YOSEMITE NATIONAL PARK, Calif. — Smoke from a wildfire in and around Yosemite National Park is hampering both suppression efforts and the views sought by holiday weekend tourists.


Park spokeswoman Kari Cobb said smoke from the 2-week-old blaze obscured Yosemite Valley for the first time Saturday. The valley is home to the park's most popular landmarks.


And weather forecasts indicate the dense blanket could stick around until Monday.


Meanwhile, U.S. Forest Service spokesman Mark Healey says firefighting aircraft remained grounded Saturday morning because of low visibility caused by the smoke.


Healey says officials are concerned about a 150-acre spot fire that crossed a road and prompted an evacuation order for homes near the west entrance of Yosemite.


As of Saturday, the entire wildfire has burned 343 square miles, up from 333 square miles a day earlier.


THIS IS A BREAKING NEWS UPDATE. Check back soon for further information. AP's earlier story is below.


Smoke from a wildfire around Yosemite National Park is causing problems in the San Joaquin Valley, even as firefighters make advances against the massive blaze.


Winds had been blowing dense smoke plumes northeast into the Lake Tahoe area and Nevada but a shift brought them west down to the San Joaquin Valley floor.



Regional air pollution control authorities issued a health caution for San Joaquin, Stanislaus, Merced, Madera, Fresno and Tulare counties. Residents who see or smell smoke were urged to stay inside, especially people with heart of lung problems, older adults and children.


But in signs of progress, By Friday crews had built containment lines around more than a third of the huge forest fire and officials had lifted evacuation advisories in some small communities in the mountainous area,


Also, a few dozen firefighters were released and more could be sent home in coming days, said Daniel Berlant, spokesman for the California Department of Forestry and Fire Protection. More than 4,800 firefighters remained on the scene late Friday.


"We continue to gain the upper hand, but there's still a lot of work to be done," Berlant said.


The 2-week-old blaze burning in the Sierra Nevada northeast of Fresno has scorched 333 square miles of brush, oaks and pine, making it the largest U.S. wildfire to date this year and the fifth-largest wildfire in modern California records. Containment was estimated at 35 percent.


Evacuation advisories were lifted Thursday in Tuolumne City, Soulsbyville and Willow Springs but remained in place for other communities, and evacuations were still mandatory along the fire's southeastern edge.


About 75 square miles of the fire are inside Yosemite but at some distance from the national park's major attractions, including glacially carved Yosemite Valley's granite monoliths and towering waterfalls.


Park officials expect about 3,000 cars a day to pass through gates during the long Labor Day holiday weekend instead of the nearly 5,000 that might typically show. The fire has caused some people to cancel reservations in the park but those vacancies have been quickly filled, officials said.


"Valley campgrounds are still full and skies in Yosemite Valley are crystal clear," said park spokeswoman Kari Cobb.


A 4-mile stretch of State Route 120, one of three western entrances into Yosemite, remained closed, hurting tourism-dependent businesses in communities along the route.


Costs reached $47 million, including firefighters from 41 states and the District of Columbia and significant aviation resources including helicopters, a DC-10 jumbo jet and military aircraft equipped with the Modular Airborne FireFighting System. Aircraft have dropped 1.7 million gallons of retardant and 1.4 million gallons of water.


The fire started Aug. 17 and its cause remains under investigation. It is expected to keep burning long after it is fully contained, and recovery will be extensive. Some 7,000 damaged trees next to power lines will need to be removed by utility crews and 800 guardrail posts will need to be replaced on Route 120, a fire fact sheet said.



