When the Ptarmigan Fire ignited Monday afternoon in the White River National Forest, the weather seemed good for firefighting. Temperatures were cool, even dipping below 50 degrees come evening. Rain was in the forecast the next few days, making the air humid, at least by Colorado standards.

Yet overnight, the fire grew from 17 to 60 acres. Despite rainfall, the fire kept expanding—according to forest service officials, it had covered 85 acres as of Thursday morning. While that may seem diminutive compared to the Cameron Peak Fire, which burned 208,913 acres total in 2020, the Ptarmigan Fire nevertheless created a scary situation for those living in nearby Silverthorne. According to the Summit County sheriff, 183 residences were evacuated Monday and Tuesday night, with many more under pre-evacuation order.

The fire’s unpredictable behavior drove official’s decision to order the evacuations. Even though the damp conditions in Summit County this week would usually result in a less extreme, slow-spreading flames, the Ptarmigan Fire easily incinerated the area’s drought-ravaged lodgepole pine and spruce—making it difficult to forecast how quickly it could spread to neighborhoods in Silverthorne. “It’s taken years for it to get this dry,” says David Boyd, a public affairs officer for the White River National Forest. “A couple days of rain isn’t going to be enough to extinguish the fire.”

All that dry fuel filling forests across Colorado and the West means the Ptarmigan Fire’s erratic behavior is becoming increasingly common, says Boyd. Dan Dallas, incident commander for the Rocky Mountain Type 1 Incident Management Team, agrees. “We have all these models that we depend on when we’re out there,” he says. “But they’re getting less and less dependable, because they were made before fires reacted like they do now.” And when the most predictable thing about a wildfire is that it’s going to be unpredictable, putting it out becomes a perilous proposition.

Dallas joined the incident management team about 30 years ago. Back then, he says, if he fought flames 30 days of the year, it was considered a busy fire season. These days, 80 days or more is the norm. Dallas has overseen efforts to extinguish some of the West’s most devastating wildfires, including both the Cameron Peak and Pine Gulch infernos last year.

That means Dallas knows firsthand how fire behavior has changed. “It used to be common knowledge that a fire couldn’t jump over the Continental Divide,” he says. Then last year’s East Troublesome Fire did just that via a process called spotting, in which a column of smoke carries active embers and burning debris high into the atmosphere. There, it’s sucked into a jet stream or another draft that carries it sideways. Eventually, the flaming material falls into another location, and if conditions are right, causes another fire—and an extra battle for crews.

Keeping an eye out for spotting and extinguishing burning deposits before they grow has gotten harder in recent years. “We have someone called a fire behavior analyst on our team who will forecast spotting potential,” Dallas says. “The area used to be fairly short, maybe a quarter of a mile or so. Now, the fuel is so dry, we’ve seen spotting happen six miles out.”

The Ptarmigan Fire exemplifies another alarming change. Summit County’s cool, humid weather would once have caused the fire to “lay down,” Dallas says. Instead of sweeping through the landscape, flames would grow smaller and largely stay put, almost mimicking the calm of a dying campfire. Crews used that lull, which often occurred at night, to prepare defenses, digging a line of exposed soil to act as a barrier between the advancing flames and unburnt forest, as well as burning away downed trees and other tinder to remove fuel from the fire. Now, though, fuels are so dry that the fire moves shockingly fast.

“We’re either forced to depend upon a barrier already in place, such as a road, or dig a line many more acres from the fire to give us time to get it done,” Dallas says. “Otherwise, I’m putting my people in danger.” The result is more acres burned, even though planes and drones drop flame retardants to try and slow the blaze. Sometimes, flames move so quickly that fire crews can only focus on evacuating nearby civilians, instead of stamping out the inferno.

Luckily for Silverthorne residents, the humidity gave way to several days of rain this week—not just a drizzle, which Dallas says often doesn’t even reach the ground, but a “wetting rain” that eventually provided enough moisture to dampen the fuel and slow the Ptarmigan Fire. Summit County sheriff Jaime FitzSimons announced Thursday morning that evacuees could return to their homes, though they still need to be ready to re-evacuate. (Civilians can keep an eye on the Ptarmigan Fire here.)

But Dallas emphasizes that the disruption caused by Ptarmigan Fire is only going to get more common. “When we don’t know how a fire will act, we grow more cautious,” he says. “It’s the best way to keep people safe. And unfortunately, I don’t foresee fires getting more predictable.”

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Angela Ufheil
Angela Ufheil
Angela Ufheil is a Denver-based journalist and 5280's former digital senior associate editor.