Atmospheric profiles associated with pyrocumulonimbus in southeast Australia

Pyrocumulonimbus (pyroCb) are thunderstorms generated by wildfires. They present significant risks to first responders and civilian populations in southeast Australia and in many regions around the world. PyroCb are increasingly common in southeast Australia, with the majority of recorded events occurring in the last 20 years. We constructed, examined, and statistically compared median atmospheric profiles for pyroCb-producing and large standard (non-pyroCb-producing) wildfires in the southeast Australian mainland over a 30-year time period (1991-2020). We found that pyroCb in southeast Australia frequently develop on days with hot, relatively dry, very unstable, and moderately windy surface and low-level conditions that are favourable for wildfire spread. These conditions often occur in conjunction with steep mid-level lapse rates and significant diurnal mid-level moisture advection, resulting in conditions at least conditionally favourable for high-based thunderstorm development. PyroCb and standard wildfire events have similar wind profiles, particularly in the lower-levels, but pyroCb tend to be associated with lower winds in the mid- and upper-levels of the troposphere. However, variability within the pyroCb-related data suggests that pyroCb in southeast Australia can form in a variety of atmospheric conditions. These results may have important implications for forecasting pyroCb potential.