Crews dug firelines and reinforced others on the northwestern edge of a wildfire that crept toward hundreds of forest homes in Southern California on Thursday.

The fire moved slowly, feeding on dense stands of pine and thickets of chaparral, sumac and manzanita in the Los Padres National Forest, where the blaze has burned 159,281 acres, or nearly 249 square miles, northwest of Los Angeles since Labor Day.

Click Here to visit FOXNews.com's Natural Disasters Center.

FOXNews.com's wildfires photo essay

"We're pretty optimistic. We're getting some lines around the fire. It's starting to look pretty good," said Ventura County fire Battalion Chief Bryan Vanden Bossche. "This is one of the days we've had the least amount of (fire) activity."

The National Weather Service predicted low humidity during afternoon hours through Friday. That could dry out brush and make it easier for the fire — the fifth-largest wildfire in recorded state history — to make an explosive advance.

"The line will be tested," said Melody Fountain of the U.S. Forest Service.

Winds were light but erratic Thursday and lookouts were posted to warn crews in case the fire suddenly changed direction. "It's extremely dangerous for them to be in there," said Ventura County fire Capt. Barry Parker.

Dozens of fire engines continued to guard homes in the mountain communities. Authorities continued to recommend evacuation of Lockwood Valley and nearby communities, although many people chose to remain.

More than 4,500 firefighters, aided by aircraft, were fighting the blaze, which was burning at elevations up to about 6,000 feet up in the mountains. The blaze was 43 percent contained

The fire has only destroyed two barns, two outbuildings, three trailers, an unoccupied cabin and five vehicles.

Firefighting costs have topped $53 million. The Federal Emergency Management Agency has authorized the use of federal funds to cover some expenses.