Some chew tobacco. Some sip coffee from Styrofoam cups. A few hack dry coughs. The group is worn thin. For the past 22 days, many have worked 16-hour shifts fighting a group of wildfires outside Chelan, a 4,000-person town. As of that morning, 500 square miles of Washington are burning. “It’s another critical weather event,” Ruthford says into a microphone. A National Weather Service meteorologist, Ruthford’s responsible for a daily morning briefing, with a detailed forecast for the wildfires known as the Chelan complex. Smoke has socked in camp, and she’s issued a Red Flag Warning signifying dry and unstable conditions, ideal for the rapid spread of fire. “Expect the winds to get squirrely in here along the bend,” Ruthford says. She runs a finger along the ridges by a lake on the camp’s map. “Winds will start shifting from the south to the northwest after 15:00.” Ruthford’s stooped shoulders and dour expression match the camp’s mood. She has been forecasting weather for this fire for two weeks and knows what the blaze can do. One day, it sent 200-foot flames shooting through lodgepole and whitebark pine trees beneath alpine glaciers, where fires burn only every 300 to 500 years. Another day, lightning lit off a handful of new blazes around Lake Chelan, and 56,000 acres blackened in 24 hours. The strong winds she’s forecasting, up to 30 miles per hour, will breathe life back into even smoldering embers. “Be very careful out there today,” Ruthford says.

II.

Weather determines how dangerous a fire becomes. Flames can move almost as fast as the wind, and extreme heat often creates bizarre effects. During Wisconsin’s Peshtigo fire of 1871, for example, a cold front and twisting winds combined to form a fire tornado. That blaze killed 1,500 people. It burned so hot, silica in the soil evaporated. When the thunderheads rained, the mineral fell in molten form. Survivors found birds—suffocated midflight by the fire’s insatiable appetite for oxygen—encased in glass. For the Chelan complex, it’s Stewart Turner’s job as a fire-behavior analyst to predict how flames will spread. “The topography and fuel conditions are constants for us,” Turner says. “The only thing that changes is the weather.” That’s why Turner relies on incident meteorologists (IMETs). Ruthford’s one of just 83 IMETs nationwide. Each holds a full-time forecasting job for local weather offices, but they’re also on call for any disaster. IMETs forecasted Hurricane Katrina and Hurricane Sandy as they unfolded, as well as aftermath of the Deepwater Horizon oil spill. But most often, they’re on wildfires. When working on something like the Chelan complex, Ruthford will churn out two daily forecasts, plus a long-term outlook, for an area as large as 50 square miles or as small as a stadium. Over a typical 16-hour shift, she might radio fire crews detailed changes in winds, speak at community meetings, or create forecasts for specific locations, such as a particular ridge on a fire line. IMETs don’t tactically plan how a fire will be fought. That’s left to the firefighters, who may dismiss, overlook, or simply not receive weather forecasts, sometimes with disastrous consequences. In 1994, 14 elite firefighters died when they were surprised by a cold front that caused Colorado’s South Canyon fire to detonate near Glenwood Springs. Two years ago, on Arizona’s Yarnell Hill fire, sudden 50-mile-per-hour winds left 19 firefighters dead when they were trapped by a wall of fire moving toward a town. Those tragedies struck despite advanced warnings. Today, firefighters are paying ever more attention to meteorologists. IMETs have been deployed 150 times this year and, at one point, 44 were deployed at once—a new record. But that increase has as much to do with the changing face of the American West as it does enhanced caution. Some 140 million Americans now live in places that were once wilderness and are still fire-prone. Keeping homes and people safe from the 70,000 wildfires each year demands that firefighters use all the tools available. Money is one of them. The U.S. Forest Service, the country’s largest firefighting agency, has already spent $1.4 billion sending crews, planes, and heavy machinery into the backcountry to quell flames this summer. Despite that, more than 8.9 million acres have blackened, mostly in Alaska, California, and the Pacific Northwest. By year’s end, it’s expected that wildfires will burn almost 10 million acres and 3,000 homes, putting 2015 on pace to be the worst fire season on record. IMETs are another important tool. Ruthford was at home in Anchorage when she got the call for the Chelan complex. Just a few days later she was lakeside at the Washington campground, scrambling to put together a forecast while flames rolled toward million-dollar Swiss-style chalets in town.

