Firefighters had a narrowing window to battle the wildfires raging in the Texas Panhandle on Thursday, as forecasters were expecting higher wind speeds and hotter, dryer air to return over the weekend.

The largest fire, called the Smokehouse Creek fire, was far from under control Wednesday evening, with about 3 percent of it contained. At 850,000 acres, its size had more than quadrupled in a day and was nearing the record for largest fire recorded in Texas, the Texas A&M Forest Service said.

Firefighters have been deployed to the region from throughout the state, including from as far as Lubbock and Fort Worth, under Gov. Greg Abbott’s disaster declaration on Tuesday.

“They’ve got a short window to try to get a handle on it before the winds ramp up again,” said Edward Andrade, the lead forecaster at the National Weather Service office in Amarillo.

Forecasters said that firefighters could be aided on Thursday by weaker winds and cooler temperatures, which were expected to hover in the 30s and 40s, Mr. Andrade said. There was a slight chance of light rain or snow, though he said it would not be enough to dampen the fires.

But on Saturday, strong winds, around 30 miles per hour, were forecast to return, and temperatures were expected to rise back to the 70s. Such conditions, which were likely to continue on Sunday, could accelerate the fire’s spread and hinder firefighting efforts, he said.

“It’s possible that the Smokehouse Creek fire complex may become the largest fire in the state,” Mr. Andrade said in an interview, adding that the current record was held by a wildfire that started east of Amarillo in 2006 and grew to about 907,000 acres.

The rugged terrain of the Canadian River Valley, where the fire started, was another major obstacle for firefighters because there were cliffs, valleys, and steep hills where fire trucks could not get to, he said.

On Tuesday night, the blaze briefly forced the evacuation of the Pantex power plant, a government facility that assembles and disassembles nuclear weapons. Operations at the plant returned to normal on Wednesday, according to Pantex. “There is no imminent wildfire threat to the plant at this time,” Pantex wrote on social media.

The Smokehouse Creek fire, combined with other nearby fires, spanned at least 11 counties early Thursday, in land often used for farming and cattle ranching, Mr. Andrade said. In the town of Canadian in Hemphill County, fires destroyed or damaged dozens of homes.

Texas A&M Forest Service said in its forecasts that the Texas Panhandle’s fire danger rating would rise to “very high” on Friday and Saturday, from “high” on Thursday.

Mr. Andrade urged residents to be cautious. “We ask that people please practice fire safety prevention in order to prevent starting any more fires,” he said.