Firefighters battling the giant wildfire burning in the Sierra Nevada added a California National Guard Predator drone to their arsenal Wednesday to give them real-time views of flames chewing through rugged forests in and around Yosemite National Park. 
 
 Workers cut trees burn by the Rim Fire along Highway 120 near Yosemite National Park, Calif., on Wednesday, Aug. 28, 2013. The giant wildfire burning at the edge of Yosemite National Park is 23 percent... (Associated Press) 
 
 Firefighter Brandon Wenger stands along Highway 120 while monitoring a backburn during the Rim Fire near Yosemite National Park, Calif., on Tuesday, Aug. 27, 2013. Unnaturally long intervals between wildfires... (Associated Press) 
 
 Two firefighters monitor a back burn during the Rim Fire near Yosemite National Park, Calif., on Tuesday, Aug. 27, 2013. Unnaturally long intervals between wildfires and years of drought primed the Sierra... (Associated Press) 
 
 The Rim Fire burns through trees near Yosemite National Park, Calif., on Tuesday, Aug. 27, 2013. Firefighters gained some ground Tuesday against the huge wildfire burning forest lands in the western Sierra... (Associated Press) 
 
 In this photo provided by the National Park Service, a Merced Grove cabin, next to the giant sequoias, is covered in metal foil by CalFire crews trying to protect structures from the Rim Fire burning... (Associated Press) 
 
 Firefighter Russell Mitchell monitors a back burn during the Rim Fire near Yosemite National Park, Calif., on Tuesday, Aug. 27, 2013. Unnaturally long intervals between wildfires and years of drought... (Associated Press) 
 
 Cattle stand in a field as a smoke from the Rim Fire rises near Yosemite National Park, Calif., on Wednesday, Aug. 28, 2013. The giant wildfire burning at the edge of Yosemite National Park is 23 percent... (Associated Press) 
 
 Firefighter Troy Drouin takes a short break before mopping up hot spots near Yosemite National Park, Calif., on Wednesday, Aug. 28, 2013. The giant wildfire burning at the edge of Yosemite National Park... (Associated Press) 
 
 The MQ-1 unmanned aircraft being remotely piloted hundreds of miles away quickly alerted fire bosses to a new flare-up they otherwise wouldn't have immediately seen. 
 
 "This morning it's allowed us to see a spot fire," said Mike Wilkins, commander of forces at the Rim Fire. 
 
 The 12-day-old Rim Fire continued to grow, expanding to 292 square miles, and containment remained at 23 percent. But increasingly confident fire officials said they expect to fully surround it in three weeks, although it will burn for much longer than that. 
 
 "It's looking better every day," said incident spokesman Glen Stratton. 
 
 While unmanned aircraft have mapped past fires, use of the Predator will be the longest sustained mission by a drone in California to broadcast information to firefighters in real time. 
 
 The plane, the size of a small Cessna, will remain over the burn zone for up to 22 hours at a time, allowing fire commanders to monitor fire activity, determine the fire's direction of movement, the extent of containment and confirm new fires ignited by lightning or flying embers. 
 
 "They're piping what they're seeing directly to the incident commander, and he's seeing it in real time over a computer network," said Lt. Col. Tom Keegan. 
 
 Previously ground commanders relied on helicopters that needed to refuel every two hours. 
 
 The drone is being flown by the 163rd Wing of the California National Guard at March Air Reserve Base in Riverside and is operating from Victorville Airport, both in Southern California. It generally flew over unpopulated areas on its 300-mile flight to the Rim Fire. Outside the fire area it will be escorted by a manned aircraft. 
 
 Officials were careful to point out the images are being used only to aid in the effort to contain the fire. 
 
 In 2009 a NASA Predator equipped with an infrared imaging sensor helped the U.S. Forest Service assess damage from a fire in Angeles National Forest. In 2008, a drone capable of detecting hot spots helped firefighters assess movement of a series of wildfires stretching from Southern California's Lake Arrowhead to San Diego. 
 
 The Rim Fire started Aug. 17 and quickly exploded in size, becoming one of the 10 largest California wildfires on record. Its progression slowed earlier this week when it moved from parts of the forest with thick underbrush that had not burned in nearly a century to areas that had seen fire in the past two decades. 
 
 But it will burn for months, possibly until California's dry season ends this fall. 
 
 "My prediction is it will burn until we see rain," said Hugh Safford, a regional ecologist with the U.S. Forest Service. 
 
 That means the smoke could continue to foul air north of Yosemite in the Lake Tahoe basin and neighboring Nevada, although residents received something of a reprieve Wednesday when for the first time in three days blue sky was sometimes visible through the haze. 
 
 The air quality index in the Reno area still had improved only to the "unhealthy" level and in Douglas County, Nev., school children were kept indoors again when the index registered in the "hazardous" category Wednesday morning. 
 
 The air was clear, however, in the tourist mecca of Yosemite Valley, home to the towering Half Dome and El Capitan rock formations and the 2,425-foot plunge of Yosemite Falls. 
 
 The Rim Fire has destroyed 111 structures, including 11 homes, and posed a threat to ancient giant sequoias. 
 
