Identifying severe thunderstorm environments in southern Brazil: analysis of severe weather parameters

Given that the occurrence of (mid-latitude) severe convective storms in southern Brazil is not as rare as previously thought, there is an increasing need for the assessment of operational strategies aiming at the identification of atmospheric conditions conducive to severe weather in that part of the world, as a support for disaster mitigation.

This article addresses a pre-operational initiative in this context, where severe weather parameters, originally conceived for the mid-latitudes of North America, are evaluated for severe thunderstorm forecasting in southern Brazil. Convective indices analyzed include storm-relative-helicity, bulk Richardson number shear, storm-relative winds at different levels, energy-helicity-index, supercell composite index and normalized CAPE, along with more classic parameters such as surface-based CAPE and the lifted-index. In this study, data from rawinsondes in southern Brazil and from mesoscale model output for that part of the country are used covering the period from years 2003 and 2004. Although preliminary, our results are encouraging given that the severe weather indices did highlight atmospheric conditions associated with the actual occurrence of damage-producing convective storms.