Earlier on HuffPost:




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  • Firefighters enter a grove of giant sequoias in Yosemite National Park in this photo made on Sunday, Aug. 25, 2013, and released by the National Park Service on Tuesday. (AP Photo/National Park Service)




  • AP10ThingsToSee - Inmate firefighters walk along state Highway 120 as firefighters continue to battle the Rim Fire near Yosemite National Park, Calif., on Sunday, Aug. 25, 2013. (AP Photo/Jae C. Hong, File)




  • The Rim Fire burns through trees near Yosemite National Park, Calif., on Tuesday, Aug. 27, 2013. (AP Photo/Jae C. Hong)




  • Russell Mitchell


    Firefighter Russell Mitchell, left, monitors a back burn during the Rim Fire near Yosemite National Park, Calif., on Tuesday, Aug. 27, 2013. (AP Photo/Jae C. Hong)




  • The Rim Fire burns through trees near Yosemite National Park, Calif., on Tuesday, Aug. 27, 2013. (AP Photo/Jae C. Hong)




  • A videographer records the Rim Fire burning through trees near Yosemite National Park, Calif., on Tuesday, Aug. 27, 2013. (AP Photo/Jae C. Hong)




  • A smoke plume from the Rim Fire rises nera Yosemite National Park, Calif., on Monday, Aug. 26, 2013. (AP Photo/Jae C. Hong)




  • A helicopter reloads fire retardant as firefighters continue to battle the Rim Fire in Tuolumne City, Calif., on Monday, Aug. 26, 2013. (AP Photo/Jae C. Hong)




  • Aerial Water Drop on Rim Fire


    In this Thursday, Aug. 22, 2013 photo provided by the California Army National Guard on Monday, Aug. 26, 2013, Sgt. Chris Boni, crew chief from the 1-140th Aviation Battalion (Air Assault) from Los Alamitos Joint Training Base (JFTB), releases water to help control the Rim fire below near Yosemite National Park, Calif. The The UH-60 Black Hawk Crews are battling the Rim wildfire, one of the largest in California history, in support of the U.S. Forest Service and CAL FIRE. (AP Photo/U.S. California Air National Guard, Master Sgt. Julie Avey)




  • In this Thursday, Aug. 22, 2013 photo provided by the California Army National Guard on Monday, Aug. 26, 2013, Sgt. Chris Boni, crew chief from the 1-140th Aviation Battalion (Air Assault) from Los Alamitos Joint Training Base (JFTB), releases water to help control the Rim fire below near Yosemite National Park, Calif. The The UH-60 Black Hawk Crews are battling the Rim wildfire, one of the largest in California history, in support of the U.S. Forest Service and CAL FIRE. (AP Photo/U.S. California Air National Guard, Master Sgt. Julie Avey)




  • Smoke clouds and bands of haze from the Rim Fire in the western Sierra Nevada loom up some 20 miles behind the famed granite monolith known as Half Dome, right center, seen from 11,500-foot Mt. Clark in Yosemite Valley in Yosemite National Park, Calif., Saturday, Aug. 24, 2013. (AP Photo/Tami Abdollah)




  • A fire truck drives past burning trees as firefighters continue to battle the Rim Fire near Yosemite National Park, Calif., on Monday, Aug. 26, 2013. (AP Photo/Jae C. Hong)




  • A burned SUV sits in front of a campground destroyed by the Rim Fire near Yosemite National Park, Calif., on Monday, Aug. 26, 2013. (AP Photo/Jae C. Hong)




  • A helicopter drops water over a hot spot while battling the Rim Fire near Yosemite National Park, Calif., on Sunday, Aug. 25, 2013. (AP Photo/Jae C. Hong)




  • A.J. Tevis


    Firefighter A.J. Tevis watches the flames of the Rim Fire near Yosemite National Park, Calif., on Sunday, Aug. 25, 2013. (AP Photo/Jae C. Hong)




  • The Rim Fire burns along Highway 120 near Yosemite National Park, Calif., on Sunday, Aug. 25, 2013. (AP Photo/Jae C. Hong)




  • The Rim Fire burns along Highway 120 near Yosemite National Park, Calif., on Sunday, Aug. 25, 2013. (AP Photo/Jae C. Hong)




  • A smoke rises from smoldering trees as firefighters continue to battle the Rim Fire near Yosemite National Park, Calif., on Sunday, Aug. 25, 2013. (AP Photo/Jae C. Hong)




