What is a true fire tornado and why did the NWS issue a fire tornado alert on August 15 2020?

Often people call a fire whirl a fire tornado or firenado but just as a dust devil is not a tornado, similarly, fire whirls are not true tornadoes.

Fire whirls are whirlwinds caused by a fire and are usually small in size. Though some can be similar to a landspout tornado, a rope like funnel that forms from a thunderstorm that has no rotating updraft. Landspout tornadoes can be dangerous and the damage caused tends to be EF2 or lower on the Enhanced Fujita scale.

A prerequisite to a true fire tornado is a pyrocumulonimbus cloud which is a Cumulonimbus (Cb) cloud that forms above a heat source like a wildfire but could also form above a volcanic eruption. Supercell thunderstorms which sometimes produce tornadoes also have cumulonimbus clouds. A supercell has a mesocyclone, a deep persistent rotating updraft. This rotation is what can sometimes result in a tornado.

This excellent video explains the proof that the Australian researchers had that a true fire tornado was responsible for the catastrophic destruction during the Canberran bushfires in 2003.

This is the first documented true fire tornado.

The Fire tornado video taken by Tom Bates has a time stamped description of the features of the tornado. The estimated wind speeds in excess of 250km/hr resulted in it being classified as an EF3 tornado.

On July 18 2018, a second true fire tornado was documented in Redding, California. The Carr Fire spawned an EF3 fire tornado. This is also the strongest tornado recorded to date in California.

Another possible fire tornado occurred recently (December 30 2019) in Australia and sadly resulted in the death of a volunteer firefighter when his truck was flipped over.

For the first time the National Weather Service issued a tornado warning due to a fire on August 15 2020. The NWS saw rotation on radar associated with the pyrocumulonimbus cloud from the Loyalton Wildfire in Southeastern Lassen County in northern California and they issued this tornado warning:

They also issued the following related tweets:

Any tornado is dangerous just as any wildfire is dangerous but a fire tornado is even more dangerous especially to firefighters battling the fire.

Teresa Kroeker

References and further reading

https://en.wikipedia.org/wiki/Enhanced_Fujita_scale

https://www.nssl.noaa.gov/education/svrwx101/tornadoes/types/

https://esa.act.gov.au/cbr-be-emergency-ready/bushfires/fire-tornado-video

https://www.sciencenewsforstudents.org/article/californias-carr-fire-spawned-true-fire-tornado

https://www.abc.net.au/news/2019-12-31/rfs-volunteer-firefighter-dies-in-truck-rollover/11833634