A lightning storm forecast to sweep through the central Cascades and valleys Saturday could ignite even more blazes and bring little to no rain.

The National Weather Service says a red flag warning is in effect from 5 a.m. on Saturday to 6 a.m. on Sunday for "abundant lightning and dry fuels."

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.

The fires burning in central Washington were expected to kick up a little bit Friday with high temperatures and unstable conditions, though the smoke could clear a little bit, National Weather Service meteorologist Steven Van Horn said.

But 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, he said.

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 nearly 47 square miles, and the fire was threatening to merge with another large blaze southwest of Wenatchee. U.S. Highway 97 was closed over Blewett Pass as firefighters worked to burn dry fuel and take down dead trees.

Starting at 10 a.m. Saturday, Highway 97 will be restricted to one lane both directions due to the  fires getting close. Agencies will be escorting vehicles during the time and if the fire gets closer, the highway will be closed.

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 keep them from stopping," fire spokeswoman Connie Mehmel 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.

The smoke has already prompted some schools to relocate weekend sporting events. Central Washington University has moved its Saturday home game against Azusa Pacific University from the CWU campus to Pop Keeney Stadium in Bothell. 

The Red Cross opened a shelter in North Bend to help Ellensburg area residents affected by the wildfires and subsequent hazardous air conditions. The shelter is located at the Si View Community Center at 400 Southeast Orchard Drive.