Every October in California, leaves and temperatures fall, pumpkins dot the fields and college football season takes stride.

But despite the trappings of autumn, October is California’s most dangerous month for wildfires, posing a deadly mixture of heavy seasonal winds, unpredictable weather patterns and bone dry vegetation.

If history is a guide, the Loma fire, which began burning through a remote corner of the Santa Cruz Mountains on Sept. 25, may not be the end of the Bay Area’s fire threats for the year. It may just be the beginning.

Five of the six most destructive wildfires in state history, ranked by the number of homes burned down, have occurred in October. Chief among them is the Oakland hills fire, which destroyed 2,843 homes and killed 25 people on a blustery day in 1991.

The largest fire in recorded state history, the Cedar fire, which charred 273,246 acres — an area 10 times the size of San Francisco — in San Diego County, started in October 2003. And so did California’s deadliest fire, the 1933 Griffith Park fire in Los Angeles, which killed 29 people.

“People think that we are getting out of fire season by October,” said Craig Clements, director of the Fire Weather Research Laboratory at San Jose State. “No. We are getting into it.”

Fire crews around the state look at October with a sense of foreboding.

“This is the time of year that we hold our breath and watch the weather closely,” said Daniel Berlant, a spokesman for the California Department for Forestry and Fire Protection, known as Cal Fire.

Experts say there are two reasons.

DRY MONTHS

The first is moisture. As any camper knows, wet wood doesn’t burn. California has a Mediterranean climate, with nearly all of the rain falling from November to April. By the time calendars turn to October, many places have gone six months without receiving an inch of precipitation.

That means the amount of water in shrubs, trees and grasses is often at the lowest level of the year by October. Fire scientists call it “fuel moisture level” and say it is the single largest determining factor for how primed an area is to burn.

“We get all our precipitation in the winter and hope it is enough to sustain us,” Clements said. “We don’t get any in the summer, so the fuels basically dry out. As we get into October, the shrubs are at critically low moisture levels.”

Clements and his students regularly sample fuel moisture levels of chamise, a common flowering shrub, near Los Gatos. Over the past 10 years, they have found those levels have peaked in April at 162 percent on average and steadily declined to 59 percent by mid-October, rising again as winter rains begin to fall. (Because the water in a plant can weigh more than the dry parts of the plant, moisture content can be greater than 100 percent. A green leaf, for example, may hold twice as much water as dry material, which would give it a moisture content of 200 percent.)

BLOWIN’ IN THE WIND

The second factor that makes October particularly perilous is wind. Because of seasonal weather patterns, strong winds blowing west from dry inland areas such as the Nevada desert bring hot, punishing air that can spread embers and flames at breathtaking speed. In Northern California, they are called Diablo Winds; in Southern California they’re called Santa Ana Winds.

They have garnered an ominous reputation in California culture, particularly the Southern California variety, which can exceed 50 mph.

In his 1946 story “Red Wind,” Raymond Chandler, the famed detective writer, described Santa Anas as “those hot dry winds that come down through the mountain passes and curl your hair and make your nerves jump and your skin itch. On nights like that every booze party ends in a fight. Meek little wives feel the edge of the carving knife and study their husbands’ necks. Anything can happen.”

The Witch fire, which began with sparking power lines in Witch Creek Canyon near the eastern San Diego County town of San Ysabel on Oct. 21, 2007, raged out of control for two weeks, closing freeways and causing the evacuation of Del Mar, Chula Vista, Poway and other communities. Driven by strong Santa Ana winds, it eventually burned 197,990 acres, destroying more than 1,100 homes.

Diablo winds drove super-heated air through northern Oakland and southern Berkeley on Oct. 20, 1991, spreading embers from a small grass fire through dense hillside neighborhoods.

ESCAPED FIRE

Susan Piper escaped in her car with her 4-year-old twin daughters and 9-year-old daughter. Her house burned down amid a hellish chaos.

“It was bumper-to-bumper traffic,” she said. “There was a whole row of eucalyptus trees exploding in fire. I had to lean away from the door because it was so hot. I was so focused on getting us out of there. Nothing else mattered. It was a scary time.”

Eventually, she and her family rebuilt, and she became an advocate for fire planning, particularly clearing brush and other preventative measures. Now, as the 25th anniversary nears, she said, October always puts long-time residents on edge.

“The newer people don’t feel it with the intensity of people who were there,” she said. “When it gets hot, dry and windy, I get very nervous. I think what am I going to take with me?”

Fire officials say it is vital in October for residents in fire-prone areas to clear brush 100 feet around their homes, remove leaves and pine needles from roofs and gutters, take wood piles away from the sides of homes and prepare evacuation plans for their families.

If rains come in November and December, the risk will decline. But until then, don’t get complacent, they urge.

“We have to pace ourselves,” said Cal Fire’s Berlant. “This is not the end of the season. It could be the worst part, worse than the rest of the season combined.”

Loma Fire 2016

Acres burned: 4,416 acres.

Started: 2:42 p.m. Sept. 26, 2016.

Containment: 66 percent.

Location: Loma Chiquita Road and Loma Prieta Road, Los Gatos.

Cause: Under investigation.

Structures destroyed: 12 residences, 16 others.

Structures threatened: 163.

Structures damaged: 1 residence.

Fire crews: 1,964.

Equipment: 119 engines, 17 water tenders, 10 helicopters, 68 hand crews, 13 dozers.

Evacuations: The mandatory evacuation orders for the Loma Prieta ridgeline area including all tributary roads along Summit Road east of Soquel San Jose Road to Ormsby Fire Station. This includes Loma Chiquita, Casa Loma, and Loma Prieta Way.

Evacuation centers: Morgan Hill Presbyterian Church, 16970 De Witt Ave., Morgan Hill.

Road closures: Loma Chiquita, 1 mile east of Highland Way; Summit Road at Ormsby Cutoff; Casa Loma west McKean Road.

Source: Cal Fire

Source: Cal Fire