The Las Conchas wildfire, which for much of the week has threatened the Los Alamos National Laboratory and its namesake city, has become the single largest forest fire on record for the state of New Mexico.

By 4 a.m. Friday morning, the fire had consumed at least 103,842 acres, eclipsing the previous record set in 2003, when the Dry Lakes fire torched 94,000 acres in the Gila National Forest.

The fire has remained at 3 percent contained for several days – highlighting the widespread availability of unusually dry fuels that have allowed the fire to spread quickly even as firefighters race to keep up.

Still, fire officials are cautiously optimistic that the containment figure will rise over the next few days. One reason: Most of the fire's advance in the past 24 hours has been to the north, toward fire scars left from blazes in 1998 and 2010.

Firefighters are trying to tie their containment lines into those burn scars to halt the fire's northward progress, says Jerome McDonald, operational section chief for the Southwest Area Incident Management Team, an interagency task force overseeing the firefighting effort.

In addition, smoke conditions have eased enough to allow tanker aircraft to begin dropping fire retardants on the burn scars left by the 48,000-acre Cerro Grande fire, which struck the city and lab in 2000.

On Thursday, officials reported that the Las Conchas fire was burning so hot that it was reigniting charred tree trunks from the 2000 blaze – as well as grasses and shrubs that had recolonized the burn area – as portions of the fire front encountered the western boundary of the 2000 fire zone.

With help from the aerial tankers, fire officials say they hope to finally turn the Cerro Grance burn scar into a more-dependable barrier protecting land to the north and west of Los Alamos.

So far, the lab and city have gone unscathed, except for a one-acre patch of land on the 23,000-acre laboratory grounds. That small patch caught fire on Monday, a spot fire that was quickly extinguished.

"The lab's safe," says Los Alamos fire chief Douglas Tucker. "All the fire's been kept off the lab, except that one little acre."

Backfires have established what he calls anchors – wide paths of pretorched land that serve as a barrier against the forest fire's advance – that cover much of the rest of Los Alamos County, including the city itself.

Overnight Wednesday night, the Las Conchas fire moved into the watershed supporting the Santa Clara Pueblo, one of 19 native American pueblos scattered throughout the region around Santa Fe and Los Alamos.

Indeed, while the fire has yet to be contained, emergency managers for Los Alamos already are looking ahead to see what measures might need to be taken to reduce the city's and the lab's risk from floods when the monsoon season brings badly needed rain to the region, according to Police Chief Wayne Torpy.

The North American Monsoon brings pulses of thunderstorms to Arizona and New Mexico in July and August.

The concern: Cloudbursts would be delivering intense downpours to mountainsides and sloping canyons denuded of the vegetation needed to hold the water back.

The record size of the Las Conchas fire speaks to the severity of this year's fire season in the Southwest.

As of June 12, the latest tally produced by the National Interagency Fire Center in Boise, Idaho, some 4.12 million acres of forests and grasslands have burned throughout the United States this year. The torched trio of Arizona, New Mexico, and Texas accounted for about 75 percent of the total. Texas saw 1.59 million acres go up in smoke, followed by Arizona with 680,000 acres, and New Mexico with 631,000 acres.

But the Interagency Fire Center's numbers do not include the Las Conchas fire or the Donaldson fire, which erupted in rugged grasslands west of Roswell, N.M., on June 28. The Donaldson fire has scorched more than 72,000 acres.