How Wildfires Make Their Own Clouds

It's been a record year for wildfires in North America, and if current trends hold, it won't just be bad for our forests. The unique and devastating thunderclouds that form above forest fires could also become more commonplace—bringing with them, fire, smoke and pollution that can in some cases spread far beyond wildfire sites.

A typical thundercloud is known as a cumulonimbus cloud. These clouds form when heat rises from a sun-warmed ground and the air has abundant moisture. They look like giant, sprawling anvils that stretch to the top of the sky. A pyrocumulonimbus cloud, on the other hand, is formed when heat rises from an intense fire (this can include volcanic activity, too). These look pretty much as terrifying.

Last year was a banner year for wildfires, leaving "the northern half of the US a hazy, smoky mess," according to a physicist who spoke with Motherboard. This year has been no different—already, Alaska is experiencing its worst wildfire season on record—and it's brought pyrocumulonimbus clouds with it, too.

The first verified pyrocumulonimbus of the 2015 wildfire season was reported to have formed in early May, and scientists believed that high intensity fires later in the month "led to as many as five pyrocumulonimbus events" according to a NASA Earth Observatory post.

There are a few things that make these clouds so much more dangerous than your typical cumulonimbus cloud.

• FIRE. This one is kind of obvious! But hear us out. The intense heat of a forest fire creates what's called an updraft, where air—and sometimes, more fire!—is sucked up into the sky. In some cases, wind can actually carry fiery material (firebrand) to locations nearby, setting even more things ablaze in the process. According to a research paper published by the Australian Bureau of Meteorology and the Bushfire and Natural Hazards Cooperative Research Center, the development of pyrocumulonimbus clouds "can potentially increase firebrand lofting heights by three to five times, which greatly increases the potential firebrand transport distances."

• LIGHTNING. According to the same Australian report, dry environments where there is also the presence of smoke are even more likely than typical thunderclouds to exhibit positively charged cloud-to-ground lightning—"the most dangerous as they contain long periods of continuous current, […] exhibit the greatest peak current, and carry the largest charge transfer to the ground," the report reads. Needless to say, this isn't exactly a good thing, as this type of positively charged lightning can wreak yet more havoc upon objects on the ground that haven't already been set aflame.

• POLLUTION. According to NASA, "Scientists monitor pyrocumulonimbus clouds closely because they can inject smoke and pollutants high into the atmosphere. As pollutants are dispersed by wind, they can affect air quality over a broad area affecting areas far from the fire site." This is also not a good thing.

So, yeah, pyrocumulonimbus clouds are serious business and should be rightly feared—and we might just have to get used to them, because it doesn't look these fires are going to stop anytime soon.