Environments associated with hail and convectively generated damaging wind gusts in South America

Abstract

The environmental conditions associated with reports of hail and convectively generated damaging wind gusts in South America are analyzed using the South American Meteorological Hazards and Their Impacts Database (SAMHI) dataset and European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis Version 5 (ERA5) data. The large amount of data in the SAMHI database has made it possible, for the first time, to conduct a study of this kind covering a significant portion of South America. The distributions of several convective parameters for these two hazards, across different severity thresholds, are analyzed. Large hail is favored by moderate instability (often elevated) and high deep-layer vertical wind shear, with effective shear being the parameter that discriminates best between the severity categories. Damaging wind gusts, on the other hand, commonly occur in environments characterized by large surface-based instability, strong vertical wind shear, and strong ground-relative winds within the first kilometer above the ground. An examination of composite parameters developed for other regions suggests that commonly used thresholds for severity potential need to be revised for this region and that a thorough investigation of the specific meteorological regimes in which they are useful is required. By performing clustering analysis on the environments associated with hail events, five different types of environments associated with severe and significantly severe hail were found. This diversity includes cases with moderate surface-based instability with deep-layer unidirectional shear or weak deep-layer shear and high instability. Other cases are often associated with elevated convection, where instability ranges from low to moderate and is concentrated mostly in the hail growth zone. While deep-layer shear is strong in the cases with elevated instability, there is high diversity in hodograph shapes, which can exhibit either mostly straight profiles or large curvature at low levels, indicative of the presence of a low-level jet.