Like the vast majority of wildfires , this one, called the Carr Fire, burned initially as a wide but shallow band of flames advancing slowly, like a battalion of infantrymen marching shoulder to shoulder, and left behind charred grass and lightly scorched trees. The Carr Fire was also typical in that it moved according to the dictates of wind, ground slope, and flammable fuels—southeast around a lake, then up a hill, in part because heat rises. Early on that particular morning, the fire had crested a rise above Redding and, with a northwesterly breeze at its back, crawled downhill toward town.
Knapp was finishing up for the day when his friend Talitha Derksen, a wildlife biologist with a daughter close in age to Knapp’s own, sent a text saying that her neighborhood might have to be evacuated. One of the agencies tasked with that judgment call, the California Department of Forestry and Fire Protection—aka CalFire—is one of the world’s largest and most effective wildland firefighting organizations. CalFire bases evacuation recommendations on predictions of where, and how quickly, a flame front will move next. That day, the fire appeared likely to reach the floor of the Sacramento Valley at a subdivision called Land Park, about a mile northwest of Derksen’s house.
Knapp and the others changed plans: They’d meet at Derksen’s, order pizza, and help her get ready to leave in case it came to that. Knapp stopped at his house to grab fireproof Nomex clothing. As he headed to Derksen’s, he considered dropping by the office again to pick up his hard hat and emergency fire shelter—a sort of fire-resistant pup tent—but decided he was unlikely to need them.As he turned onto Derksen’s street, the flame front was a couple of miles away and hidden by trees, but Knapp could see the smoke rising in a straight and tall plume that turned the sun orange. When he arrived at Derksen’s house, she was already packing bags. Knapp, to be sure he knew what they were dealing with, jogged out the nearby Sacramento River Trail for a view. Upriver, on the far bank, he could see red flames torching gray pines and scrubby oaks.
Knapp was shooting photos when he noticed something odd: The wind where he stood blew out of the south, into the fire, but the flame front still moved the other way, driven by that northwesterly at its back. Then he saw something else: Portions of the smoke plume swirled in different directions, as if beginning to rotate.
Knapp knew this could signal a once rare and dangerous phenomenon known as plume-driven fire, in which a fire’s own convective column of rising heat becomes hot enough and big enough to redirect wind and weather in ways that can make the fire burn much hotter and, with little warning, spread fast enough to trap people as they flee.
As Knapp ran back down the trail, he passed neighbors walking and recommended they turn around. But even he had no idea how much peril they were all in. At the house, as Derksen left, Knapp and others hosed down the roof and rain gutters and cleared the yard of flammable material like cardboard boxes and lawn furniture. Knapp was the last person there, spraying water on the fence and yard.