Jason Forthofer had been fighting the Sunrise Fire in southern Montana for more than a week when he made the biggest mistake of his career. He was working with a team at the fire’s edge, digging trenches and lighting controlled “backburn” blazes in the stifling heat, when he heard a rumor about a cabin nearby that might need protection.

Curious and eager to help, Forthofer and his colleague Kevin Beck shouldered their packs early one morning and picked their way up an old mining trail into the nearby forest. Forthofer was on foot, while Beck rode a four-wheeler. Soon they were pushing through thicket, branches snagging the heavy material of their fire-retardant coats. Maybe there were a few clouds overhead; if there were, Forthofer ignored them. The incident meteorologist working with the team had been warning of possible thunderstorms for several days—typical for a Montana summer—but none had materialized.

The cabin, when they found it, was about a half-mile from the road, a rickety mining shack patched together from scrap metal and surrounded by Douglas firs. They surveyed the building: it looked as if people had been there recently, but nobody was home now. Then Forthofer heard a sound that made his stomach drop: the deep rumble of thunder. The tops of the nearby trees began to sway.

Beck jumped on his four-wheeler and Forthofer jogged him, making his way to the road as fast as the thick brush would allow. They’d taken a stupid risk by ignoring the forecasts—and they knew it. An approaching storm could easily kick up dangerous winds, pushing uncontrolled fire toward them at terrible speed.

Forthofer’s panic mounted as the winds increased. Thirty miles an hour. Then 40. As they approached the road, he broke into a run, knowing the flames could reach him at any moment.

Sweating and exhausted, terrified by what could have happened, Forthofer and Beck made it back. They were safe. But one thought played over and over in Forthofer’s mind: I could have died right there. That’s how firefighters die.

Jason Forthofer stands on the roof of the Missoula Fire Sciences Lab. Kristine Paulsen

Sunrise was just one of 21 fires that burned Montana over the summer of 2017. But the blaze was mostly contained by the time Forthofer sat at his desk a few weeks later and considered his experience from a different perspective. When he’s not fighting fires directly, Forthofer studies them, working with a group of analysts, biologists, computer programmers, and engineers at the Missoula Fire Sciences Lab in Montana.

His dual roles—on the front line and as a researcher—exemplify the lab’s unique position in American wildfire fighting.

“That context is critical, and it’s not something that most scientists get,” says ecologist Matt Jolly, one of Forthofer’s colleagues. “They're trying to write about wildfire, write about crown fire [in tree canopies]. And they've never seen one!”

The Fire Lab is perhaps best known for the computer programs it produces to forecast wildfire behavior. In 1972, a researcher named Dick Rothermel used a series of simple experiments to create one of the first mathematical models that could predict how a fire might spread. Burning fuel in its wind tunnel, Rothermel controlled for factors like wind speed and then observed his fires as they grew. He plotted the results on a graph and used the data to deduce a set of equations that could be applied to wildfires everywhere. Suddenly, analysts could make predictions about the way a blaze would spread—and the results changed the way experts think about and interact with fire.

Matt Jolly watches a fire burn in the lab. Kristine Paulsen

Today, the Rothermel model provides the spine for almost every computer program used to analyze wildfire behavior in the US. But although his work was advanced for its time, Rothermel didn’t take into account many of the factors that make fires behave differently in the real world than they do in the limited environment of a lab. His research assumed, for example, that pine needles in a shallow fuel bed would burn the same way as the same needles stacked much higher. Models like Rothermel’s are “only really valid for the range of data and experiments you ran,” says Forthofer. “Outside of that range, it's anybody's guess whether the curve keeps going.”

To compensate, fire behavior analysts have been bolting an almost endless series of adjustments and inputs onto Rothermel’s skeleton so that they can make more accurate predictions about how a particular blaze will progress over the course of hours or days. They incorporate data describing everything from slope to vegetation to canopy characteristics and weather factors. The whole thing is a feat of technology and ingenuity, an attempt to predict something that has been spent centuries being mysterious and unknowable.

Today, though, after decades of drought and rising temperatures, monstrous blazes throughout the American West have brought the system’s weaknesses into focus. Rothermel’s model can’t deal with everything the environment is throwing at it, from the number of dead trees now standing in America’s forests to fluctuating wind speeds.

