Fire-generated tornadic vortices (FGTVs) were observed at two high intensity fires in New South Wales during the 2019–20 ‘Black Summer’ Australian bushfires. At the Green Valley Fire, a fully laden fire truck was lifted and overturned by a confirmed FGTV, with estimated wind speeds of ~300 km h–1 (Enhanced Fujita, EF, scale rating of 3 to 4). At Wandella, impact to vehicles at the Badja Forest Fire indicates winds may have exceeded 350 km h–1 (EF5 tornado), making it one of the strongest pyrogenic winds documented globally. We use a combination of observations and insights from simulations using the coupled fire–atmosphere model ACCESS-Fire to investigate the FGTV environments. Radar and satellite observations showed both FGTVs occurred coincident with rapid acceleration of the fire’s updraft and rapid growth of pyroconvective clouds; towering pyrocumulus cloud (pyroCu) at the Green Valley FGTV and pyrocumulonimbus cloud (pyroCb) tops higher than 12 km at the Wandella FGTV. Coupled fire–atmosphere simulations resolved transient, small scale features consistent with observations, including split flow around the fire, reverse lee side inflow, fire updrafts extending to the mid-troposphere, and split fire fronts with convective towers at the head of the flanks. A likely source of vorticity for each was a zone of near ground vertical wind shear between the fire’s reverse inflow in a valley, and north-westerly winds above. The case studies contribute to growing knowledge of these destructive FGTVs, highlight the benefits of fire–atmosphere modelling, and demonstrate the operational utility of radar and satellite observations to inform warnings to communities and fire-fighting operations.
Hanstrum et al. (Wed,) studied this question.