The phenomenon often called a “fire tornado” is scientifically known as a “fire whirl.” These intense, rotating columns of air and flame are a documented hazard during wildfires and other large conflagrations, creating a spectacle that is visually impressive and highly destructive. While these spinning columns share a visual resemblance with true meteorological tornadoes, their underlying physical mechanisms and origin are distinct. The science behind how the intense heat of a fire can generate its own swirling vortex provides a unique look into extreme atmospheric dynamics.
Defining Fire Whirls
The most accurate and widely accepted term for this event is the “fire whirl,” which describes a spinning vortex of air induced by the heat of a fire. These whirls are composed of hot gases, smoke, ash, and often flames, resembling a small tornado. Fire whirls differ fundamentally from true meteorological tornadoes, which descend from a cloud base and are associated with large-scale atmospheric storm systems. A fire whirl, by contrast, is a localized phenomenon generated from the ground up by the fire itself. The vorticity, or spin, in a fire whirl is derived from the intense surface heating and localized wind dynamics near the blaze.
The largest and most destructive fire whirls are sometimes called “fire tornadoes” or “pyrogenetic tornadoes” by atmospheric scientists to denote their extreme intensity. These rare, powerful vortices can reach wind speeds comparable to an actual tornado and may even be associated with the formation of a pyrocumulonimbus cloud, which is a thunderstorm-like cloud created by the fire’s heat and smoke. However, the vast majority of observed events are classified as fire whirls, which remain rooted in the localized heat source.
How They Form
The physical process that creates a fire whirl requires three main ingredients: a source of intense heat, atmospheric instability, and a mechanism for rotation. An intense fire rapidly heats the air directly above it. This superheated air is significantly less dense than the surrounding cooler air, causing it to shoot upward in a powerful buoyant column known as a convection column.
This strong, rising air current acts like a chimney, drawing in cooler air from the fire’s perimeter. If this inflowing air encounters turbulent wind conditions, topographical features, or wind shear, it can begin to rotate. Wind shear—a difference in wind speed or direction over a short distance—is particularly effective at creating the horizontal rolling motion necessary to start the spin.
As the rising convection column stretches this horizontal rotation vertically, the conservation of angular momentum causes the air to spin faster, concentrating the vortex. The resulting fire whirl is a stable, rotating column that sucks in flames, hot gases, and debris, intensifying the combustion and the vortex itself. The continuous supply of heat from the fire sustains the spin, allowing the whirl to persist.
Scale and Danger
Fire whirls vary enormously in size, ranging from small vortices only a few feet high to colossal structures that pose extreme danger. The smaller, more common whirls often last only a few minutes, measuring around 30 to 160 feet in height. These short-lived vortices can still spread embers and accelerate the local burn rate.
The most powerful fire whirls, like the one documented during the 2018 Carr Fire, can grow to over a kilometer (0.6 miles) tall and hundreds of feet wide. Wind speeds within these large fire whirls can exceed 120 miles per hour, which is strong enough to uproot large trees and cause structural damage comparable to an EF-2 or EF-3 tornado. Temperatures inside the core of a fire whirl can reach an estimated 2,000 degrees Fahrenheit, incinerating everything in its path.
These large vortices create a significant hazard by lifting burning materials and embers high into the atmosphere, causing spot fires far ahead of the main fire line. The erratic movement and rapid intensity of fire whirls make them especially dangerous for firefighters, as their formation is often unpredictable and can lead to rapid fire spread.