WENATCHEE — A growing force of firefighters, more than 300 strong, prepared this morning to face Swakane Canyon fire, expected to be fueled this afternoon by wind gusts of up 55 mph.

Firefighting crews from across the state and Northwest continued to arrive this morning to help battle the three-day-old blaze, estimated at 5,700 acres and moving rapidly across grass-covered hillsides and rocky ridges.

“These strong winds can be erratic and unpredictable,” said Karen Ripley, spokeswoman for the Washington Interagency Incident Management Team that is in charge of the fire. “We’re building fire lines, bringing in personnel and discussing (firefighting) strategies.”

The National Weather Service has issued a warning for firefighting crews to be aware of the extremely flammable conditions of grasses and brush due to high winds and low relative humidities.

Evacuation alerts remained in effect this morning for all residents of Swakane Canyon and nearby houses along Highway 97A. So far, no homes had been burned and one structure — a barn — charred by the fire.

On Sunday, billowing smoke briefly forced closure of Highway 97A around 5:30 p.m. More intermittent closures of were expected today as winds picked up and the fire finds new fuels, Ripley said.

By Sunday evening, wind conditions allowed firefighting crews to set back fires on Burch Mountain, effectively burning and removing high-potential fuel between Burch Mountain Road and Swakane Canyon, Ripley said. “The conditions were right to do this confidently,” she said, “and we had good results.”

The back-burning resulted in larger blackened areas on Burch Mountain’s southern face, she said, which Wenatchee residents may have spotted from the valley floor.

Overnight, the fire spread northeast to Tenas George Canyon, an east-west draw that runs from a ridge down to Highway 97A, north of Turtle Rock Estates. The blaze was moving through dried grasses and low brush, Ripley said.

By 10 a.m. today, hard figures on the fire’s size and boundaries had not been established, Ripley added. On Sunday evening, the incident management team reported the blaze had scorched 5,700 acres. “But we know it’s grown substantially since then,” Ripley said. Fire teams were expected to take GPS readings on the size of the fire later today.

Today’s predicted high winds would likely have major effects on any wildfires burning today, said Ellie Kelch, a forecaster for the National Weather Service in Spokane.

A cold front bearing minimal precipitation is expected to sweep through the Wenatchee Valley beginning at noon today, Kelch said. “The main factor will be high winds as the front’s cooler air rolls down the Cascades’ slopes and gaps.”

That air will pick up speed as it rushes eastward, she said. Today’s sustained winds are predicted to be 25 to 30 mph, Kelch said, with intermittent gusts of 40 to 45 mph. Infrequent gusts could reach 55 mph, she said. Peak winds are expected between 1 and 6 p.m. this evening.

“These aren’t dangerous, property-damaging winds,” she said, “but they’ll definitely blow over trash cans and, much more seriously, affect firefighting efforts.”

Last night, the NWS issued a warning for the region that included alerts for the dryness of grasses and brush and the potential for blowing dust on the Waterville Plateau and Columbia Basin.

Fire officials Sunday afternoon had put residents living along Highway 97A near the mouth of Swakane Canyon on Level 1 alert, meaning they should be aware of the fire.

It also meant that people living there who have health conditions should have plans in place if they need to evacuate, and people with livestock should be looking for places to place their animals.

Evacuees forced from their homes by the Swakane fire found refuge Saturday and Sunday at the Wenatchee Seventh-day Adventist Church in Wenatchee, at a shelter set up by local Red Cross volunteers.

The 15 people staying overnight at the shelter dined on pizza donated by Little Caesar’s. Pets were sheltered by the Humane Society.

Another 26 homes in Turtle Rock Estates, between Highway 97A and the Columbia River, and 10 homes along the highway were also on Level 1 alert Sunday afternoon.

Keeping the fire from topping Burch Mountain had been a high priority for firefighters, Ripley said, to protect the Sunnyslope area and its many homes.

The Swakane Canyon Road is open to local traffic only, she said. Officials have also closed two roads where the blacktop ends: Burch Mountain Road and the Nahahum Canyon Road.

Mike Irwin: 665-1179

irwin@wenatcheeworld.com