III.

After the morning briefing, Ruthford returns to the grass-floored yurt where she predicts the complex interplay of wind, temperature, and barometric pressure. It’s lit with floodlights, and infrared maps of the Chelan complex are pinned to the walls. There are no thermometers or barometers. Unlike firefighters, who rely on tools they can carry in their hands, Ruthford relies on weather models and her laptop. She hunches over her computer, clicking through satellite imagery that shows water vapor rotating over the Northwest, surface temperatures along the Columbia River, and a wind map textured with moving barbs. She compares the way air sweeps over a landscape to the way water flows in a river, varying in speed and density based on topographical features. Pressure lines stream together and apart as she watches them move over mountains in a digital model. Ruthford builds forecasts by stitching together a multitude of data points. Those include information gathered by the country’s 123 weather-service offices, but their forecasts, accurate down to half a square mile, can’t account for every nuance in terrain. So Ruthford needs local data as well. Remote Automated Weather Stations (RAWS) provide real-time updates on the fire area. She also scouts the terrain by helicopter, and every few days releases a weather balloon the size of a van to collect data above the fire. The models are hard to manage. “All day, every day, I’m comparing what’s happening now to what I thought was going to happen, and using the difference to tweak my forecasts for tomorrow,” she says. Ruthford prides herself on accuracy. She’s been working fires since 2003, when she was sent to a blaze 40 miles north of Chelan. During one shift, Ruthford drove out to a nearby canyon on the Thirtymile fire scar, where wind-whipped flames had killed four firefighters two years previously. Standing there convinced her she had found her calling. She had been drawn to meteorology because she wanted to find “the best spots to windsurf, ski, or kayak.” But she stuck with it because of fire. “I first got into this job to play better,” she says. “Now it’s about protecting people.” Since then, she’s spent a month each year in fire camps. In the yurt, Ruthford opens three tabs that show barometric-pressure measurements. Some days, she draws a map to visualize the pressure gradient—the greater the difference, the stronger the winds. But today, she doesn’t need to. The numbers look the same. A temperature inversion has trapped a layer of hot air over the blaze, like it has for the past week. But west of the Cascades, she sees something concerning. A band of salty marine air is blowing east off the Pacific and piling onto the 10,000-foot mountains. Ruthford’s latest models tell her that around 2:00 p.m., when the air becomes deeper than the peaks are tall, it’ll be forced southeast down Lake Chelan, building wind speeds up to 30 miles per hour. Nature’s bellows—the reason she warned firefighters at the morning briefing. The winds will fan the flames. Powerful smoke columns will punch through the inversion, and the energy stored beneath it will erupt skyward. “It’s like a lid boiled off a pot,” Ruthford says. Oxygen will pour into the fire through these smoke-made holes and create its own dangerous winds. Ruthford recognizes the pattern. It’s eerily similar to the storms that caused the deaths at Thirtymile.

IV.

