Giant “fire clouds” — 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 — are the latest frightening feature of the wildfires scorching millions of acres in Western states.
On Thursday and Friday, crews fighting the Bootleg fire in Oregon, the largest wildfire burning in the US, had to flee the lines as fire clouds started to collapse, sending strong downdrafts and flying embers to the ground.
These clouds are part of the “extreme fire behavior,” that forecasters say is becoming more common this fire season. There are 70 major fires burning across 12 states right now amid an historic drought.
Fire clouds, or “pyrocumulus clouds” in Latin, look like giant, gray thunderclouds hovering on top of smoke columns. Often, the top of the smoke column flattens out to take the shape of an anvil, The Associated Press reported. But unlike regular clouds, they hold ash and particles from the fire, not just water.
In Oregon, fire clouds have formed each afternoon for the last four days, as the sun penetrated the smoke layer and heated the ground below, which created an updraft of hot air. Crews are seeing the biggest and most dangerous clouds over a section of wilderness that’s made up mostly of dead trees, which burn instantly and with a lot of heat.
Should pyrocumulus cloud grow, it becomes a pyrocumulonimbus, which NASA has called the “fire-breathing dragon of clouds” because they are so hot and big that they create their own weather.
The National Weather Service office in Medford, Ore., tweeted that pyrocumulonimbus clouds formed over the Bootleg fire Wednesday, Thursday and Friday. They were “able to generate in-cloud and cloud-to-ground lightning and strong wind gusts.”
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.
Firefighters working at California blaze last month filmed a firenado that was big enough to get caught on radar.