CLINTS WELL, Ariz. — A wildfire in Arizona grew but improved weather conditions Tuesday could help firefighters in the area with numerous summer and vacation homes, officials said Tuesday.

Higher humidity and cloud cover should help nearly 600 personnel assigned to the fire that has grown to nearly 18 square miles (46 square kilometers) south of Flagstaff, fire management team spokesman Brian Scott said.

Firefighters were trying to keep the blaze from burning toward housing tracts or into a valley where it could burn for a long time, Scott said.

Officials have estimated that the fire about 50 miles (80 kilometers) south of Flagstaff has burned 30 buildings and threatened about 1,000 homes and other buildings.

The fire is under investigation but believed to be caused by a human.

Separately, forecasters said the Southwest U.S. faces significant wildfire danger this summer because of drought and thick stands of grass left over from last year.

The National Interagency Fire Center said the danger of significant fires will be above normal in Southern California through the end of August.

Parts of Arizona, Colorado, New Mexico, Nevada and Utah are at greater risk through June.

By July, the danger will increase in the Pacific Northwest.

The forecast says most of the rest of the country will face normal or below-normal risk of major fires this summer, including the Southern Plains, where drought and fires hit farmers and ranchers in April.