Three days after a wind-whipped blaze claimed the lives of 19 "hotshot" firefighters near Yarnell, Ariz., investigators have begun the grim work of establishing how nature and chance could have gotten the better of a team of the fire service's best.

"What I can tell you is that our hotshot crews are some of our most elite firefighters. They were trained for almost anything," said Bequi Livingston, an 18-year veteran of the hotshots who now works as a fire operations health and safety specialist with the Forest Service's Southwest Region.

A Serious Accident Investigation Team has been dispatched to learn the facts of the accident, she said. Its findings will likely take several days, and possibly much longer, to be finalized.

What is known, however, is that conditions in the region were primed for ignition when lightning touched off the blaze late Friday afternoon. The fire burned steadily until Sunday, when it exploded to encompass some 2,000 acres amid triple-digit temperatures and powerful winds.

The flames spread quickly through the tinder-dry grasslands and chaparral that lie to the west of Yarnell, breaching the small town's limits and destroying more than 200 structures. Fire officials said that the 19-member hotshot team -- a 20th member was elsewhere and remains unhurt -- were maintaining one flank of the fire line when the wind abruptly changed direction and drove the fire back toward them.

A number of the crew deployed fire-resistant personal structures, a last line of defense when escape routes have been cut off. Helicopter support attempted to reach the stranded crew but was driven back by the fire.

The loss of the 19 young men has been called the worst wildland fire disaster in 60 years and is the largest single loss of life among firefighters since the Sept. 11, 2001, terrorist attacks.

Nature plays a wild card
Hotshot fire crews are among the most highly trained of all firefighters and are held to the profession's highest physical standards. Fire officials often offer analogies to Army Rangers and Navy SEALs -- small, coordinated groups of specialists trained to bring force to bear wherever it may be needed. Hotshot crews can complement federal, state or local agencies, Livingston said.

The 19 belonged to a division known as the Granite Mountain Hotshots and were members of the city fire department of Prescott, Ariz.

Yet even a highly trained crew can be overwhelmed by a "perfect storm" of meteorological conditions, experts said. And many of those conditions were in play in the days leading up to Sunday's disaster.

Like much of the Southwest, Arizona has been under protracted drought conditions for more than two years. Much of the state is currently under "severe" drought warning, while pockets of extreme drought hang in the east and central regions, according to U.S. Drought Monitor maps.

In a map updated June 25, the Drought Monitor shows one such pocket of extreme dryness hanging directly over Yavapai County, home to the town of Yarnell.

Hot, dry weather exacerbates fire potential by sucking moisture from the landscape. Already a historically arid part of the country, Yavapai County has seen about 50 percent of its expected precipitation over the past seven months, said Brian Klimowski, head meteorologist at the Flagstaff, Ariz., office of the National Weather Service.

But such arid climates can have another effect on fire conditions, one potentially more concerning to firefighters.

"When you have an area that's this hot and dry, and you introduce a little moisture in the form of precipitation, you're going to immediately see a lot of evaporation, and evaporation from rainfall causes cold air to be produced," said Klimowski. "Cold air is buoyant, dense -- it falls to the ground, rushes out, spreads. That's the origin of the strong winds you get preceding thunderstorms."

There were a number of thunderstorms surrounding the Yarnell fire on Sunday. And while meteorologists don't have complete data to determine the origin of the winds, observations from the site are consistent with the kinds of strong, gusty, erratic winds one would associate with multiple storm fronts, Klimowski said.

Yarnell sits in a corner of the Peeples Valley, bounded on three sides by mountains. That complex terrain likely helped funnel the winds in changing directions, said Chuck Maxwell, a predictive services meteorologist with the Southwest Coordination Center.

"What you ended up with was maximum potential for chaos," Maxwell said.

An eye on the sky for the boots on the ground
Those conditions persisted through Monday and only slackened slightly Tuesday with the arrival of slightly cooler temperatures and light precipitation.

The ongoing severe weather has kept many fire crews at bay, though most of the wildland firefighters in Arizona have by this point been deployed to the site. Federal firefighting agencies were poised to take over management of operations Tuesday evening, shortly after the national fire preparedness level rose from 2 to 3.

At preparedness level 3, multiple geographic regions require significant support from federal resources. The highest level is 5, reached only during the most severe wildfire years.

In addition to the boots on the ground, areal and logistical support, the federal government often provides incident meteorologists (IMETs) to fire teams operating on-site. These IMETs are embedded in National Weather Service offices around the country and are deployed at the request of firefighting command posts once a post has been established.

Because the Yarnell Hill fire moved so quickly, command posts were still being established when the 19 hotshots' position was overrun, Maxwell said.

Speaking during a tour of the operations floor of the National Oceanic and Atmospheric Administration's Center for Weather and Climate yesterday, acting NOAA Administrator Kathryn Sullivan said that hotshot crews are often chief candidates for IMET support.

"Not to be overly speculative, but typically, we would have our IMET embedded with the kind of hotshot crew that was overrun by fire on Sunday," she said. "That kind of extremely rapid wind shift that turned the fire against them, that's just the kind of impending hazard, rapid, fast-moving hazard, that the IMETs try to protect the firefighters from."

Stephanie Paige Ogburn contributed to this report.

Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC., 202-628-6500