A case study of tornado-producing storm south of Rhodopes mountain in the Eastern Mediterranean

Abstract

A brief overview of tornadic events (wind spouts) over Bulgaria in the period 1904–1989 that have been recorded in the meteorological archive and described in scientific papers is presented. The local tornado (spout) on 15 May 1999 in Zhaltusha village (south of Rhodopes mountain in the most southern part of Bulgaria, close to the Mediterranean coast) is studied in detail. The case is associated with hail (‘egg-shaped’ stones about 5 cm in diameter) and caused damages of property valued above US$250 000. The high-wind-speed vortex blew off house roofs, rooted out trees, and turned over trucks. Using numerical model analysis fields and satellite imagery, evidence is presented, which illustrates the role of synoptic scale mechanisms for the generation of the severe storm. On the large scale, the circulation pattern is associated with a trough disruption process over the area of Western Europe, North Atlantic and Mediterranean. Under the influence of southwestern flow in the lower troposphere, warm and moist Mediterranean air is advected in the region of strong westerlies in the higher levels. Together with the role of low-level warm/moist advection and westerly transport of cold air at the mid-upper levels, diurnal heating, terrain-induced lifting, etc., are also critical for the initiation of deep convection over the region of tornadic event. As a result of these factors, a typical cloud pattern developed that indicates the existence of a local area of negative vertical gradient of the thermal advection in the troposphere, associated with the dramatic destabilisation. Other synoptic- and mesoscale elements may also be revealed or confirmed by satellite and radiosonde data. The nearest Rhodopes radiosounding (at Thessaloniki airport) and surface meteorological data from Kurdjaly station are used for air mass analysis in the vicinity of the storm. The obtained result shows very high values of atmospheric instability indices (the energy E i=3327 J/kg K, TT I=45.6°C, K I=16.5°C). The updraft was up to 20 m/s and the difference of wind velocity at 300- and 700-hPa levels was up to 10 m/s. Cloud water content reached up to 12 g/kg.