  • Firefighter Charlie Ferris, of Los Angeles, watches a smoke plume from the Rim Fire near Yosemite National Park, Calif., on Sunday, Aug. 25, 2013. (AP Photo/Jae C. Hong)




  • A firefighter watches for spot fires during a burnout operation while battling the Rim Fire near Yosemite National Park, Calif., on Sunday, Aug. 25, 2013. (AP Photo/Jae C. Hong)




  • Inmate firefighters walk along Highway 120 after a burnout operation as firefighters continue to battle the Rim Fire near Yosemite National Park, Calif., on Sunday, Aug. 25, 2013. (AP Photo/Jae C. Hong)




  • The smoke generated by the Rim Fire rises under a star-filled sky near Yosemite National Park, Calif., on Sunday, Aug. 25, 2013. Fire crews are clearing brush and setting sprinklers to protect two groves of giant sequoias as a massive week-old wildfire rages along the remote northwest edge of Yosemite National Park. (AP Photo/Jae C. Hong)




  • GROVELAND, CA - AUGUST 28: Cows graze in a field as the Rim Fire burns in nearby hills on August 28, 2013 near Groveland, California. Over 3,500 firefighters are battling the destructive Rim Fire that has charred 180,000 acres and has entered a section of Yosemite National Park. The fire is currently 23 percent contained. (Photo by Justin Sullivan/Getty Images)




  • GROVELAND, CA - AUGUST 28: A CalTrans worker takes a break during a tree cutting operation in an area that was burned by the Rim Fire during a media tour of the fire area on August 28, 2013 near Groveland, California. (Photo by Justin Sullivan/Getty Images)




  • GROVELAND, CA - AUGUST 25: A burned car sits on the side of the road after being consumed by the Rim Fire on August 25, 2013 near Groveland, California. (Photo by Justin Sullivan/Getty Images)




  • YOSEMITE NATIONAL PARK, CA - AUGUST 25: Trees burned by the Rim Fire stand on August 25, 2013 in Yosemite National Park, California. (Photo by Justin Sullivan/Getty Images)




  • GROVELAND, CA - AUGUST 25: Flames from the Rim Fire consume trees on August 25, 2013 near Groveland, California. (Photo by Justin Sullivan/Getty Images)




  • GROVELAND, CA - AUGUST 25: U.S. Fish and Wildlife Service firefighter Corey Adams sits on a tree stump as he monitors the Rim Fire on August 25, 2013 near Groveland, California. (Photo by Justin Sullivan/Getty Images)




  • GROVELAND, CA - AUGUST 24: West Stanislaus County Fire firefighters monitor the Rim Fire along highway 120 on August 24, 2013 near Groveland, California. (Photo by Justin Sullivan/Getty Images)




  • GROVELAND, CA - AUGUST 24: A firefighter uses a hose to douse the flames of the Rim Fire on August 24, 2013 near Groveland, California. (Photo by Justin Sullivan/Getty Images)




  • YOSEMITE NATIONAL PARK, CA - AUGUST 24: Smoke from the Rim Fire lingers over the O'Shaughnessy Dam at Hetch Hetchy Reservoir on August 24, 2013 in Yosemite National Park, California. (Photo by Justin Sullivan/Getty Images)




  • YOSEMITE NATIONAL PARK, CA - AUGUST 24: U.S. Forest Service firefighter Chris Brossard monitors a spot fire while battling the Rim Fire on August 24, 2013 in Yosemite National Park, California. (Photo by Justin Sullivan/Getty Images)




  • GROVELAND, CA - AUGUST 25: Flames from the Rim Fire consume trees on August 25, 2013 near Groveland, California. (Photo by Justin Sullivan/Getty Images)




  • YOSEMITE NATIONAL PARK, CA - AUGUST 24: A firefighter uses a hose to douse a spot fire while battling the Rim Fire on August 24, 2013 in Yosemite National Park, California. (Photo by Justin Sullivan/Getty Images)




