Months remain until the peak of wildfire season in the western U.S., but hundreds of blazes have already torched more than a million acres, pouring smoke into the sky and offering an ominous warning of what’s ahead in the fall. Bone-dry conditions and anomalously high temperatures are fostering the perfect recipe for extreme wildfire danger, an issue that will only grow as the winds kick up in August and September.

It’s also making for extreme fire behavior, with rapid growth and spread of wildfires, several of which have grown large enough to create their own weather systems.

The season has already featured the development of fire tornadoes, fire-induced thunderstorms and windstorms, and the ignition of new wildfires through barrages of “dry lightning.”

Red flag warnings blanket much of the northwestern Lower 48, stretching from the Badlands in the Dakotas, west through Montana and Idaho, including the Columbia River Basin, and highlighting parts of Oregon and Washington state as well. That’s where the nation’s largest wildfire is burning.

The Bootleg Fire, located in the Klamath and Fremont-Winema National Forests in southeast Oregon, had burned more than 360,000 acres as of Monday evening. At least 2,200 personnel are involved in the firefighting efforts, but it was still only 30% contained. The fire first cropped up July 6.

“[It] will continue to be extremely active with unstable air conditions and extremely dry fuels,” officials warned Tuesday.

Massive plumes of smoke emanating from the blaze were prompting air quality alerts. The National Weather Service in Medford, Ore., warned residents to “stay inside if possible” and “keep all windows and doors closed.”

“Smoke can irritate the eyes, lungs and worsen some medical conditions,” they wrote.

That’s one of many fires burning across the west. The Dixie Fire, located east of Paradise, Calif., a Butte County city which infamously burned in the Camp Fire on Nov. 8, 2018, killing 86 people, stands at roughly 60,000 acres in size. It’s only 15% contained.

“It produced a large smoke column visible on many of the smoke cameras,” said Scott Rowe, lead meteorologist at the National Weather Service in Sacramento. “We have extraordinarily dry fuels. The ERCs, or energy release components, are at or near seasonal records. That all contributes to the growth of these fires. Since we’ve been having kind of an onshore wind from the south-southwest, the fire goes where the wind goes.”

On Monday, “explosive” development of a pyrocumulonimbus cloud, or essentially a thunderstorm-like cloud made of smoke and water condensate, reached more than 40,000 feet in height. Neil Lareau, a fire specialist and professor of atmospheric sciences at the University of Nevada at Reno, tweeted that the outflow, or downward cool-air exhaust, of one collapsing plume may have helped kick up another almost as tall.

In fact, the plume even grew tall enough to produce rainfall, but much of it evaporated before hitting the ground. Relative humidity levels stand below about 40 to 50%.

Numerous lightning strikes emanated from the fire, raising concern that those strikes could ignite new fires.

“A lot [of fires] have been able to pop up with some pyrocumulonimbus,” said Rowe. “It is only July, and we have a lot of fire season left to go.”

Extreme fire behavior isn’t just an indicator of a robust, potent fire – it presents an incredible danger both to fire officials combating the blaze and to civilians trying to evacuate. In the most extreme circumstances, wildfires aren’t subject to the dominant weather features of the environment. They become the dominant weather feature in their environment.

Serious wildfire pyrocumulonimbus events can produce their own wind, occasionally at speeds exceeding 80 mph. The result is often a firestorm. That can help the fire to grow at breakneck pace, or steer it in unexpected directions. That was a factor in several of the deadly 2018 blazes that ravaged California, including the Paradise Fire. A few had plumes to 50,000 feet.

This season has already witnessed the development of numerous such clouds, primarily in Canada. Following a late July heat wave that smashed the Canadian national record three days in a row and brought a high temperature of 121 degrees in Lytton, British Columbia, dozens of extreme fires broke out and brewed fiery severe thunderstorms.

Between June 30 and July 1, nearly three quarters of a million pyrocumulonimbus-sparked lightning strikes rained down on British Columbia.

Fire tornadoes have been the subject of increasing study and media attention since a deadly funnel struck Redding, Calif. in 2018, producing 143 mph winds and damaging high-voltage power lines. Last year, the Loyalton Fire in northern California spurred the National Weather Service in Reno, Nev. to issue the agency’s first fire tornado warning.

Several fire tornadoes have developed this year, too, including from the Tennant Fire on June 29, which continues to burn east of Siskiyou, Calif., east of Interstate 5 and along Highway 97. Doppler radar initially captured tight rotation commensurate with a likely fire tornado. Pulses of rotation lasted for more than an hour.

It’s likely that more extreme fire behavior is in the offing over the next several months. While the environment, characterized by excessive heat and a pronounced lack of humidity, is a tinder box, winds are a major factor in fueling fire expansion. They usually ramp up during the autumn. Offshore wind events are also effective at drying the landscape even more, particularly on the western slope of hillsides and within mountain valleys.

As climate change continues to foster more extreme heat events and a drying of the West, it’s probable that bouts of extreme fire behavior will continue.

— The Washington Post


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