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HAMILTON – Strong winds and unexpected fire behavior late Tuesday afternoon prompted the Ravalli County Sheriff's Office to begin notifying some residents near Lost Horse Road to prepare for possible evacuation because of the Observation fire.

The Ravalli County Sheriff's Office announced a Stage 1 alert, meaning a high probability of needing to evacuate for Gold Creek, including Whispering Pines and Highland Drive south to U.S. Highway 93 to Lost Horse Road and including both sides of Lost Horse Road.

Law enforcement will attempt to make personal visits to each resident and business living in the affected area.

The fire grew much worse at about 4:30 Tuesday afternoon when it jumped the eastern ridge and ran laterally down the east slope. At that point, all fire crews, more than 110, were pulled off the line because of "extreme fire behavior," the forest service reported.

Meanwhile at least one helicopter was grounded because of high winds during the afternoon. One fire tanker was dousing the flames with fire retardant. Three more air tankers have been ordered.

The fire, in the Bitterroot National Forest, is still estimated at 322 acres, but it's the hot, dry weather, winds and low relative humidity that make the fire conditions extremely dangerous.