After last month's deadly Northern California wildfires, atmospheric scientist Cliff Mass scanned old weather forecasts, searching for clues.
In two high-resolution weather models for Oct. 8, he found ample warning of the crucial ingredient for the firestorm that swept across parts of eight counties, claiming 43 lives and incinerating more than 8,000 buildings.
"I said, 'Oh my God, look at the winds,' " recalled Mass, a University of Washington atmospheric sciences professor who writes a popular weather blog. "What if people were paying attention to this? What could they have done?"
The causes of the October conflagrations are under investigation. But for a number of the fires, the prime suspects are sparking power lines and electrical equipment downed by winds that gusted to more than 70 mph.
"It was a wind event, a sudden onset and pretty sudden die-down," Mass said. "So if you shut the power down for nine hours … it could have been a whole different world."
For years the state's primary way of dealing with its endemic wildfire threat has been to mandate vegetation clearance around homes in high fire-hazard zones and require the use of fire-resistant building materials in new construction.
But as California puts more people and houses on one of the planet's most flammable landscapes and the grim list of deadly wildfires grows longer, some experts say it's time to take stronger steps.
Among them: Ban development in wind corridors where wildlands repeatedly burn; bury utility lines in the backcountry; preemptively shut down power lines and close public lands during extreme wind events to prevent ignitions — the vast majority of which are caused by people or equipment.
"In Southern California, every single year the conditions are there for a severe wildfire," said Alexandra Syphard, senior research scientist with the nonprofit Conservation Biology Institute. "You have Santa Ana wind conditions every year. You have summer drought every year, high temperatures.
"What it takes is an ignition to happen at the same time," she added. "And since ignitions are caused by humans, that is something under our control."
Whether they're called the Santa Anas, diablos or sundowners, withering winds from the east invariably drive California's most horrific wildfires. They blast down mountainsides and fan sparks into unstoppable infernos.
Thanks to advances in weather modeling, these hot breaths of nature are more predictable than ever.
"There are certain corridors where the winds tend to travel," said Alex Hall, a UCLA professor of atmospheric sciences who has helped map Santa Ana wind corridors in Southern California. "We also have the ability to predict event by event where the winds are going to be the strongest."
But the growing sophistication of wind mapping and forecasting isn't reflected in the state's wildfire policies.
"I often hear people say that if we construct our buildings correctly and put enough defensible space around it, then we don't need to worry about where you put the houses," Syphard said.
"But they don't necessarily fireproof your house. You can see that by some of the houses that burned in recent years," added Syphard, whose research has linked wildfire losses to the location and spatial arrangement of houses.
In recent years, the state has made some moves to factor wildfire into land-use planning. Under a 2012 law, cities and counties are supposed to consider wildfire risk and consult with the California Department of Forestry and Fire Protection when they update their general plans and approve subdivisions.
Yet there appears little inclination to place especially fire-prone areas off limits to development.
"We have to consider property rights," said Mitch Glaser, an assistant administrator in the L.A. County Department of Regional Planning.
The county has required fire-related changes in the layout and size of subdivisions and zoned the backcountry to avoid isolated, large-scale housing projects, Glaser said. But he didn't know of any development application that was denied because of wildfire risk.
The building continues even in areas where it is virtually guaranteed that a wind-whipped fire will roar through sooner or later.
Take the five-mansion compound that U2 guitarist the Edge plans to erect on a rugged coastal hillside in Malibu, an oft-scorched corridor for Santa Ana winds.
"The placement of homes on a ridgeline documented to have burned at least six times between 1942 and 2010 makes it almost certain the ridgeline will burn again in the near future," the National Park Service warned in comments to the California Coastal Commission, which approved the project in 2015 after years of controversy over its impact on coastal views and environmentally sensitive habitat.
A few highly flammable parts of the world are taking tougher stands. National planning regulations in France now require communities in the country's fire-prone south to bar development in certain high fire-hazard zones.
"It's not terribly popular. But they do have the ability to make that happen," said Susan Kocher, a natural resources advisor with the UC Cooperative Extension who spent a sabbatical in France and recently published a research paper on the topic.
In California, land-use planning is primarily a local responsibility.
"Local municipalities are so concerned about their tax base and private property rights and making money that they're not addressing the real risks," said Richard Halsey, director of the California Chaparral Institute.
Development should be barred in some areas, or if it's allowed, residents should be required to "sign a waiver — we don't want fire protection," Halsey argued. "I don't know if politically that's ever going to happen."
Bill Stewart, co-director of UC Berkeley's Center for Fire Research and Outreach, says it's time to stop installing above-ground power lines to serve rural residences.
"We're going to have to go underground or not have power lines and have people on pure solar and batteries … because they get knocked down," he said.
San Diego Gas & Electric Co. took another tack after the utility was hit with fines and huge settlement costs in the wake of devastating 2007 wildfires caused by its sparking electrical equipment.
The company spent $1.7 million to install 170 weather observation stations on backcountry poles, creating what it calls one of the country's densest weather monitoring networks.
Every 10 minutes, the stations transmit data to the utility on wind speed and direction, temperature and humidity.
When the Santa Anas start blowing, the company's three meteorologists monitor the network around the clock. Utility crews and contract firefighters are dispatched in advance to areas where the strongest winds are forecast.
Since the program started, SDG&E says, it has turned off power to portions of its distribution system 16 times for public safety reasons. The shut-offs have affected a relatively small number of customers, a total of 1,000, who received telephone alerts of impending outages.
The network has yielded a wealth of new information about regional wind patterns.
"A lot of what people knew was anecdotal," said SDG&E senior meteorologist Steve Vanderburg. "But once you actually install the weather stations and start looking at what's going on, you see that there's a big difference between reality and anecdotal information."
It turns out the county's strongest winds don't blow through passes and canyons, as previously thought. The monitoring has also documented remarkable variability in wind strength across relatively short distances.
In one Santa Ana event, Vanderburg said, gusts of 91 mph were measured at the utility's Sill Hill weather station while a mile to the south they were half that.
No other utility in the state has a similar monitoring system.
After the 2007 fires, SDG&E also worked with the U.S. Forest Service and UCLA scientists to develop the Santa Ana Wildfire Threat Index, which is publicly available online.
Launched in 2014 and managed by federal agencies, the index uses weather data and information on vegetation moisture levels to rank upcoming Santa Ana events according to the potential for a large fire.
On Oct. 24, when one of the strongest Santa Ana events in years hit Southern California, the index rated the wildfire threat in Los Angeles and Ventura counties as "high," one step below the top ranking of "extreme."
"We want to tell people this is a day when you may have to evacuate your home," said Forest Service meteorologist Tom Rolinski, who helped devise the index.
They didn't have to. There were no major fires — this time.