YAKIMA — There’s no relief in sight for firefighters battling several large wildfires in Washington state, and a lightning storm forecast to sweep through the region Saturday could ignite even more blazes and bring little to no rain.

For weeks, thousands of firefighters have been working to steer the fires away from scattered hillside homes and entire communities, awaiting the fall rains or mountain snow that typically end the wildfire season. The fires are burning on 143 square miles of parched forest, brush and grass.

Thick smoke has blanketed the immediate area of the fires and beyond, forcing one school district to cancel classes entirely. State health officials sent more than 20,000 respirator masks to the region in anticipation of possible shortages.

And still, the wait continues.

Saturday’s storm could bring lightning to western Washington and up and down the Cascade Range, with the hardest-hit area likely to be the central region, National Weather Service meteorologist Steven Van Horn said.

The storm is likely to bring very little precipitation, he said. Significant rainfall or snow that might douse the fires is not expected any time soon.

That’s unwelcome news for thousands of firefighters already battling several large wildfires there — and dozens of small ones — that were sparked by a lightning storm earlier this month.

So far, firefighters have largely been able to protect homes and other structures. Residents of 161 homes north of Ellensburg, about 100 miles southeast of Seattle, have been urged to leave because of fires.

Several fires there have already burned together to create one blaze covering more than 47 square miles. Fire officials said an air inversion that limited visibility and kept aircraft from helping fight the Table Mountain Fire on Friday also limited fire activity for most of the day.

The Table Mountain fire was threatening to merge with another large blaze southwest of Wenatchee. U.S. Highway 97 was closed over Blewett Pass for nearly 12 hours Friday as firefighters worked to burn dry fuel and take down dead trees.

Some forest land in the fire’s path hasn’t burned in decades, and trees have been killed or removed of their foliage by outbreaks of mountain pine beetle and Western spruce budworm, fire spokeswoman Connie Mehmel said.

“We’re not trying to get them to burn together, but it just isn’t realistic” to stop them, she said. “In some ways, we can more easily manage these fires if they burn together with just one perimeter.”

In the meantime, crews were just working to secure lines in case the coming storm brings high winds, she said.

“And if we get new starts, we’ll have to deal with them as they arrive,” Mehmel said.

Smoke from the fires is pouring across Eastern Washington, obscuring the air 200 miles away in Spokane. State officials have warned of hazardous air quality in Ellensburg and Wenatchee from the thick smoke. They are advising residents to stay indoors, limit physical activity and keep doors and windows closed.

One school district canceled classes for the week because of the smoke, and several high schools postponed or relocated outdoor sporting events. Central Washington University also moved its Saturday football game against Azusa Pacific from Ellensburg to Bothell.

In Yakima, organizers canceled the annual Sunfair Parade to open the Central Washington State Fair due to the poor air quality.