FIRENADOES AND FIRE WHIRLS, ARE SURPRISINGLY FREQUENT OCCURENCES
On March 14, 2014, Participating agencies of the USFWS, USFS, South Metro Fire, West Metro Fire, Denver Fire, and Fairmount Fire districts, engaged in a small localized prescribed burn at the Rocky Mountain Arsenal open space area. During that time, EMT and fire team member, Thomas Rogers, video taped an extraordinary event that turned into a remarkable but short viral documentary of a localized firenado vortex.
From a scientific perspective, this RX firenado was a good visual example of smoke channeled surface wind inflow bands, and a broader but visibly lofted debris field (composed of hundreds of tumble weeds), an interior oscillating fire vortex was fed by 'oxygen enriched' inflow drawn into a rising thermal parcel of significant bouyancy compared with a relatively cooler stable or somewhat descending surrounding air mass, and with a hot flow thermal flux within the vortex core. This relatively small but visible firenado moved approximately one and a half acres.
The slideshow includes March 14th surface METARs and frontal data indicating 63f degree temperatures and 29 dew points, and a boundary layer that indicated a change in surface winds.
The following link is to a Youtube video of the "RX Burn at Rocky Mountain Arsenal on 3/14/2014," and presents a video by South Metro Fire District, EMT member Thomas Rogers, during the prescribed burn of 150 acres at the Rocky Mountain Arsenal in Denver, CO.
FAR FROM BEING UNCOMMON, FIRE TORNADOES CAN OCCUR WITH ALARMING FREQUENCY.
Many other cases of firenadoes have been documented in this decade, including a large one in Australia that had such powerfully rotating winds it split trees, downed forests, demolished homes and flipped cars. According to the UK Register in an article written by Simon Sharwood November 21, 2012, "A fire in Australia grew so powerful that it spawned a tornado nearly 500 metres wide, contributing to the destruction of more than 500 homes. The fire in question hit Australia’s capital city, Canberra, on January 18th, 2003, when eyewitnesses reported seeing a tornado." Australian scientific researchers were able to ascertain that this fire tornado was in fact not just a 'fire whirl' but was actually an EF2 tornado resulting from pyro-cumulus clouds forming an alto cumulus deck that spawned a 'pyro convective' mesocyclone structure, and resulted in a large tornado within the firestorm complex.1-2
"Fire Tornado in Australia, Wildfire Today"1 (November 2012) - http://wildfiretoday.com/tag/fire-tornado/
"An Australian pyro-tornadogenesis event," Richard H. D. McRae, Jason J. Sharples, Stephen R. Wilkes, Alan Walker, (February 2013)2
A significant firenado firestorm in Alaska occurred on August 16, 2013, and managed to gain full wedge-like tornado status, as the main fire tornado mesovortex consumed miles of forest in seconds, with high velocity tornado strength vortex core flow winds were fed by a half mile long surface based flame-fed inflow path (See slideshow).
"Large Alaska Firenado," (August 2013) - Footage taken by Tim Whitesell, Air Tactical Supervisor, and compiled by pilot Doug Burts, Alaska Division of Forestry - http://www.youtube.com/watch?v=lh67J4TNPKE
One recent fire tornado complex in Arizona, also in 2013, resulted in significant casualties, as 19 fire fighters were caught with no escape from the Yarnell, Arizona, fire tornado, as inflow winds seemingly changed direction and the normal path of the progressing fire shifted, while the fire vortex jets then back flowed over their previously safe location, with little or no time for the fire fighters to react.
"Yarnell Hills fire, Arizona," (June 2013) "The smoke had turned and was blowing back on us," Andersen said. "It looked almost like a smoke tornado." - Chicago Tribune
The deadly Waldo Canyon, Colorado Springs forest fire, also developed a large violent firenado complex with such high temperatures within the vortex and canyon walls that temperatures burned in excess of 1,000 degrees turning surface soils into hydrophobic fused sands.
" 'Tornado' of fire had Colorado firefighters fleeing Waldo Canyon" (June 2012) - The Denver Post http://www.denverpost.com/ci_21077853/timeline-waldo-canyon-fire-june-26...
The following link is to an atmospheric science paper discussing fire whirl simulation dynamics and computer modeling.
SIMULATION OF VORTICITY-BUOYANCY INTERACTIONS IN FIRE-WHIRL-LIKE PHENOMENA
NEW VORTEX FIRE SCIENCE IS EVOLVING
Forest fires can, under certain circumstances, develop into powerfully tornadic surface winds with vortices that can produce immediately intensifying and changing fire conditions, and can pose very high threats to life and property.
Additionally, like the large Alaska forest fire in 2013, rapidly rising thermal parcels can develop into cumulus cloud decks (pyro-cumulus clouds), and result in an independent fire-generated weather system. Such pyro-cumulus clouds can either act to enhance the fire dynamic through strong winds, and by randomly discharging lightning bolts into a dry forest environments, or can inhibit forest fires, by depositing rain cooled air and even hail down over the fire that initiated the pyro-cumulus cloud complex in the first place.
More scientific study of pyro-cumulus storms and fire tornadoes is needed, to further Firewise safe practices, and to advance fire fighting science.