Dangerous Diablo winds fueling Kincade fire with wind gusts up to 76 mph

Forecasters had been warning for days that dangerous Diablo winds were coming. Now, those conditions have produced a monster fire in Sonoma County.

The Kincade fire was burning out of control, consuming 10,000 acres in just a few hours.

What are the conditions firefighters are facing?

The area around the fire is seeing severe fire weather with sustained winds of roughly 50 mph and gusts as high as 76 mph, said National Weather Service meteorologist Matt Mehle. Temperatures around midnight were about 70 degrees, and humidity levels were about 10% to 15%.

Wind speeds in some of the valleys around the fire were lower, around 25 mph.

Mehle said that based on cameras and satellite data past midnight, he was continuing to see what firefighters call rapid rates of spread that can contribute to potentially extreme fire behavior. Based on his observations, the overall footprint of the fire was moving from the northeast to the southeast.

The Bay Area is in a classic Diablo wind situation, a common weather phenomenon for this time of year that sends extreme gusts from the northeast to the southwest. Such winds have had a long history in California of rapidly spreading fire.

The winds are expected to subside later Thursday, Mehle said. But humidity levels will continue to worsen, dropping into the single digits, and temperatures will rise to as high as 90 degrees in the fire area.

What is the larger picture in California?

Strong winds and extremely dry conditions will result in widespread critical fire weather conditions throughout California on Thursday, according to the National Weather Service. Strong surface high pressure in the Great Basin will promote strong northeasterly Santa Ana winds.

Southern California population centers listed at critical risk include Santa Ana, Anaheim, Riverside, San Bernardino and Oxnard. Population centers at extreme risk include Ontario, Fontana, Santa Clarita, Rancho Cucamonga and Pomona.

How about the weekend?

The National Weather Service in Sacramento is forecasting another wind event starting late Saturday that could be the strongest so far this fall.

“Downed trees, power outages & difficult driving conditions are possible,” the weather service said Wednesday in a tweet.

What about the power situation?

More than half a million utility customers could lose power this week in California.

Southern California Edison said more than 308,000 customers in seven counties — Ventura, Los Angeles, San Bernardino, Riverside, Orange, Kern and Santa Barbara — could face blackouts starting Wednesday night and rolling into midday Thursday.

Pacific Gas & Electric Co. on Wednesday shut off power to customers in the Sierra Nevada foothills about 2 p.m. An hour later, counties in the north San Francisco Bay Area began to lose service. By 1 a.m. Thursday, portions of San Mateo and Kern counties were also expected to be in the dark. In total, 179,000 customers are expected to have their power cut.

What are Diablo winds, and how are they different from the normal weather pattern for the Bay Area?

The normal weather pattern near the coast is for moist sea breezes to come off the Pacific Ocean and into the land. But in the fall, high pressure that builds into the Great Basin in Nevada and Utah causes wind to shift in the opposite direction, according to Jan Null, adjunct professor of meteorology at San Jose State University and former meteorologist with the National Weather Service.

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In the Bay Area, they’re called Diablo winds; in much of Southern California, they’re called Santa Ana winds. A similar wind that threatens Santa Barbara are called sundowner winds. In the Sacramento Valley area, Jarbo Gap winds are what locals call the gusts that howl through the Feather River Canyon as high-pressure air over Nevada and Utah seeks a path through the state’s mightiest mountain range, the Sierra Nevada, to fill the lower-pressure voids on the California coast.

In Northern California, the winds arrive when air coming down from Nevada and Utah, falling from an elevation of about 4,000 feet, gets pushed down to sea level. That air is compressed, and warm winds are created.

What are examples of how Diablo and Santa Ana winds have fueled fast-moving wildfires?

A classic example of a destructive fire fueled by Diablo winds is the October 1991 firestorm that struck the Oakland and Berkeley hills, killing 25 people and destroying about 2,900 structures. Until 2017, that fire was the most destructive in California history.

More fire coverage

Two more fires have been more destructive since then. The Tubbs fire of Sonoma and Napa counties in October 2017 roared 12 miles in four hours into Santa Rosa, killing 22 people and eventually destroying more than 5,000 structures.

The Camp fire of Butte County, which destroyed much of the town of Paradise and destroyed more than 18,000 structures last November, is now the state’s most destructive fire on record. A Los Angeles Times analysis published last year said the fire grew at a rapid clip — about 4,600 acres an hour — a rate that was matched by the Tubbs fire and other California fires. The Camp fire led to more than 80 deaths, the deadliest in California’s modern record.

California’s fourth most destructive fire, the Cedar fire of San Diego in 2003, grew even faster than the Camp fire. That fire had kindled for hours until a Santa Ana wind rolled in at midnight. By 3 a.m., the wind-driven fire had jumped a river and a reservoir and run nearly 17 miles. In the three-hour run, the fire spread an average of more than 19,600 acres an hour. Fifteen people were killed and more than 2,800 structures destroyed.

The same high-pressure, low-pressure gradient last year set up a Santa Ana wind event that pushed the Woolsey fire into Malibu. Its pace in the first three hours was 21,290 acres an hour. It destroyed more than 1,600 structures and caused three deaths.

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