  • In this undated photo provided by the U.S. Forest Service, the Rim Fire burns near Yosemite National Park, Calif. (AP Photo/U.S. Forest Service)




  • GROVELAND, CA - AUGUST 22: A firefighter from Central Calaveras Fire monitors the Rim Fire on August 22, 2013 in Groveland, California. (Photo by Justin Sullivan/Getty Images)




  • YOSEMITE NATIONAL PARK, CA - AUGUST 22: Smoke from the Rim Fire is visible near the Hetch Hetchy reservoir on August 22, 2013 in Yosemite National Park, California. (Photo by Justin Sullivan/Getty Images)




  • GROVELAND, CA - AUGUST 22: A firefighting helicopter flies in front of a plume of smoke from the Rim Fire on August 22, 2013 in Groveland, California. (Photo by Justin Sullivan/Getty Images)




  • In this undated photo provided by the U.S. Forest Service, the Rim Fire burns near Groveland Ranger Station in Groveland, Calif. (AP Photo/U.S. Forest Service)




  • GROVELAND, CA - AUGUST 22: Firefighters from the Colorado based South Arkansas Fire District monitor the Rim Fire on August 22, 2013 in Groveland, California. (Photo by Justin Sullivan/Getty Images)




  • GROVELAND, CA - AUGUST 22: Firefighters monitor a plume of smoke from the Rim Fire on August 22, 2013 in Groveland, California. (Photo by Justin Sullivan/Getty Images)




  • GROVELAND, CA - AUGUST 22: A U.S. Forest Service firefighter monitors a radio while battling the Rim Fire on August 22, 2013 in Groveland, California. (Photo by Justin Sullivan/Getty Images)




  • GROVELAND, CA - AUGUST 22: A firefighter from the Kern County Rio Bravo Hotshots looks for flying embers while battling the Rim Fire on August 22, 2013 in Groveland, California. (Photo by Justin Sullivan/Getty Images)




  • GROVELAND, CA - AUGUST 22: Firefighters douse hot spots while battling the Rim Fire on August 22, 2013 in Groveland, California. (Photo by Justin Sullivan/Getty Images)




  • GROVELAND, CA - AUGUST 21: Firefighters from Ebbetts Pass Fire District monitor a back fire as they battle the Rim Fire on August 21, 2013 in Groveland, California. (Photo by Justin Sullivan/Getty Images)




  • GROVELAND, CA - AUGUST 21: A firefighter from Ebbetts Pass Fire District uses a drip torch to light a back fire as they battle the Rim Fire on August 21, 2013 in Groveland, California. (Photo by Justin Sullivan/Getty Images)




  • GROVELAND, CA - AUGUST 21: Firefighters from Ebbetts Pass Fire District monitor a back fire as they battle the Rim Fire on August 21, 2013 in Groveland, California. (Photo by Justin Sullivan/Getty Images)




  • GROVELAND, CA - AUGUST 21: A firefighter from Ebbetts Pass Fire District monitors a back fire as he battles the Rim Fire on August 21, 2013 in Groveland, California. (Photo by Justin Sullivan/Getty Images)




  • GROVELAND, CA - AUGUST 21: Firefighters from Ebbetts Pass Fire District monitor a back fire as they battle the Rim Fire on August 21, 2013 in Groveland, California. (Photo by Justin Sullivan/Getty Images)




  • GROVELAND, CA - AUGUST 21: A firefighter from Ebbetts Pass Fire District uses a drip torch to light a back fire while battling the Rim Fire on August 21, 2013 in Groveland, California. (Photo by Justin Sullivan/Getty Images)




  • BUCK MEADOWS, CA - AUGUST 21: Fire consumes trees along US highway 120 as the Rim Fire burns out of control on August 21, 2013 in Buck Meadows, California. (Photo by Justin Sullivan/Getty Images)