Firefighters are struggling to get a handle on a large and growing wildfire northeast of Ellensburg just as lightning storms with gusts up to 50 mph are forecast for tonight and Thursday in South-central Washington. Farther south, firefighters made good progress Tuesday on the Mile Marker 28 Fire.

Together, the Colockum Tarps Fire in Chelan and Kittitas counties and the Mile Marker 28 Fire near Satus Pass are estimated to have burned 128 square miles. Smoke from the fires clouded skies over a wide swath of the region, increasing harmful air quality conditions since Monday.

Firefighters on the Colockum Tarps Fire began digging containment lines on the fire’s south side, which had advanced quickly through grass and sage brush. By last report early Tuesday evening, the fire had grown to nearly 60,000 acres, with the potential for growth considered extreme. The fire was estimated to be 8 percent contained.

The fire’s growth prompted the Kittitas County commissioners to declare a state of emergency and its sheriff’s office to issue an evacuation notice for an area near the Columbia River.

Crews had been focused on protecting homes and other structures in Chelan County, where the blaze began Saturday morning. More than 60 homes have been evacuated, and the fire has burned three primary houses and several outbuildings.

But as the fire moved farther south Tuesday in Kittitas Valley, firefighters have also been working to protect power lines, natural resources, a natural gas pipeline, recreation areas and wind farms.

Bulldozers began building containment lines Tuesday to check the fire’s advance to the south, and three elite firefighter crews were transferred from the Mile Marker 28 Fire to help that effort.

In all, about 370 personnel were assigned to the fire as of Tuesday, and more are en route. Helicopters have supported fire crews from the air.

The state Department of Natural Resources is investigating the fire’s cause.

The wind shifted Tuesday, pushing heavy smoke west into the upper Kittitas Valley, where some residents thought the smoke was from new fires.

“We ran on a number of false alarms,” said Russ Hobbs, chief of Kittitas Valley Fire District 7.

Like many firefighters across Central Washington, Hobbs is nervous about current fire conditions. The National Weather Service issued a red flag warning through Thursday in Kittitas, Klickitat, Yakima and Benton counties due to a forecast of lightning storms, wind and heat.

“Our rigs are fueled up and ready to go,” he said.

The weather this year has been hotter and drier than normal, according to Diana Hayden, a National Weather Service meteorologist.

The next couple months are expected to be closer to historic averages, which are still highly conducive to wildfire, she said.

Local firefighters don’t expect a break in August and September, traditionally the busiest months for wildfires in the Lower Valley, according to Brian Vogel, chief of Yakima County Fire District 5.

Conditions are so dry that there’s less humidity in vegetation now than in a sheet of paper sitting on an office desk, Vogel said.

Those conditions helped fuel the Mile Marker 28 Fire around Satus Pass, which has burned 22,469 acres since it began a week ago.

But firefighters have contained the north and south sides, and worked Tuesday on closing the east side of the fire.

Their progress hadn’t been confirmed Tuesday, but fire officials expected to see a “big jump” in how much of the fire has been contained, said Nick Cronquist, a spokesman with the fire management team.

Officials were optimistic enough to start releasing some fire crews, including the three elite hotshot crews. At its peak, the fire had 1,345 personnel assigned. Most are still on hand.

Residents have been allowed back to their homes in areas south of the fire that had been evacuated. According to the Klickitat County Sheriff’s Office, 255 people had been affected by an evacuation notice. Another 647 people were warned at some point that they might need to evacuate.

U.S. Highway 97 has been reopened to residents up to milepost 24 from the south and will be monitored by sheriff’s deputies.

The Bureau of Indian Affairs is investigating the cause of the fire, which began on the Yakama reservation.

Smoke now covers much of South-central Washington. In places, the smoke had reached levels considered harmful. People with lung and heart disease, diabetes or a respiratory infection, people who have had a stroke, infants, children and adults older than 65 are most at risk.