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Menopausal Mother Nature

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See How the Dixie Fire Created Its Own Weather

Over its lifespan, the Dixie fire generated eight firestorms and displayed other extreme behaviors, including at least one fire whirl, a sort of mini-tornado. David Peterson, a meteorologist who tracks fire-driven thunderstorms at the U.S. Naval Research Laboratory, called Dixie “the most prolific producer of pyroCbs” in the United States this summer.

These storms create “a very dangerous situation for our firefighters on the ground,” said Edwin Zuniga, a public information officer for Cal Fire, California’s firefighting agency.

When wildfires are driven by wind, they usually move in a predictable direction. “If the wind is blowing from the southwest, we know the fire will be travelling to the northeast,” Mr. Zuniga said. But fires that are “plume-dominated” — like those creating and sustaining their own weather systems — are more volatile. They spew their own erratic winds and can throw embers long distances, causing spot fires miles away.

Faced with pyroCb clouds, firefighters are usually forced to pull back from a blaze. “It’s really nearly impossible to contain at that point,” Mr. Zuniga said.



Cal Fire firefighters battling the Dixie Fire near Milford, Calif., this summer.Patrick T. Fallon/Agence France-Presse/Getty Images

Since it began in July, when a small cluster of flames was discovered near downed power lines, the Dixie fire has burned through nearly a million acres across the Sierra Nevada, triggering mass evacuations and destroying thousands of homes, businesses and other structures, including much of the town of Greenville.

Today, the fire is almost fully contained, though pockets still smolder.

Competing forces helped Dixie grow into a monster, said Ryan Bauer, a fire manager at Plumas National Forest. Strong winds often pushed flames across the rugged terrain of the Sierra. But even when the winds were calm, the fire created its own momentum, kicking up powerful plumes and pyro-clouds.

Recent extreme heat and drought had turned California’s overgrown forests into potent fuel for either scenario. “The stage was set for fire to spread no matter what the conditions,” Mr. Bauer said. “It was just a matter of whether it was going to be wind-driven that day or plume-dominated.”






Eagle Lake

Sierra Nevada

CALIFORNIA

Dixie fire

Janesville

Lake Almanor

Honey Lake

Dixie

fire

Greenville

Sierra Nevada

CALIFORNIA

Dixie fire

Janesville

Dixie

fire

Greenville

Sierra Nevada

CALIFORNIA

Dixie fire

Dixie

fire

CALIFORNIA

Dixie

fire

Dixie fire


Note: Graphic reflects the extent of the fire at the end of the day for each date.·Source: CalFIRE

Wildfires on the West Coast have grown larger and more intense in recent years, especially in California. Experts attribute the trend to a combination of factors, including decades of aggressive fire suppression that left forests dangerously overgrown, and climate change, which has parched the landscape, priming it to burn at record scale.

Fire clouds have also become increasingly common on the landscape. In California, where powerful infernos have burned close to population centers, snapshots of the mushroom-like clouds have spread widely on social media.

Dr. Peterson’s team recorded 33 pyroCb clouds in the American West this year, tying a record set in 2013.






Aug. 13, 2021

PyroCb

cloud

Antelope fire

Dixie fire

McFarland fire

CALIFORNIA

Aug. 13, 2021

PyroCb

cloud

Antelope fire

Dixie fire

McFarland fire

CALIFORNIA


Source: National Oceanic and Atmospheric Administration; David Peterson

It’s not yet clear whether there is a sustained long-term trend toward more fire-fueled storms, in part because the record of these events is still relatively short: An effort to consistently track pyroCb formation across the globe, based on satellite observations, dates back about a decade.

What is clear is that the ingredients necessary for firestorm activity — drier landscapes that support larger, more intense fires; more atmospheric instability, which aids the development of thunderstorms; or both — are becoming more common in many parts of the world as human-caused climate change pushes temperatures higher.

Following a historic heat wave early this summer, Western Canada experienced a particularly explosive run of pyroCb activity. On two occasions, the powerful storm clouds grew so tall — the largest reached an altitude of 57,000 feet — that they broke through the lower atmosphere and injected smoke into the stratosphere. The smoke particles can linger in this layer for months and make their way around the globe, which can even lead to some temporary regional cooling.

Firestorm clouds have regularly been documented in Western North America, Southern Australia and across much of Siberia, where wildfires are seasonal events. But extreme fire weather is now occurring in less expected places, too: A pyroCb cloud formed north of Athens this year, part of a disastrous outbreak of summer wildfires.

“We’re creating an environment that favors these positive feedbacks, where the fire makes itself worse,” said Dr. Lareau, an assistant professor at the University of Nevada, Reno. “It tips the balance between what may have been an ordinary fire in decades past and a fire that can grow into a megafire.”

How we built the 3-D model

The Dixie fire’s smoke and clouds were created using reflectivity data from three Next-Generation Radar network stations collected on July 19, 2021, between 11:00 a.m. and 11:00 p.m, Pacific Daylight Time.

The raw data was collected every 10 minutes in radial sweeps around the radar stations, each at a higher altitude. The Times combined and reformatted the data using Py-ART, a collection of algorithms and utilities used regularly in radar analysis. We then filtered it to reduce noise.

We applied color and texture to the 3-D volume to approximate a smoke- and cloud-like look. And we interpolated the sequence in time to create a smoother video animation.

The radar volume rendering was based onprevious work by Dr. Lareau of the University of Nevada, Reno.

The lightning strikes were recorded by the Vaisala Lightning Detection System. We only showed strikes that reached the ground.

The terrain was created using topographic data from the U.S.G.S. 3-D Elevation Program and color imagery from the Copernicus Sentinel-2 satellites, retrieved at a resolution of 10 meters. To eliminate 2-D cloud cover on the landscape, we generated a composite of satellite images from June 1 to June 30, 2021.

The fire footprint was created by combining perimeter data from the California Department of Forestry and Fire Protection along with fire detections data from NASA’s Fire Information for Resource Management System and the U.S. Forest Service Active Fire Mapping Program.

Additional expert sources

•  Michael Fromm, meteorologist at the U.S. Naval Research Laboratory

•  Daniel Swain, climate scientist at the University of California, Los Angeles

•  Rich Thompson, incident meteorologist at the National Weather Service, Los Angeles/Oxnard

Additional credits

Produced by Michael Beswetherick

Photo editing by Matthew McCann

Additional work by Or Fleisher, Sam Manchester and Jeremy White

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