As calendars turned from September to October, cooler weather may have given many Californians the idea that the brutal fire season of 2018 is over.

But nothing could be further from the truth, according to fire experts and state fire statistics. October is actually the most dangerous month historically for wildfire risk in the state.

Seven of the 10 worst wildfires in recorded California history, measured by the number of structures burned, have occurred in October. So have the three deadliest, ranked by number of people killed, according to Cal Fire, the state's primary firefighting agency.

"We know what happens this time of year," said Cal Fire Deputy Chief Scott McLean. "We have historical knowledge of what can take place. It's not if. It's when."

October fires have spread death and destruction more than wildfires in any summer month. The Tubbs Fire last year in Napa and Sonoma counties burned 5,636 structures, the most in state history, and killed 22 people. The 1991 Oakland Hills Fire killed a record 25 people and destroyed 2,900 homes and other buildings. And the Cedar and Witch fires, which ravaged San Diego County in 2003 and 2007, incinerated a combined 4,470 structures and killed 17 people. All occurred in October.

There are two primary reasons, experts say: Lack of rain and strong, dry winds.

Unlike in most other states, it almost never rains in the summer in California.

As part of California's Mediterranean climate, most rain ends in April every year, and apart from a few light sprinkles, doesn't begin again in earnest until November. That means by the time October arrives, nearly six months has passed without rain.
As a result, grass, shrubs and trees are usually at their driest condition of the year in October.

Generally scientists say such small amounts of rainfall, as what fell in the state last week, are not enough to significantly reduce fire risk.

"Until we get a bunch of rain, we're still in fire season," said Craig Clements, director of the Fire Weather Research Laboratory at San Jose State University. "If it starts warming up this month, it will get worse."

Clements and his students regularly sample the amount of water in chamise, a common flowering shrub, to determine fuel moisture levels.
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.

(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.)

Those dry conditions mean that with any kind of spark, flames can spread quickly.

And in the fall, wind danger increases. Because of seasonal weather patterns, strong winds blowing west from dry inland areas like 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."

Hot, dry, fast winds spread most of California's deadliest blazes.
Sandra Younger lost her home in Wildcat Canyon, 20 miles east of San Diego, in the Cedar Fire in late October 2003.

She remembers waking up at 3 a.m., seeing flames across the canyon and feeling the howling winds. She and her husband, Bob, grabbed family photos, their two Newfoundland dogs and pet cockatiel bird, and she drove down the narrow road out of the canyon, barely able to see the road in the heavy black smoke.

"The fire came right down the canyon. It was incredibly windy," she said. "Crazy windy. There were ashes in the wind. Embers were blowing everywhere. There were tornadoes of embers."

Some of her neighbors became trapped.

"They jumped into their pools," said Younger, who wrote a book, "The Fire Outside My Window," about the experience. "There were snakes, mice, rats and rabbits in there with them. All the animals jumped in to save their lives."

Twelve of her neighbors died in the inferno, which investigators later said was caused by a hunter who became lost and set a fire to signal rescuers.

Younger and her husband rebuilt their home and still live in the same area today.

Every year, when October rolls around, Younger has advice for California residents, particularly those living in fire-prone areas.

"People should be ready to leave at any moment," she said. "They should have a bag packed and be incredibly aware of the news and weather when there is a red-flag warning. And if they hear of a fire starting, they should leave. They shouldn't try to be garden-hose heroes."

Climate change is increasing California temperatures, further drying out vegetation and lengthening the traditional fire season. A record period of hot, dry winter weather last December, combined with record Santa Ana winds, led to the Thomas Fire, which burned more than 1,000 structures in Santa Barbara and Ventura counties, charring 281,000 acres and causing $2.2 billion in damage.

Red-flag warnings — which the National Weather Service calls when temperatures rise, humidity falls and winds pick up — have been present recently in the Bay Area. Last week, there were red-flag warnings for the East Bay Hills and North Bay.

McLean noted that fire risk remains critical until steady rain soaks the vegetation, usually in November and December.

"We have a challenge getting the public to realize how severe red-flag warnings are," he said. "Treat it like tornadoes and hurricanes in the Midwest. Last year 46 people died in fires in California. People need to know to be prepared to evacuate on a moment's notice."