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Two Minnesotan firefighters walk back to their truck from the Bacon Rind fire, burning on the Northwestern edge of Yellowstone National Park just west of U.S. Route 191.

Weather is going to be  a concern for fire crews today as a cold front moves through southern Montana. 

The National Weather Service has issued a Red Flag Warning for fire weather for Park and Gallatin counties because of low humidities, high temperatures and variable winds that could cause erratic fire behavior. 

The warning lasts until midnight Friday. 

It will be of particular concern to managers of the Bacon Rind fire, which is burning in the northwestern corner of Yellowstone National Park and the eastern edge of the Lee Metcalf Wilderness. An infrared flyover Thursday night put the blaze's size at 1,929 acres. Of that, 1,088 acres are inside Yellowstone and 841 are in the Lee Metcalf, according to the fire information service InciWeb.

Jeff Gildehaus, a fire spokesman, guessed that the fire — which has been burning moderately for nearly a month — has been growing between 75 and 100 acres per day. 

Recent growth has come on the southern and northern ends. Gildehaus said modeling predicts the fire will grow to the west — farther into the Lee Metcalf — but he stressed that it was just a prediction. 

Crews are trying to keep it from jumping east across U.S. Highway 191 and have been successful so far. Gildehaus said it's been burning moderately and predictably, but Friday's weather could change that. 

A cold front blowing over the area will bring strong and erratic winds. So will coming thunderstorms, which Gildehaus said can create problematic down drafts that blow in different directions. 

"It can be very localized and it can push fire in any direction," he said. 

About 70 firefighters are working on the Bacon Rind fire. A new start across the road, the Terminal fire, burned a third of an acre. Gildehaus said firefighters are still keeping an eye on that one. 

Michael Wright can be reached at mwright@dailychronicle.com or at 582-2638. Follow him on Twitter @mj_wright1.