An 11‐year climatology of thunderstorm hours and associated environments in Australia

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This study presents an 11‐year climatology of thunderstorm (TS) hours and associated environments in Australia, based on ground‐based lightning observations and a regional reanalysis. Spatial and temporal variations in TS frequency are explored using heat maps and a cluster analysis applied to the average seasonal and diurnal cycles of TS at every grid point. TS environments are characterised using a mixture of standard reanalysis variables and convective parameters derived from the full‐resolution model‐level data. The ability of these diagnostics to discriminate between hours with and without TS is quantified using scores based on the contingency table and visualised using “skill pyramids”, a novel variation on the widely used relative operating characteristic (ROC) diagram. Consistent with previous global and regional climatologies, the highest TS frequencies are found in the tropical north of Australia, with secondary maxima over areas of elevated topography and the Tasman Sea. Large seasonal and diurnal variations are observed over most land areas, with TS frequencies peaking in the afternoon and evening during the warm season. Sea breezes appear to play a dominant role in the development of TS in many coastal regions. In the tropics, a local minimum in TS activity is identified over land during the peak of the monsoon season, while a nocturnal maximum is observed offshore. Environmental analysis suggests that elevated TS are more common at higher latitudes, while the vast majority of tropical TS are surface‐based. In general, measures of instability above the freezing level and mid‐level moisture provide good discrimination of TS hours across Australia, though skill is consistently poorer in the tropics. Surprisingly, traditional stability indices are among the best‐performing TS predictors across all regions. This is hypothesised to reflect their consideration of instability and moisture above the boundary layer, which can modulate the intensity of convective updrafts via entrainment.