By Steve Gorman
LOS ANGELES (Reuters) - The battle to tame California's fiercest wildfire this year, the big Rocky blaze north of Napa Valley wine country, neared a turning point on Thursday as ground crews fighting the flames for an eighth day steadily extended their control lines.
The containment level for the blaze, a measure of how much of its perimeter has been firmly enclosed within fire breaks hacked through unburned vegetation, rose to 45 percent on Thursday evening - more than double what it was two days earlier.
Fire crews had made significant headway since Tuesday after triple-digit temperatures abated and humidity rose.
"The last couple of days have actually been good days for us, with the weather cooperating," California fire spokesman Daniel Berlant said. "If we can make it through today, we definitely will have turned a corner and will have gotten an upper hand on the fire."
The fire's overall footprint held steady from Wednesday at 69,600 acres burned, while the number of structures listed as immediately threatened declined slightly to just over 6,500, down from nearly 7,000 the day before.
The tally of property losses edged up, from 91 to 96 structures destroyed, including 43 homes. But the California Department of Forestry and Fire Protection (Cal Fire) reported that damage inspections were finished and barring further spread of fire, no additional losses were expected.
Berlant said it was too soon to declare victory. A key test will be if containment lines hold once gusty winds and hotter, dryer weather returns as forecast.
A threat of lightning on top of warmer weather heightened vigilance on Thursday evening, said Cal Fire spokesman Rick Frawley.
More than 13,000 people remained under evacuation orders or advisories in the fire zone, which spans parts of three counties in the rural ranch lands 110 miles north of San Francisco. Smoke from the blaze has been visible as far away as the Napa wine-making region 80 miles to the south.
Governor Jerry Brown, who declared a state of emergency last week, visited the perimeter of the fire zone on Thursday.
How the Rocky Fire ignited on July 29 was still undetermined, but the blaze is one of more than two dozen conflagrations that erupted across the state during the past two weeks, many of them following a flurry of dry lightning strikes.
The fires have been fed by thickets of chaparral, scrub oak and timber left desiccated from four years of severe drought. Drought conditions have stoked extraordinary wildfire activity this summer in other Western states, including Oregon, Washington, Idaho and Alaska.
(Reporting and writing by Steve Gorman from Los Angeles; additional reporting by Mary Wisniewski in Chicago; Editing by Cynthia Osterman and Nick Macfie)