A few hours later, Ruthford squeezes into the backseat of a Forest Service Chevy Tahoe. Joseph Flores, a fire-behavior analyst in training, drives. Turner rides shotgun. Ruthford often works with the smoke-distribution forecasters and fire-behavior analysts who inform tactical decisions at fire camp. They’re heading to a ridge above Lake Chelan, where firefighters and bulldozers have built a fire line to keep flames out of town. Ruthford wants to see how the fire reacts to the weather she predicted in order to refine future forecasts. The Tahoe, like almost everything in Washington state, smells of wood smoke. Occasionally, the radio pops and chatters: Somewhere on the blaze, a firefighter is worried about the threat to a cluster of about 600 homes. Just three minutes from camp, wreckage surrounds the SUV. Wisps of smoke float up in all directions. Flores drives through a smoldering town to a ridge, where a house has been reduced to a grid of concrete slabs. The blackened remains of fruit-storage warehouses sit across the street. A still-smoking oak offers partial shade to the skeleton of a sedan. As they drive by a burned-out home on the lakeshore, Ruthford says, “The last time I saw that house over there, it was standing.” “Winds aren’t materializing, huh Julia?” Turner asks her from the front seat. The inversion is keeping the lid on the pot, trapping smoke over the lake like a thin fog. Over the past decade, Turner and Ruthford have worked together on a handful of fires from Alaska to Arizona, and he likes giving her a hard time. “No, Stewart. They haven’t,” she says dryly. A helicopter dips a 250-gallon bucket into Lake Chelan, then drenches flames creeping toward a burned vacation home. After an hour’s drive on dirt roads so hammered by trucks that the dust covering them is fine and slippery, they stop at the fire line above the lake. Firefighters nearby ignite the forest with drip torches, metal canisters filled with diesel and gas that spread liquid flames. Setting small, strategic fires can deprive bigger blazes of fuel, stopping their advance. So far, the operation is going perfectly. The crews are hoping to blacken a mile of ridge before nightfall. Nobody seems overly concerned about the weather. Ruthford snaps a picture of a drip torch on the ground. “I don’t get to see these very often,” she says. They’re usually in use. Dust starts to swirl behind her in eddies. The marine air finally pushes through. The effect is instantaneous. From behind a ridge a half-mile away, there’s a whoosh as pines ignite. Black smoke boils upward. Flames run toward different fire lines, which hold. In moments, the smoke is 15,000 feet high and curdling into bleached cumulus clouds. “That’s the instability!” Ruthford says, as the smoke column expands skyward. The air over Lake Chelan clears, and in the distance, three more smoke towers punch into the atmosphere. Ruthford, pleased with the accuracy of her forecast, turns back to the truck. She’s inside and driving away before a column from a new fire outside the nearby town of Twisp begins to rise.

V.

The smoke will eventually blow all the way to Chicago, but it’s just starting to bend over the fire camp by the time Ruthford returns. The winds are still strong, howling up the Columbia River. They roll great clouds of dust between the yurts. The afternoon light is tinted orange. Solemn-looking firefighters stand in small groups, talking quietly. The new fire outside Twisp has turned deadly. “How many can we afford to send?” someone asks. Eventually, everyone is called into a large central yurt. Shortly after the new blaze began, flames spread toward town. Helicopters, firefighters, and engines were pulled off the Chelan complex and neighboring fires, and sent 50 miles away to the new blaze. One was Engine 642 from the Forest Service’s Methow Valley Ranger District. When the winds reached the ridge outside Chelan, they also blew over the new fire, as Ruthford predicted. An hour later, firefighters found Engine 642’s crew about 40 feet below Woods Canyon Road. Inside were the burned bodies of 20-year-old Tom Zbyszewski, 26-year-old Andrew Zajac, and 31-year-old Richard Wheeler. Outside, 25-year-old Daniel Lyon lay in white ash, critically burned. News of the deaths hit Ruthford and the Chelan complex’s fire camp like a gut punch. The firefighters disperse from the meeting. Some head to dinner, because what else is there to do? Others linger in the avenue and cry. Some go to the docks to be alone. Ruthford heads for her desk. Her face is pulled tight like she’s nauseous. Todd Gregory, a fire-behavior analyst, comes over, gently tapping the forecasts piled before her. “It’s not your fault. You don’t make the weather,” Gregory says, “you just predict it.” Gregory leaves, and Ruthford remains in the yurt alone. For a long time, she just sits. Then she sighs and opens her laptop. She has a morning forecast to produce, and tomorrow’s weather looks worse. This article was originally published in the November 2015 issue of Popular Science, under the title “On Fire.”