Fire Clouds Pose Increased Threat in Southeastern Oregon

The Bootleg Fire, the largest wildfire currently burning in the U.S., has begun to cause the formation of “fire clouds” ⁠— hot, dark clouds which contain both water and ash — over southeastern Oregon.  

There are two types of fire clouds — smaller, more common pyrocumulus clouds and the larger, more dangerous pyrocumulonimbus. Thankfully, many of the Bootleg Fire’s fire clouds are pyrocumulus, but the National Weather Service said on Wednesday, July 14, that they saw some evidence of a pyrocumulonimbus forming over the blaze.  

Although pyrocumulus clouds are less dangerous than pyrocumulonimbus, both types of fire cloud can cause serious danger for people close to a fire — especially firefighters. One pyrocumulous cloud on the southern flank of the Bootleg fire collapsed partially on Thursday, which caused dangerous hot winds as well as ash and some burning embers to fall beneath it. Firefighting crews were forced to evacuate the area as a result, though thankfully no injuries have been reported. 

The dangers of pyrocumulus clouds primarily consist of their tendency to cause weather patterns which blow around smoke, fire and embers. Pyrocumulonimbus clouds, however, can pose more potential dangers. At their worst, these clouds can cause fire-filled tornados and dry lightning, in addition to scattering embers, ash and particulates.  

Fire authorities say the pyrocumulus clouds over the Bootleg fire are most numerous between the hours of 3:00 and 5:00 p.m. when the sun heats up the air under the smoke and causes the clouds to rise and form.   

By Ardea C. Eichner