Smoke and heat from the massive wildfire created "fire clouds" (pyrocumulus clouds) over the Bootleg Fire in southern Oregon - dangerous columns of smoke and ash that can reach up to 30,000 feet and are visible for more than 100 miles away. Authorities put these clouds at the top of the list of the extreme fire behavior they saw on the largest wildfire burning in the U.S. This July 14 photo was taken with a drone provided by the Bootleg Fire Incident Command.
PORTLAND - Smoke and heat from a massive wildfire in southeastern Oregon created giant "fire clouds" over the blaze - dangerous columns of smoke and ash that can reach up to 6 miles in the sky and are visible from more than 100 miles away.
Authorities put these clouds at the top of the list of the extreme fire behavior they saw on the Bootleg Fire, one of the largest wildfires in Oregon's recorded history. The inferno covered nearly 650 square miles - larger than the size of New York City - as it raged through a part of the U.S. West that is enduring a historic drought.
Meteorologists also spotted a bigger, more extreme form of fire clouds - ones that can create their own weather, including "fire tornadoes."
Pyrocumulus clouds - literally translated as "fire clouds" - look like giant, dirty-colored thunderheads that sit atop a massive column of smoke coming up from a wildfire. Often the top of the smoke column flattens out to take the shape of an anvil.
In Oregon, fire authorities said the clouds formed between 3 p.m. and 5 p.m. each day as the sun penetrates the smoke layer and heats the ground below, creating an updraft of hot air. On this fire, crews saw the biggest and most dangerous clouds over a section of wilderness that's comprised mostly of dead trees, which burn instantly and with a lot of heat.
For four days in a row, the Bootleg Fire generated multiple fire clouds, authorities said. The fire was essentially fully contained last week, after burning for a month.
When air over the fire becomes super-heated, it rises in a large column. As the air with more moisture rises, it rushes up the smoke column into the atmosphere, and the moisture condenses into droplets. That's what creates the "fire clouds" that look much like the thunderheads seen before a big thunderstorm.
These clouds, however, hold more than just water. Ash and particles from the fire also get swept into them, giving them a dark gray, ominous look.
And when a pyrocumulus cloud forms over a fire, meteorologists begin to watch carefully for its big brother, the pyrocumulonimbus cloud.
NASA has called the latter the "fire-breathing dragon of clouds" because they are so hot and big that they create their own weather.
In a worst-case scenario, fire crews on the ground could see one of the monster clouds spawn a "fire tornado," generate its own dry lightning and hail - but no rain - and create dangerous hot winds below. They can also send particulate matter from the smoke column up to 10 miles above Earth's surface.
Most of the clouds on the Bootleg Fire were the less-intense fire clouds, but the National Weather Service spotted a pyrocumulonimbus cloud forming on what it called "terrifying" satellite imagery.
"Please send positive thoughts and well wishes to the firefighters. ... It's a tough time for them right now," the weather service said in a tweet.
Both types of fire clouds pose serious risks for firefighters.
Multiple pyrocumulus clouds were spotted for four consecutive days, and one of them on the southern flank of the fire partially collapsed, causing dangerous winds and embers to fall on crews.
That prompted the emergency evacuation of all firefighters and dirt-moving equipment from that part of the fire line. Authorities said there were no reported injuries.
These types of fire-induced clouds are becoming more common as climate change lengthens and intensifies the wildfire season across the U.S. West and in other places, including Australia.
Experts with the U.S. Naval Research Laboratory said in a news release Aug. 6 that they are seeing a "record number" of these fire-induced clouds in North America this summer, including in Oregon, Montana and British Columbia.
For example, a wildfire in British Columbia last month that leveled an entire town also generated a pyrocumulonimbus cloud.
Blazes in California in 2020 and in the years before have created multiple pyrocumulus clouds, with the Creek Fire in the Fresno area generating a mighty pyrocumulonimbus cloud last fall.
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