A portrait of Harry T. Gisborne, forest fire research pioneer, greets visitors as they enter the Lab. Kristine Paulsen

“The tools are not always right,” Forthofer explains. “They’re almost never right, never perfectly right.” And when they’re wrong, it can lead to real and serious consequences: lost money, lost homes, or—worst of all—lost lives.

So, with infernos eating through tens of thousands of hectares and killing more people each year, the Fire Lab is trying to build a brand new model for the first time in half a century. There’s a lot of catching up to do.

One afternoon in July 2019, Forthofer gives me a tour of the lab, accompanied by his boss, Mark Finney. Firefighting is never far away for Forthofer—his brother and wife were both firefighters, and many of his friends still are—and he has the solid physique of someone who regularly hikes with 100-pound packs. Finney, by contrast, is wiry and angular, with silvering temples and a tendency to speak in short bursts.

Starting in the building’s foyer, idiosyncratic touches abound. A stuffed mountain goat presides over the front desk area (“Please do not touch the goat,” pleads a nearby sign). A wildfire-themed patchwork quilt from 2010 commemorates the lab’s 50th anniversary.

Outside, clouds race across the plains, but you wouldn’t know it inside the cavernous, windowless space of the test laboratory, whose towering internal walls are made of corrugated metal. We stop in front of a hulking slab filled with sand, which Forthofer and Finney explain is essentially a giant burner. They point out the custom propane jets underneath, which allow them to precisely control the intensity of the flames and take exact measurements as they burn.

The lab has nicknamed the table “Big Sandy,” Finney tells me. (They’ve christened similar burners “Little Sandy” and “Big Bertha.”) One of Big Sandy’s signature experiments measures flame length, temperature, and pressure in a fire that starts in a straight line. Rows of laser-cut cardboard tines burn up one by one in an almost liquid movement as a line of flames as high as 8 feet tall spreads across them, forming a wave of peaks and troughs.

Measurements on Big Sandy have shown that these shapes are caused by cold air pushing the flames intermittently down into their fuel bed, driving the combustion process. A video recording put through a “flow trace” analysis adds thin green lines that make it easier to track that movement. It shows how this cold air spins into a series of small whirls, or vortices, when the gases in front of the flames rise and fall as they heat and cool. Without that movement, flames wouldn’t move forward, Finney explains; they’d simply float above their fuel and eventually go out.

In an office down the hall from Big Sandy, fire analyst Chuck McHugh takes me through some of his work. The models he shows me from past wildfires look like tangles of red squiggles and colored blotches overlaid on maps. In fact, he explains, the red lines document possible paths that the fire might take; the colorful shapes indicate the number of hours the fire might take to spread to that area. On some of the maps, these blobs are surrounded by bubbly spot fires, “ignitions” where the software guessed that sparks might leap away from the main blaze. The whole thing resembles a slime mold, organic and alive—which, in a way, it is.

Everywhere we walk, the team is trying to better understand and predict fire behavior. Upstairs are the wind tunnels, where Forthofer and his colleagues record how fires are affected by air at different speeds. He also shows off a tall, black metal apparatus whose curved base generates the airflow necessary to create (and study) 10-foot fire tornados. We finish our tour in a room full of foam-and-metal contraptions for measuring how heat moves through the air to ignite new fuel as a fire starts The whole place, they explain, can be set to a specific air temperature and humidity or opened for ventilation in case of emergency.

Finney says all this complexity shows that Rothermel’s work just isn’t enough anymore.

Mark Finney stands in front of “Little Bertha,” a piece of equipment which allows scientists to test how fire moves up a slope. Kristine Paulsen

“Just because you have a model,” he says, “doesn’t mean you understand something.”

Wildfire is full of small-scale processes like Big Sandy’s vortices. Each piece of the research the Fire Lab undertakes is an attempt to study a tiny part of the big picture. And it’s particularly important with elements like wind, which both affects how fire behaves and goes on to be affected by fire. The Rothermel model, Finney argues, comes nowhere close to accounting for the feedback loops and strange behavior thresholds in a complex system like that.