From a Pyrocumulus to a Severe Thunderstorm: An Environmental Analysis of an Anomalous Southern Plains Wildfire

A rare pyrocumulonimbus (pyroCb) formed over the 30,566 ha Mallard Fire in the Texas Panhandle on 11 May 2018, later becoming a severe thunderstorm that produced 2.5 cm hail 155 km east of Amarillo, TX. This is the second documented instance of a pyroCb-severe thunderstorm evolution on the Great Plains (Jasper Fire in South Dakota, 27 August 2000). Recent improvements in remote sensing, such as GOES-16, allowed unprecedented observation of this highly anomalous transition. A pyroCb typically forms over a wildland fire in an unstable environment with a relatively deep and dry boundary layer characterized by dry-adiabatic lapse rates of temperature and constant mixing ratio. Extreme fire conditions combined with the local terrain and an unstable environment supported pyrocumulus (pyroCu) along the dryline. By the afternoon, the pyroCu matured into a pyroCb just east of the dryline in the eastern Texas Panhandle. Mixed layer convective available potential energy (MLCAPE) values of 2000-2500 J kg-1 and effective bulk wind shear of 15-20 m s-1 supported an environment conducive for sustained convection and potential severe storm development. Given the complex, non-linear wildfire-atmosphere interactions, it is difficult to predict pyroCb development. This study will utilize GOES-16 satellite imagery and WSR-88D observations to examine the transition from pyroCu to a severe thunderstorm. The main objective is to discuss the atmospheric, fuel, and terrain considerations associated with the Mallard Fire severe pyroCb with the goal of improving pyroCb prediction.