Bootleg Fire Incident Command via AP
- The Bootleg Fire in southern Oregon is generating fire clouds and pyrocumulonimbus storms.
- Fire clouds can reach up to 6 miles high; people can spot them from more than 100 miles away.
- Pyrocumulonimbus clouds can generate fire tornadoes and lightning that may spark more blazes.
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Rising temperatures and a growing wildfire are creating dangerous fire clouds and firestorms that can generate their own lightning in the skies above southern Oregon.
The Bootleg Fire, the largest blaze currently burning in the US, has torched more than 241,000 acres (377 square-miles) since it started July 6 in Klamath County. It’s only 7% contained as of Friday.
As heat and smoke from large fires rise skyward, they can create storms comprised of what are known as pyrocumulonimbus clouds. These thunderheads produce their own weather, including tornadoes in rare cases, which can then spark new fires. It’s a vicious cycle.
Bootleg Fire Incident Command via AP
The Oregonian blaze is also creating pyrocumulus, or flammagenitus, clouds – the second word is Latin for “created from flame.”
These fire clouds consist of up to 6-mile-high columns of smoke and ash that are visible from more than 100 miles away. The Bootleg Fire has generated multiple pyrocumulus clouds of this size for the last four days in a row, the Associated Press reported Friday.
Authorities said the clouds form between 3 p.m. and 5 p.m. local time everyday, as heat from the baking ground below rises skyward.
‘Fire-breathing dragon of clouds’
“Pyrocumulus clouds above active fires, especially large fires, are relatively common,” Nick Nauslar from the National Interagency Fire Center in Boise, Idaho told the Los Angeles Times.
But if you spot a bank of thicker, taller thunderheads looming over an intense wildfire, those are almost always pyrocumulonimbus clouds, Nauslar said.
NASA describes pyrocumulonimbus storms as the “fire-breathing dragon of clouds.” They can also generate hundreds of lightning strokes, which in turn can spark more blazes.
In general, thunderstorms form when lots of warm, moist air from the ground rise into the sky. As it enters the lowest part of the atmosphere, that air cools, and then sinks closer to Earth – where it warms up again, and subsequently rises. That cycle of rising and falling air is known as convection, and births cumulonimbus, or thunder, clouds.
But when that heat and moisture rise from a smoky wildfire rather than the ground, the convection creates pyrocumulonimbus clouds.
These anvil-shaped clouds can generate rain like other thunderstorms. Often, though, they unleash powerful, blasts of air known as “downbursts,” rather than water droplets. In pushing dry air back down toward the ground, these downbursts can scatter a blaze’s embers and smoke across large distances. That fuels the flames that generated the storm in the first place.
In September 2020, the Creek Fire in California created one of the largest types of these clouds ever seen in the US – It measured 175,893 acres, or 275 square miles, in size (an area more than three times the size of Seattle).
Thalia Dockery
Rising temperatures and drier air are associated with more frequent and more intense wildfires. And as wildfires increase in size and severity, fire-generated storms, too, are becoming more common.
In 2002, Canada, the US, and Mexico saw about 17 such storms in total. About two decades later, the average number of annual pyrocumulonimbus events had jumped to 25 in western North America alone, Yale360 reported.
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