Firenadoes: The Rare Fire-Weather Interaction That Creates Spinning Flame Columns

A Fire Whirl During the 2018 Carr Fire Reached EF3 Tornado Wind Speeds — Without a Supercell

On July 26, 2018, the Carr Fire near Redding, California produced a fire whirl that the National Weather Service subsequently classified as a "firenado" — the first official use of the term in an NWS report — after post-event damage surveys indicated wind speeds of approximately 230 km/h (143 mph), equivalent to an EF3 tornado. The whirl toppled steel transmission towers, produced flying debris damage, and killed firefighter Jeremy Stoke. Unlike a tornado, it formed not from a supercell thunderstorm but from the fire itself: heat-driven convergence of surface winds, combined with existing atmospheric vorticity, organized into a rotating column of flame approximately 300 meters tall. The event prompted the first formal meteorological investigation of fire whirls as a distinct atmospheric phenomenon warranting tornado-scale hazard warnings.

Fire whirls and the rarer true firenadoes represent extreme fire-atmosphere coupling, where a wildfire's heat output drives atmospheric circulation independent of ambient weather systems.

The Physics of Fire Whirl Formation

Fire whirls require two simultaneous ingredients: a strong convective heat source and pre-existing horizontal vorticity tilted into the vertical by that convection.

• Vertical buoyancy: A large wildfire heats surface air to hundreds of degrees, creating an intense buoyant updraft. Superheated air rises at 10–50 m/s in mature fire columns, creating a low-pressure core at ground level that draws in surrounding cooler air horizontally.
• Ambient vorticity: The atmosphere always contains horizontal vorticity from wind shear — layers of air at different speeds or directions creating horizontal rotation. Terrain near ridges, valleys, and canyons generates additional localized vorticity.
• Vortex tube tilting: The intense fire updraft stretches and tilts horizontal vortex tubes into the vertical. As air parcels accelerate upward, conservation of angular momentum spins them faster — the same mechanism that spins an ice skater faster when arms are pulled inward.
• Ground-level convergence: Inflowing surface winds converging on the fire's low-pressure core intensify any net rotational component through angular momentum conservation, organizing the whirl.

Fire Whirl vs. Firenado: Key Distinctions

Historical Firenadoes

The 1923 Great Kantō Earthquake (Mw 7.9) struck at lunchtime when cooking fires were lit across Tokyo and Yokohama. Post-earthquake fires merged and generated a fire whirl over an open area called the Army Clothing Depot in the Honjo district of Tokyo, where approximately 38,000 people had evacuated seeking open space. The fire whirl, estimated by historians to have reached catastrophic wind speeds based on survivor accounts, killed the entire assembly in minutes. It remains the deadliest fire whirl event in recorded history. The 1871 Great Peshtigo Fire in Wisconsin — the deadliest wildfire in US history with approximately 1,500–2,500 deaths — is believed by fire historians to have produced multiple large fire whirls based on damage pattern analysis, though no instrumental records exist.

Pyrocumulonimbus: When Fires Make Their Own Thunderstorms

Large, intense wildfires can generate their own weather systems entirely. Pyrocumulonimbus (pyroCb) clouds form when fire-driven updrafts carry moisture and combustion products high enough into the atmosphere to produce cumulonimbus clouds with lightning, downdrafts, and precipitation — which may evaporate before reaching the surface (virga), creating dry lightning and gusty outflow winds that spread the fire further. The 2003 Canberra bushfires in Australia generated pyroCb clouds reaching the lower stratosphere (16–19 km altitude) that injected aerosols and smoke into the stratosphere, observable by satellite for weeks afterward. Pyrocumulonimbus events have increased substantially as global wildfire intensity increases — NOAA identified pyroCb events in North America at rates 4–5× higher in 2017–2021 compared to 2000–2004.

Atmospheric Conditions That Favor Firenadoes

Research groups at UC Berkeley (Prof. Scott Stephens's fire ecology lab) and CSIRO Australia have conducted controlled laboratory fire whirl experiments using rotating chambers to quantify the relationship between heat release rate and resulting vortex wind speeds. Field instruments deployed during prescribed burns have captured fire whirl vorticity data previously unobtainable, enabling physical parameterization of fire-atmosphere coupling in wildfire behavior models such as WRF-Fire and QUIC-Fire — improving prediction of conditions when firefighter safety may be threatened by sudden fire whirl formation.