A multiscale analysis of the Dolores, Uruguay, tornadoes of 6 December 2012 and 15 April 2016

Abstract

On 15 April 2016, a destructive tornado impacted the town of Dolores, in the Department of Soriano, southwestern Uruguay (SWUY), resulting in one of the most damaging, single-event weather disasters in Uruguay's history. Remarkably, another strong tornado hit Dolores less than four years earlier on 6 December 2012, causing damage in the south portion of the town. This study investigates the Dolores tornado cases in order to document and compare them, with emphasis on the synoptic- and mesoscale environments that led to the two events. It is shown that both tornadoes occurred far downstream of upper-level troughs, under strong mid- and high-level northwesterly winds, and in warm sectors north of warm fronts in southern Uruguay. Key to the development of the tornadic storms was the presence of northwesterly low-level jets that were instrumental in building up conditional instability and low-level shear for tornadic supercells. Based on the the presence of enhanced lines of cumulus clouds noted on visible satellite imagery, it is speculated that local breeze circulations at the northern edge of the Parana river delta or outflow boundaries may have played a role in fostering storm initiation near the Argentina-Uruguay border, although the available data is insufficient to allow for in-depth analyses of these features. Reanalysis-derived soundings reveal that, upon formation, the storms developed in environments characterized by robust conditional instability, deep-layer shear, low-level helicity, low lifting condensation levels, and weak-to-modest convective inhibition, all ingredients favorable for supercell tornado development. This study stresses the need for more research addressing tornadoes in Uruguay and proposes some avenues for future research.