The Oak Fire that has ravaged more than 18,000 acres and destroyed 40-plus structures in Mariposa County is now 26 percent contained.
Centered in Midpines, just 60 miles due east of Turlock, the fire has adversely impacted the air quality in most of the eight counties that make up the San Joaquin Valley Air Pollution Control District, according to Cassandra Melching, the outreach and communications representative for the APCD.
However, Stanislaus and San Joaquin counties are not among those with air quality affected by the fire that started June 22.
Merced, Madera, Fresno, Tulare and Kern counties, as well as Sequoia National Park and Forest were solidly in the “unhealthy for sensitive groups” range, while Stanislaus and San Joaquin remain in the moderate range.
Merced is expected to return to the moderate range today.
An index of 0 to 50 is considered good air quality, while moderate is 51 to 100 Unhealthy for sensitive groups (asthmatics, the elderly, young children) is 101-150; unhealthy for all groups is 151-200, extremely unhealthy is 201-300 and anything above 301 is classified as hazardous.
San Joaquin County is very nearly in the good zone, with an index of 51, while Stanislaus County has an index of 87, firmly in the moderate category. Kings County also is in the moderate zone, but just barely.
The Washburn Fire, which started July 7 and also centered in Mariposa County and now 87 percent contained, has also been a contributor to the decrease in air quality.
The air quality is not expected to reach the levels seen in the summer of 2020 when the SCU fire centered in Diablo Canyon near Patterson — just about 30 miles west of Turlock — and the LNU fire near Napa combined to deliver some of the worst air conditions in recent memory. At times, ash from those fires could be seen falling from a brownish-gray sky, while the sun appeared to be tiny red dot battling to break through the haze as counties up and down the state reported an air quality index well into the hazardous zone.
Of course, the intensity of the blaze and shifting winds could change conditions rapidly.