USA – The immense size and intensity of wildfires can level entire communities and consume hundreds of square miles of land. Wildfires can grow so large that they actually alter the atmosphere around them. We’ve seen several recent examples of devastating wildfires in the western United States leading to interesting weather phenomena.
The most interesting videos you’ll see of a wildfire include a fire whirl, sometimes known as a fire tornado, “firenado,” or fire devil. Most of us have seen dust devils form over open fields or large parking lots on hot afternoons. These small columns of rapidly rotating air look like tornadoes, but while some can grow strong enough to cause damage, they’re usually much weaker than tornadoes and tend form under clear skies.
Fire whirls form through a similar process to dust devils, just on a much hotter and larger scale. The immense amount of heat generated by wildfires causes air at the surface to rise quickly. This rising air can start rotating due to winds rapidly blowing into the fire from the outside. The rotation grows stronger through conservation of angular momentum as the column of rising air stretches out. The end result is a fire whirl that’s full of smoke, dirt, and sometimes even the flames themselves. Not only is a fire whirl terrifying to witness, but they can be stronger than dust devils due to the powerful forces involved in their creation.
We’ve seen several strong fire whirls over the past couple of weeks. An intense fire whirl a few weeks ago in Blythe, California, started out over land but moved over a nearby pond and grew to resemble a waterspout. The most recent noteworthy fire whirl occurred on Thursday near Redding, California. The Carr Fire has killed two people as it spread quickly and burned nearly 50,000 acres of land. The inferno is burning so hot that it’s sent smoke and clouds billowing higher in the atmosphere than the cruising altitude of most commercial jets.
Videos taken of the Carr Fire from nearby showed an enormous column of smoke rapidly rotating above the fire. The whirl is so large that it could easily be mistaken for a tornado without any context. The whirling column of smoke was so thick and tall that the rotation actually showed up on Doppler weather radar:
Caption: An animated radar loop showing smoke and winds over the wildfire near Redding, California, on July 26, 2018NOAA/Gibson Ridge
The velocity animation above shows wind moving away (red colors) and toward (green colors) the radar site at Beale Air Force Base, located to the southeast of the fire. The rotation was strong enough that the NWS office in Sacramento, California, issued a special weather statement advising those nearby that strong winds and fire whirls were possible.
Fire whirls aren’t the only way that fires can influence the weather. It’s common to see cumulus clouds develop above large wildfires as rising heat produces updrafts that shoot high into the atmosphere. On rare occasions, these pyrocumulonimbus clouds can turn into thunderstorms. A wildfire in the Texas Panhandle back in May was strong enough that it broke a capping inversion in the atmosphere, allowing a pyrocumulonimbus cloud to develop into a full-fledged supercell that produced large hail a few dozen miles downwind from the fire.