Wildfire smoke chokes Yosemite, air quality reaches unhealthy level

Wildfire smoke chokes Yosemite National Park on Sept. 5, 2017. Wildfire smoke chokes Yosemite National Park on Sept. 5, 2017. Photo: Courtesy Yosemite National Park Photo: Courtesy Yosemite National Park Image 1 of / 59 Caption Close Wildfire smoke chokes Yosemite, air quality reaches unhealthy level 1 / 59 Back to Gallery

The air quality in Yosemite National Park reached unhealthy levels Wednesday morning as smoke from multiple wildfires choked the valley.

The national park posted an eerie image (see above) of the park on Facebook on Tuesday night showing the valley's bleak brownish haze. Only the trees and a meadow in the foreground are visible, while Half Dome and the park's granite peaks are obscured.

"What makes the smoke settle in the valley?" the Facebook post explains. "When air gets cold, it becomes more dense. The cold air flows down canyons and other low spots (like Yosemite Valley), carrying the smoke particles with it. When the air warms up and conditions are right, the rising warm air carries the smoke particles upward."

The Empire and South Fork wildfires are burning in the park as well as several smaller fires. The nearby Peak and Railroad fires are contributing to the smoky conditions, said Mike Kochasic, a meteorologist with the National Weather Service office in Sacramento.

Related: Yosemite trails, road shut down as fire reaches deeper into grove of giant sequoias

"Right now we're coming out of a period where we had really high pressure over us and that creates a lot of stagnant air and the air quality becomes bad from pollution alone," Kochasic, said. "When you add wildfires to that, it gets really bad. You have reduced visibility and poor air quality."

The Yosemite National Park website confirmed Wednesday morning that air quality levels had reached unhealthy levels at the visitor center. The park referred visitors to more detailed information on a U.S. Forest Service site indicating the Wawona area was at a hazardous level, while Yosemite Village, Yosemite West, Foresta, Tuolumne Meadows and El Portal would all remain unhealthy through the day with some clearing in the evening.

The smoky conditions are expected to improve Thursday.

Access to Yosemite via Highway 41 from Fish Camp, Oakhurst, or Fresno, is closed due to the Railroad Fire. Visitors are advised to travel to use Highway 49 to Mariposa, then Hwy 140 to Yosemite.