In the early evening hours of July 26, a giant fire whirl in Shasta County, California, uprooted trees, overturned vehicles, and downed a transmission tower. The fire whirl persisted for 90 minutes, with maximum wind speeds over 143 miles per hour, which, according to the Enhanced Fujita Scale (used for measuring tornadoes) would rate an EF-3 if it were a tornado (the most severe rating is EF-5).
Its width is estimated to have been about 500 yards, or 87 yards shy of a third of a mile. Eyewitness accounts indicate that it “jumped” over the Sacramento River. It was the sixth most destructive wildfire to strike the Golden State. It resulted in six casualties.
Names attributed to this phenomenon range from fire whirl to fire tornado to fire devil, and firenado. They are spinning columns of air induced by fire, often wreathed in flames or ash and smoke. Intensely rising heat and unstable air patterns signal the beginning of fire whirls.
But these are not tornados. A tornado is a spinning column of air touching both the clouds and the earth. A waterspout, for example, is a type of true tornado, whereas a dust devil or fire whirl, being in contact with the earth but not the clouds, is not.
Fire whirls are driven by surface winds, not an overhead mesocyclone. To date, there has only ever been one confirmed case of a true “fire tornado,” when a fire whirl in the 2003 wildfires in Canberra, Australia, lifted up from the ground, picking up a police car and a fire truck, and dropping them into a storm water drain.
The interior of a fire whirl can reach up to 2,000 degrees and more than 100 feet high, making them extremely dangerous. Wildfires are most likely to produce fire whirls. The most intense include 100 mile per hour winds. While few tornadoes can persist for an hour or more, fire whirls seldom last for more than 20 minutes.
Another danger of the fire whirl is its ability to spew burning debris, which can start new fires. A 1923 earthquake in Japan resulted in mass casualties in Tokyo, much of which were attributed to a giant fire whirl.
Another similarity between fire whirls and actual tornadoes is that the vast majority of each are relatively small and weak, and only a very few exhibit intense severity. As evidenced in California, wildfires can cross rivers and continue moving.
A 2012 study by the U.S. Forest Service has shed some additional light on these flaming vortices. Combusting gasses rising within the core of the vortex result in the lowest regions taking on an orange glow. The diameter can range from four feet (or less) to nearly two miles (six times the width of the California fire whirl).
They can also influence both the speed and direction of the wildfire that spawns them, adding a dangerous unpredictability. A fire whirl in the Indians Fire of 2008, in the Los Padres National Forest, caught firefighters by surprise, seriously injuring some of them.
Autumn is upon us, and it doesn’t look like wildfires or fire whirls are going to be any concern for us. It’s been a wet summer, and that looks to continue, with a sunny mid-October giving way to snow by Halloween.