What is a pyrocumulus? Forest fires form “clouds of fire” which represent a danger below


Smoke and heat from a massive wildfire in southeastern Oregon creates giant “clouds of fire” above the blaze – dangerous columns of smoke and ash that can reach up to 10 km in the sky and are visible from over 100 km.

Authorities have placed these clouds at the top of the list of extreme fire behavior they observe on the Bootleg Fire, the largest wildfire in the United States. is raging in a part of the American West that is experiencing a historic drought.

The blaze was so dangerous Thursday night and Friday that authorities withdrew teams. Meteorologists this week also spotted a larger and more extreme form of fire clouds – those that can create their own weather, including “fire tornadoes.”

The extreme fire behavior, including the formation of more fire clouds, is expected to persist on Friday and worsen through the weekend.

What are “clouds of fire?” “

Pyrocumulus clouds – literally translated as “clouds of fire” – look like giant, dirty-colored thunder heads that sit atop a huge column of smoke from a forest fire . Often the top of the smoke column flattens out into the shape of an anvil.

In Oregon, fire departments say clouds form 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 air. hot. On this fire, the crews see the biggest and most dangerous clouds over a part of the wilderness made up mostly of dead trees, which burn instantly and with great heat.

Flames and smoke rise from the Bootleg Fire in southern Oregon on Wednesday, July 14, 2021.

For four consecutive days, the Bootleg Fire generated multiple clouds of fire that rise nearly 6 miles into the atmosphere and are “easily visible from 100 to 120 air miles,” authorities said on Friday.

The conditions creating the clouds are expected to worsen over the weekend.

What is the science behind these clouds?

When the air above the fire becomes superheated, it rises in a large column. As the air with more humidity rises, it rushes up the column of smoke into the atmosphere, and the moisture condenses into droplets. This is what creates the “clouds of fire” which closely resemble thunderstorms seen before a large thunderstorm.

A cloud over the Bootleg Fire, seen here from the Washington Air National Guard, became one of the largest wildfires in Oregon history.

These clouds, however, contain more than water. Ash and fire particles are also swept away there, giving them a dark gray and ominous appearance.

Is there anything more dangerous than a “cloud of fire”?

Yes. When a pyrocumulus cloud forms over a fire, meteorologists begin to watch closely its big brother, the pyrocumulonimbus cloud.

NASA has called the latter the “fire-breathing cloud dragon” because they are so hot and large that they create their own climate.

In a worst-case scenario, fire crews on the ground could see one of the monster clouds spawn a “tornado of fire”, generate its own dry lightning, and create dangerous hot winds below. They can also send column particles of smoke up to 10 miles above the Earth’s surface.

So far, most clouds on the Bootleg Fire have been less intense fire clouds, but the National Weather Service spotted a pyrocumulonimbus cloud forming on what it called images on Wednesday. “terrifying” satellites.

“Please send positive thoughts and best wishes to the firefighters. … It’s a tough time for them right now, ”the weather service said in a tweet.

How dangerous are these clouds?

Both types of fire clouds pose serious hazards to firefighters.

Several pyrocumulus clouds were spotted for four consecutive days, and one on the southern flank of the blaze partially collapsed on Thursday, causing dangerous winds and embers to fall on the crews .

This resulted in the emergency evacuation of all firefighters and earth removal equipment from that part of the fire line. Authorities say no injuries have been reported.

“We expect these same conditions to develop today and worsen even until the weekend,” firefighter spokeswoman Holly Krake said on Friday.

Where else did these clouds form?

These types of fire-induced clouds are becoming more common as climate change lengthens and intensifies the wildfire season in the western United States and other places, including the United States. Australia.

A wildfire in British Columbia last month that wiped out an entire city also generated a cloud of pyrocumulonimbus.

The fires in California in 2020 and in previous years created several pyrocumulus clouds, with the Creek Fire in the Fresno area generating a powerful pyrocumulonimbus cloud last fall.

The siege of the bushfires in Australia in January 2020 also produced pyrocumulonimbus clouds that threatened to produce a tornado of fire.

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