File:California Wildfires (MODIS 2021-10-05).jpg

English: On October 3, 2021, smoke from the Windy and KNP Complex fires in Tulare, County, California shrouded the San Joaquin Valley with a dense gray haze. The Moderate Resolution Imaging Spectroradiometer (MODIS) on board NASA’s Terra satellite acquired this true-color image on that same day. Multiple red “hot spots” mark the areas where the thermal bands on the MODIS instrument detected high temperatures. In this case, the scattered hot spots in the southeastern portion of the image mark actively burning areas along the leading edges of the two large fires, rather than many different fires. As fires grow, the fuel in the center is consumed first, so expansion occurs along the edges. When fires are very large, there can be many active areas well away from the center.

Both the KNP Complex and Windy fires were ignited by lightning strike on September 9-10. The KNP Complex is the more northerly of the two and is burning in the Sequoia and Kings Canyon National Park and Sequoia National Forest. The September lightning storms initially ignited two fires in that location—the Paradise and the Colony Fires—which subsequently merged to create the KNP Complex. As of October 4, this complex has burnt 67,708 acres and is only 11 percent contained, with more than 1,500 personnel working the incident. There are multiple evacuation orders in effect, including new ones issued late on October 4. The Windy Fire ignited on September 9 a quarter mile southeast of Cholollo campground and two miles south of Camp Nelson. InciWeb Incident Information System reports that as of the evening of October 4, the fire has affected 95,345 acres and has reached 70 percent containment. It has continued to spread throughout the day, but with more than 1,900 personnel working the fire and a forecast for lower temperatures and increasing humidity as a cold front moves across the region in the next few days containment is predicted to be October 14.

The San Joaquin Valley Air Pollution Control District warns residents being impacted by smoke to remain indoors to reduce their exposure to particular matter (PM) emissions. Particulate matter can trigger asthma attacks, aggravate chronic bronchitis, and increase the risk of heart attack and stroke. While common cloth and paper masks being used as protection form COVID-19 may not be sufficient protection from wildfire smoke inhalation. For outdoor workers and other individuals that simply cannot remain indoors, state health authorities recommend the use of N95 facemasks as feasible. The Air Quality Alert is expected to continue through October 7, when a low-pressure system moving over the Valley is forecast to improve dispersion.