More howling, whipping, fire-stoking winds have arrived in Los Angeles. They are expected to strengthen by dawn and may blow up to 70 miles per hour. Some gusts could rekindle parts of the major blazes tearing through the city’s hills and suburbs. Others could start new fires.

It may seem hard to understand why the combined resources of the federal government, California and Los Angeles haven’t been able to defeat the wildfires after a week of fighting them.

The winds are a major reason. The gusts hurl embers across great distances, spreading fire quickly and thwarting efforts to pinch it off. Planes and helicopters that spray water and flame retardant can’t fly. Firefighters on the ground can’t battle the flames on streets and hillsides without fear they’ll be incinerated.

At their peak, the winds have forced firefighters to focus on something else: evacuating residents. “You’re just trying to keep people alive,” Lenya Quinn-Davidson, a fire expert in Northern California, said.

How to stop a fire
When forests and grasslands ignite, crews follow a strategy called anchor and flank.

They find a safe spot, or anchor point, upwind of the blaze. Then they attack from the edges: They douse the flames with hoses and remove anything flammable from the fire’s path. They use power tools to thin the vegetation or — for the bigger stuff — reduce it to ash with small controlled burns. That’s called a fire line. The advancing blaze stops when it reaches the fire line and finds nothing else to consume.But it’s incredibly hard to anchor and flank in strong winds. Even a spot that seems safe won’t remain safe for long. Flying embers can soar miles away from the fire’s front, meaning the danger spreads too quickly for firefighters to keep up.

“Fires under these conditions — they’re not moving on the ground” as a normal fire would, said Hugh Safford, a fire ecologist at the University of California, Davis. “They’re moving in the air.” That’s why some wildfires in Southern California can’t be stopped until the desert winds, known as the Santa Anas, recede.

Urban warfare
The Los Angeles inferno adds another difficulty: an urban tinderbox. When embers float from home to home on a crowded street, there’s no way to create fire lines to interrupt the flames. “All of the things that we have in our houses — drapes, couches, carpet — all of a sudden that stuff can ignite really rapidly,” Rick Connell, an officer with the U.S. Forest Service, said.And winds don’t just ground firefighting aircraft. They also make the water and fire retardants they spray less effective. Gusts turn the liquid into mist by the time it hits the ground, where it does little to smother the blaze. Even in the best circumstances, retardants can do only so much. “If you’ve already got 100-foot flames, you’re just wasting money,” Connell said.

Over the last week, Los Angeles deployed more firefighters and received additional air support, including from the military. “We’re absolutely better prepared,” the county’s fire chief told reporters on Monday.

But the experts I interviewed said it would be unrealistic to expect fires of this size to be contained in just a week. For now, the best hope may be to wait until the current winds slow down.