An air quality health alert was issued Wednesday afternoon by the Tuolumne County Public Health Department due to smoke drifting north and northwest from the out-of-control Ferguson Fire burning about 60 miles southeast of Sonora, west of Yosemite in the Merced River Canyon.

“Smoke accumulation has rendered air quality unhealthy for sensitive groups in some areas and unhealthy to very unhealthy in other areas for everyone,” county public health staff said in a statement.

Tuolumne County geography may trap smoke in certain valleys and basins, county public health staff said. They did not specify which parts of the county were being hardest-hit by Ferguson Fire smoke.

Earlier Wednesday, the county air pollution control officer declared air quality unhealthy for elevations between 3,000 and 6,000 feet. At lower elevations, daytime highs were predicted to approach or exceed 100 degrees Fahrenheit in places like Angels Camp, Columbia, Sonora, Jamestown and Chinese Camp.

The current heat wave was expected to bring highs of 102 degrees to the Ferguson Fire burn, where more than 1,800 firefighters were toiling to get lines around the blaze in steep terrain with pockets of heavy timber killed by bark beetles.

As of Wednesday afternoon, the Ferguson Fire and its massive smoke volumes were being monitored by NASA and the USFS Wildland Fire Air Quality Response Program. A smoke forecast issued Wednesday morning said inversion was expected to continue to hold smoke in the foothills until mid-afternoon, and smoke will continue to be heavy from early morning until the inversion breaks.

While air quality was considered unhealthy in Tuolumne County, it was labeled very unhealthy in locations closer to the Ferguson Fire, including Yosemite Village in Yosemite National Park, El Portal west of Yosemite, Ponderosa Basin, Midpines, Bootjack and the town of Mariposa.

When the air quality index is very unhealthy, everyone should avoid prolonged exertion and heavy exertion.

High-altitude wind shifts were pushing unhealthy levels of smoke from the Ferguson Fire near El Portal northwest into Sonora and the Highway 49 corridor, the director of the Tuolumne County air pollution control district said.

“Over the next couple of days we’re going to have similar conditions to what we’re seeing today,” Gary Stockel, air pollution control officer, said Wednesday in a phone interview. “So we're going to have unhealthy air conditions in the 3,000 to 6,000 foot elevations.”

As of 11 a.m. Wednesday, smoke from the Ferguson Fire was creating hazy conditions in downtown Sonora and obscuring distant landmarks, including ridges above the Dragoon Gulch Trail southwest of downtown.

Stockel said people who are in sensitive groups definitely should stay inside.

“That would be folks who suffer from asthma, the elderly or anyone else with a compromised lung system,” Stockel said.

Stockel said people in west Tuolumne County can expect air quality conditions to improve in the late afternoon and evening. They should keep in mind that Wednesday was the first day of a cycle with unhealthy morning to mid-afternoon air quality for the next several days.

“Currently we have higher elevation transport winds moving smoke north from the Ferguson Fire,” Stockel said. “That changed direction last night. Prior to last night those winds were moving smoke to the south.”

There were no county plans to open cooling centers, Michelle Jachetta, the county health program supervisor and emergency preparedness coordinator, said Wednesday afternoon.

As of Wednesday afternoon, the Ferguson Fire was mapped at more than 17,300 acres. The blaze threatens more than a hundred homes. A Cal Fire bulldozer operator died fighting the fire on Saturday. Two other firefighters have been injured.

Incident commanders were still investigating the cause of the fire, which started Friday night next to Highway 140. Cal Fire is investigating the death of 36-year-old Braden Varney of the Madera-Mariposa-Merced Unit.

As of Wednesday afternoon, containment of the Ferguson Fire was estimated at 5 percent.