BOULDER, Colo.—Colorado firefighters have boxed in the big fire that destroyed nearly 1,000 homes in their effort to prevent it from spreading—but officials warned Tuesday that gusty winds expected ahead of a snowstorm could cause flareups in the burn zone between Denver and Boulder. About 200 firefighters were working to douse smoldering spots in damaged buildings and bone dry vegetation that serves as tinder to fan wildfire flames as the gusty winds descended from the Rocky Mountains. The fire that started last Thursday was finally fully contained on Tuesday by firefighting crews from across Colorado and the blaze burned 9.4 square miles (24.3 square kilometers) in suburban areas and grassland northwest of Denver, said David Boyd, spokesman for an incident management team in charge of the fire’s suppression in Boulder County. Although the blaze died down in recent days and was no longer considered a threat because of a snowstorm …