The National Center for Atmospheric Research (NCAR)/United States National Centers for Environmental Prediction (NCEP) reanalysis data set was used to create proximity soundings in an effort to discriminate between environmental conditions associated with small and large hail events (large hail ≥ 5cm). The proximity sounding approach is restricted by the spatial and temporal distribution of soundings, and additionally, by the quality of severe weather reports. For the Australian region, coastal metropolitan areas account for the majority of the country′s severe weather reports while there is general under-reporting elsewhere. Furthermore, the frequency of documented storm reports has a pronounced spike beginning in 1990, suggesting that prior to 1990, reporting practices were at best inadequate. From 1970 to 1989, there was an average of 15 hail reports per year. Following 1990, the average annual number of reports increased to 77 (1990-1997). On account of the distribution of the population and the severe weather reports, we used several covariates derived from the NCEP reanalysis proximity sounding data to describe the storm environments.

Using this method allowed for a historical look at events where high density, high-resolution data was previously not available. Meteorological variables such as CAPE, 0-1 km wind difference (low-level shear), 0-6 km wind difference (deep shear), mixing ratio, lifted condensation level height, 2-4 km lapse rate, and 700-500 hPa lapse rate were examined for the Australian region from 1970-1999. It is shown that traditional parameters, such as CAPE and deep shear, do not discriminate well for small versus large hail environments as well as they do for hail versus no hail environments (particularly in the U.S.). In addition, several problems are noted on how the NCEP reanalysis grid system may not be the best method for analyzing severe weather events across Australia.