FORT COLLINS | Firefighters battling a 640-acre wildfire in northern Colorado are concerned about forecasts for thunderstorms and 50 mph wind gusts.

Forecasters also issued a red flag fire warning Wednesday for the eastern plains.

Fire officials said Tuesday that the blaze northwest of Fort Collins was caused by humans and the investigation is continuing.

Calls were made to 160 phones telling residents to prepare to leave, just in case. The fire is within a quarter mile of some homes.

In western Colorado, firefighters expected to have a 170-acre fire between Delta and Whitewater fully contained sometime Friday. It was 80 percent contained Tuesday. That fire was started by lightning. No structures are threatened.