Firefighters in Colorado boosted efforts to get a week-long wildfire southwest of Denver under control, encouraged by getting the blaze 30 per cent contained, but worried about unpredictable weather.
The Hayman fire grew slightly to nearly 103,000 acres (41,200 hectares) from 100,000 acres (40,000 hectares). But while the picture had improved, weather and specifically wind remained unpredictable and flare ups could occur.
The fire was 30 per cent contained by late Friday night, a big jump from days of zero or only 5 per cent containment. But later today concerns grew. "The weather today is exactly the way it was the day this fire went 19 miles," US Forest Service spokeswoman Ms Susan Zornek-Stevens said, referring to a big jump the fire took on Sunday.
The fire, about 55 miles (90 km) southwest of Denver, which has not touched the Mile High city, is believed to have been started by an illegal campfire, but federal investigators were still looking into the cause.
Containment does not mean that a fire is extinguished, but rather that a line or break around the fire has been completed. The line can include natural barriers or manually built lines, according to the National Interagency Coordination Center.
Thunderstorms were expected sometime today. While the storms can bring rain they also whip up winds forcing crews to abandon their work.
Colorado, like other Rocky Mountain states, is in the grip of a severe drought, making timber bone dry and vulnerable to either lightning strikes or flying embers from man-made fires left unattended.
State governor Mr Bill Owens has issued an outdoor fire ban throughout the state and no one can sell or set off firecrackers until further notice. Some localities outside the fire region have canceled July 4 Independence Day professional fireworks shows.