into the single digits and teens, and when combined with the blustery conditions, created extremely critical wildfire conditions with multiple small blazes sparking overnight.
Incredible wind speeds were recorded in the Bay Area, including a 58 mph wind at the Oakland Airport, a 72 mph gust on Mount Diablo near Blackhawk and an 89 mph wind on Mount St. Helena, 5.8 miles south of Middletown.
The Tahoe Basin saw some of the highest wind speeds, and the National Weather Service confirmed an official 94 mph reading at a gauge on a peak in Alpine Meadows.
Speeds over 100 mph were recorded on exposed ridgetops at several ski resort anemometers that aren’t monitored by the weather service for accuracy including a measurement of 102 at Mammath Mountain, 119 mph at a different Alpine Meadows location and 140 mph at the top of Chair 6 (elev. 9,186 feet) at Kirkwood Mountain Resort.
The 140 mph wind was recorded on a sensor that’s placed in the saddle of a highly exposed mountain, said weather service forecaster Tony Fuentes. Last year, the gauge measured a very questionable reading over 200 mph.
“It’s possible the location saw a 140 mph wind this morning,” said Fuentes. “It’s right on a ridgetop in a saddle there, so it can get more of a localized bump in the winds. It could be a really localized thing. There’s no way to verify it or throw it out.”
Scott Rowe, a forecaster with the weather service’s Sacramento office, concurred and said it’s hard to say whether this morning’s 140 mph gust came from a real reading or faulty equipment. “It’s as exposed as you can possibly imagine up there,” Rowe said.
In Southern California, the weather service measured a 96 mph gust in the San Gabriel Mountains just south of Santa Clarita.
Offshore winds aren’t uncommon in California in the fall, but this event was deemed especially severe, with the gusts not confined to higher elevations and blowing into valleys. There were reports of fallen trees, branches and power lines across the region. PG&E preemptively cut power to tens of thousands of customers across the state to reduce the risk of fires sparking from fallen equipment.
While the strong winds are expected to dissipate by midday Monday, another series of strong winds, sustained 25 to 40 mph winds in the mountains and along ridges with gusts of up to 70 mph, is expected to hit Northern California’s higher elevations by Monday night.
“We may be past the peak of the winds, but we’re still experiencing very strong gusts,” Cal Fire spokesperson Daniel Berlant told KCBS on Monday morning.
The winds ushered in an extremely dry air mass, and humidity levels dropped to remarkably low levels. Half Moon Bay’s relative humidity dropped from 94% to 12% in 2 hours Sunday night as the offshore flow pushed to the coastline, according to the weather service. To the north, the city of Redding recorded a humidity level of 5%. In the Sierra, levels ranged from 3-15% overnight.
“It’s as dry as it can possibly be — desert dry and sometimes even drier,” said Rowe. “This air mass is originating from the Great Basin, bringing that dry air with it.”
Multiple fires sparked across the Bay Area overnight — including blazes in Castro Valley, Sebastopol and Healdsburg — and these were all quickly contained. “Lots of small fires started but we were able to contain them,” said Berlant.
To the north, a blaze called the Olinda Fire started early Monday south of Anderson in Shasta County but reached only 5 acres before being 100% contained. Nearby, the Dersch Fire started east of Anderson in Shasta County and was 133 acres and 90% contained as of 7:30 a.m. Monday.
The Point Fire ignited east of Forest Hill in Placer County and was 20 acres as of 8:30 a.m. Monday morning, with aircraft overhead dropping fire retardant.
Author: Amy Graff