The monsoons arrived on schedule in northern New Mexico on Monday, bringing with them the promise of containing a monster wildfire that has broken records in the state.

But they also brought potential peril from flash floods, wind bursts and lightning, with possible flooding made worse by the ground-clearing fires.

"It's such a Catch-22 with the rains," said Arlene Perea, a fire information officer. "The rains are welcome, but we know there are some problems with it."

The National Weather Service on Monday put out a flash-flood watch for the fire area through at least Wednesday. Forecasters said showers and thunderstorms were expected, with hail, lightning and winds up to 45 miles per hour.

Last week, Governor Susana Martinez issued an emergency declaration to free up about $700,000 in state funds for flood mitigation efforts across the state.

The Las Conchas blaze, New Mexico's largest wildfire ever, has burned 147,642 acres since June 26 when winds knocked an aspen tree against power lines, igniting the fire in the Jemez Mountains about 12 miles southwest of the city of Los Alamos. As of mid-afternoon Monday, it was 50 percent contained.

At one point, the flames had forced the evacuation of the town of about 12,000 and lapped at the borders of the Los Alamos National Laboratory, the linchpin of American's nuclear weapons industry.

The lab was shuttered for about a week amid concerns about the possible release of radioactive and other hazardous materials. Lab officials later insisted no such releases occurred.

On Monday, forestry officials seemed as hopeful as they have been since the fire began.

"We got a big rain on the fire this morning, and things are really looking good, especially on the north end," Perea said.

That area includes the Santa Clara Indian reservation where firefighters have been battling to save sacred and cultural Pueblo sites, including Chicoma Mountain, regarded as "the center of all" by many tribes.

Containment lines were said to be holding on the three sides of the mountain that were burning.

Perea said firefighters had not been plagued by lightning strikes or high winds, and were being kept out of canyons where rainwaters could flow dangerously unimpeded over scorched earth stripped of ground-hugging vegetation.

On the southern end of the blaze, where little rain had fallen as of Monday afternoon, firefighters also were protecting other Pueblo holy sites and ancestral ruins from both fire and possible flooding, said David Schmitt, a fire information officer.

"They are trying to keep the fire intensity low so it doesn't take out the canopy, which will act as a buffer when the rains do come," Schmitt said.

He said there were several flare-ups Monday and over the weekend, but all were well within the fire's containment lines.

Fire lines also were holding north of Los Alamos and the nearby Pajarito Mountain ski resort.