 The fire also has threatened San Francisco's water supply at the Hetch Hetchy Reservoir, but Stratton said it was burning itself out as it approached and that crews were lighting back burns to push it back into the wilderness. 
 
 ____ 
 
 Associated Press reporter Scott Sonner contributed from Reno, Nev. ||||| GROVELAND, Calif. — On Day 10 of the Rim fire — even as the blaze scorched its way deeper into the northern end of Yosemite National Park — firefighters got their first small break Monday against massive forces of nature. 
 
 As the fire reached higher elevations, climbing out of steep ravines, crews could take their stand on more level ground. Huge air tankers could finally drop retardant on accessible ridges. 
 
 The fire has charred a swath of nearly 161,000 acres — including about 21,000 acres inside the park. It has destroyed at least 23 structures, and threatens two groves of giant sequoias and historical structures in the famed park. But about 25 miles away, the tourist magnet of Yosemite Valley remained safe, surrounded by its famed granite walls. 
 
 The fire is burning hotter and faster than any in modern Sierra Nevada history, firefighters say. Officials say it is the California wildfire they have warned about for years, as modern firefighting techniques have snuffed out forest fires, allowing fuel to build up on the mountain floor. 
 
 "This is it. This is the big one," Yosemite Fire Chief Kelly Martin said. 
 
 Yet containment reached 20% — up from 7% Sunday. 
 
 "The fire will burn until the snow flies," said Tom Medema, a Yosemite National Park interpretive ranger. "But today, we finally had a chance to box it in." 
 
 The most hopeful sign was written in the sky. 
 
 For the last week, each afternoon has brought a towering plume of smoke rising over the flames. Inside the plume are lightning and hail, and when the plume collapses, it sends wind pushing the fire in all directions. They call from noon to 5 p.m. the burning hours. 
 
 On Monday, the weather changed slightly — an inversion layer kept the smoke thick and low just a little longer — but it was enough to chop the plume down to half its size. 
 
 "Today we can finally fight the fire on our terms, said Gary Wuchner, Yosemite National Park's fire specialist. 
 
 From the Rim of the World vista point on California 120, he looked out over a wide swath of the fire's footprint. 
 
 It's a spot where tourists often pull over to take photos of the Tuolumne River and mountains in the distance. There was a kiosk giving the history of fires in the area, but it burned to the ground this week. Still standing were two stone monuments to firefighters killed in wildfires in the area — one in 1987, one in 2004. 
 
 "This is hallowed ground to firefighters," Wuchner said. "We have bad history here." 
 
 The needles on four nearby Ponderosa pines were swept straight back, frozen in the direction the fire pushed them. Far off to the northeast, smoke rose above the Hetch Hetchy Reservoir and around Pilot Peak, a fire lookout tower that is staffed each summer. Due north, the edge of Jawbone Ridge looked like it had been outlined with a black marker where the fire had first spilled over. 
 
 Power lines stretched overhead from still standing towers. But the electricity had been cut. On a hill above the river was the only circle of green in sight: Drew Meadow, the base camp for more than 2,000 firefighters. It has now been attacked by the fire from three sides. 
 
 Wuchner's radio crackled constantly. 
 
 "Need retardant drops immediately," a voice said. 
 
 The fight at the park is to save a historic ranger station, stables, lakeside campsites and two groves of giant sequoias. The ancient trees have withstood many fires over the centuries. 
 
 The fear is that this fire, with so much unnatural fuel sending flames higher, could get to the top of the trees and kill them. Wuchner said they had sprinklers dampening the tops of the sequoias and had wrapped all nearby structures in fireproof material. They do not use fire retardant in the national park. When there are lightning fires within the park's boundaries, officials let them burn, unless they are threatening communities. 
 
 "When it comes to fighting the fire within the park," Wuchner said, "what we're banking on is all the fires that came before." 
 
 diana.marcum@latimes.com 
 
 samantha.schaefer@latimes.com 
 
 joseph.serna@latimes.com 
 
 Times staff writer Robert J. Lopez in Los Angeles contributed to this report. Marcum reported from Groveland, Schaefer and Serna from Los Angeles.
– The giant Rim fire near Yosemite National Park has now scorched an area the size of Chicago and is still growing, but firefighters are making steady progress. Officials say the fire is now around 20% contained and the 3,700 firefighters battling it are gaining ground as the blaze climbs out of steep ravines. "The fire will burn until the snow flies," a park ranger tells the Los Angeles Times. "But today, we finally had a chance to box it in." Only around 2% of the park itself has burned and though more of it will burn, authorities have vowed to do everything in their power to protect the iconic Yosemite Valley. The fire has been raining ash on the reservoir that supplies San Francisco with most of its water, but officials say it has not sunk as far as the intake valves and the city's supply should not be affected, the AP reports. As crews continue to bulldoze firebreaks and burn vegetation in the fire's path, biologists are beginning to assess the blaze's effect on wildlife. Bald eagle nests in the area are being monitored, and a group of endangered turtles has been found stranded near where their marshy habitat burned. "We're hoping to deliver some water to those turtles," a Forest Service biologist says. "We might also drag some brush in to give them cover."