Analysis of a Case of Supercellular Convection over Bulgaria: Observations and Numerical Simulations

Hristo G Chipilski,Xuguang Wang,Tsvetelina Dimitrova,Lilia Bocheva,Ivan Tsonevsky,Stefan Georgiev

doi:10.3390/atmos10090486

Abstract

A long-lived supercell developed in Northwest Bulgaria on 15 May 2018 and inflicted widespread damage along its track. The first part of this article presents a detailed overview of the observed storm evolution. Doppler radar observations reveal that the storm acquired typical supercellular signatures and maintained reflectivity values in excess of 63 dBZ for more than 4 h. The thunderstorm was also analyzed through lightning observations that highlighted important characteristics of the overall supercell dynamics. In its second part, the study investigates the predictability of the severe weather outbreak. In the medium forecast ranges, the global European Centre for Medium-Range Weather Forecasts (ECMWF) ensemble indicated the presence of favorable conditions for the development of deep moist convection 4 days prior to the event. A set of three convection-allowing ensemble simulations also demonstrated that the practical predictability of the supercell was approximately 12 h, which is considerably higher than some previously reported estimates. Nevertheless, the skill of the convective forecasts appears to be limited by the presence of typical model errors, such as the timing of convection initiation and the development of spurious convective activity. The relevance of these errors to the optimal ensemble size and to the design of future convection-allowing numerical weather prediction (NWP) systems is further discussed.

Highlights

Severe thunderstorms exert significant socio-economic impacts in Europe [1,2,3]
Numerical simulations [8,9,10] have shown that supercell storms can be distinguished from ordinary thunderstorms by specific dynamical processes involved in their development
The cell moved towards the northeast, but its propagation direction gradually attained an easterly component as the storm evolved into a powerful supercell

Summary

Introduction

Better understanding of the processes which lead to severe convective storms, as well as their regional characteristics, is of primary importance. The development of the European Severe Weather Database (ESWD) [4] allowed for important research on the climatology of severe convective storms on a pan-European scale [5] and on the environmental conditions for severe thunderstorms in Europe [6]. The supercell, characterized by the presence of a rotating updraft or mesocyclone [7], is perhaps the best known example of organized convection, and it is often associated with major outbreaks of severe convective weather. Numerical simulations [8,9,10] have shown that supercell storms can be distinguished from ordinary thunderstorms by specific dynamical processes involved in their development. Strong vertical wind shear can lead to the development of nonhydrostatic pressure gradients which contribute to the generation of strong updrafts [8]

Objectives

Results

Conclusion