Air quality in the San Joaquin Valley is predicted to be at its most unhealthy level in a month Friday as 104-degree heat and stagnant air combine to trap pollution.
Air officials have issued a "very unhealthy" forecast for Fresno County, while the air in Merced, Kings, Tulare and Kern counties earns an only slightly better "unhealthy" rating.
Fresno's air quality index rating, a measure of ozone, particle pollution, carbon monoxide, sulfur dioxide and nitrogen dioxide, is 203 Friday. When values reach 201, the San Joaquin Valley Air Pollution District issues an alert that even healthy people might experience serious effects.
People are advised avoid outdoor activity from 11 a.m. until 8 p.m., peak ozone hours.