Some of the scarier images coming out of the abundant wildfires this year are fire whirls, or "firenadoes." They are tornado-like swirls of smoke and fire that form in intense wildfires. Despite their popular name, firenadoes more similar to dust devils than they are to tornadoes. How do they form?
Most people are familiar with (or have even seen) a dust devil before. Dust devils are rapidly rotating columns of air that form over large, flat patches of land on days with hot temperatures and light winds. Under the right conditions, the land may be able to heat up enough to cause the air immediately above the surface to quickly start to rise.
When the winds are just right, it may cause the rising column of air to begin to rotate much in the same way that a tornado does. As the column of air continues to rise, it stretches out, causing the column of air to spin more quickly, which kicks up dust and dirt and creates a dust devil.
Some dust devils can reach the intensity of an EF-0 tornado, blowing around light objects and doing damage to poorly constructed buildings. Several people are known to have died from flying debris caused by dust devils.
The same general principle extends to firenadoes. When the right conditions are present, the incredibly intense heat caused by the wildfire allows the air to quickly rise, stretch out, and rotate, creating the "tornado" of fire and smoke.
Regarding the question of whether or not they're dangerous...it's a spinning column of fire reaching a hundred feet into the sky. Of course it's dangerous. The whirl wouldn't be able to survive outside of the wildfire itself, so it wouldn't spread beyond the fire to terrorize a town, but the intense winds are enough to help spread the fire and send it further out of control.
Firenadoes have made the news several times in the last few weeks, including the one spotted in California yesterday (pictured at the top of this post), and an incredible shot of one in Missouri last week.
— Shawn Reynolds (@WCL_Shawn) May 6, 2014
This is not a new phenomenon. The odds of people spotting firenadoes increases with the frequency of wildfires. Not only do more fires provide more chances for these whirls to form, but the fact that almost everyone has a smartphone these days allows people to take a picture and share it with the world the moment they spot one.