(CNN)Seven Western states are under air quality alerts due to raging wildfires, which have forced thousands to evacuate and destroyed hundreds of homes.
The 92 large wildfires burning in the US have scorched more than 2.5 million acres, according to the National Interagency Fire Center, and their smoke has put thousands under poor air quality alerts.
Areas of California, Nevada, Oregon, Colorado, Wyoming, Idaho and Montana were under air quality alerts Wednesday, according to the National Weather Service (NWS).
Thick smoke blanketed the resort communities of Lake Tahoe this week as the Caldor Fire burning east of Sacramento, California, continued to swell.
And in Reno, Nevada, residents were encouraged to stay indoors due to historically bad air quality.
Nevada's Washoe County -- home to Reno -- saw its poorest air quality on record two days in a row, county health officials said Tuesday. The average air quality index for fine particles reached 251 Sunday, which is considered "very unhealthy," and on Monday, the index number jumped to 291, the Washoe County Health District said.
Smoke from the fires is expected to remain a problem for the area, CNN meteorologist Michael Guy said, as it lingers specifically in portions of the Intermountain West, southern Oregon and the Great Basin, which includes areas of western Nevada.
"For the rest of this week, it looks like smoke will continue to be a problem for portions of the West," Guy said. "Another storm system will approach the Pacific Northwest during the day, allowing winds to shift and some areas to clear. However, smoke remains to be an issue across the region as the general weather pattern does not look to change through the end of this week."
For those in Oregon, the NWS advised they stay inside with windows closed when smoke levels are high.
"Wildfires burning in the region combined with forecast conditions will cause air quality levels to fluctuate and could be at unhealthy levels," the NWS wrote in its Oregon alert.
One of the most concerning fires for firefighters in California is the Caldor Fire in El Dorado County.