REDDING, Calif. (AP) — A rare fire tornado that raged during this summer's deadly Carr Fire in Northern California was created by a combination of scorching weather, erratic winds and an ice-topped cloud that towered miles into the atmosphere, according to a study announced Wednesday.

The churning funnel of smoke and flame killed a firefighter as it exploded in what already was a vast and devastating wildfire in July on the edge of Redding, about 250 miles (400 kilometers) north of San Francisco.

The wildfire claimed eight lives and destroyed more than 1,000 homes before it was contained on Au...