Meteorological environment of a tornado outbreak in Southern Romania

摘要

On 7 May 2005, a squall line with an embedded bow echo formed over Southern Romania causing severe wind damage. The length of the wind damage was around 150 km. Three tornadoes have been reported, two of them being recorded by video camera. One of the tornadoes occurred in Buftea (near Bucharest), the second in Ciobanu village (near Medgidia radar site) and the third in Movilita village, 40 km to the northeast of Bucharest. The site surveys confirmed wind damage associated with these tornadoes. Based on damage, the Movilita village tornado was classified as an F1 type on the Fujita scale, and the Buftea and Ciobanu village tornadoes were classified as F0. Large scale forcing was provided by a vigorous upper level trough. The squall line developed in the warm sector of a low, ahead of the cold front. The Bucharest EEC-DWSR-2500C Doppler velocity depicted cyclonically rotational structures associated with the left end of the bow echo. In two hours this squall line traversed the southern part of the country. The northern end of the line preserved the bowed structures and high reflectivity gradient in front of them. The dry air associated with the descending rear inflow jet was evident as rear inflow notches in the reflectivity field of the Bucharest C-band radar and the Medgidia S-band WSR-98 D radar. The synoptic and mesoscale environment associated with 7 May 2005 bow echo had many similarities to the "dynamic" pattern described by John and Hirt (1987). Herein are analyzed the combined effects of synoptic and mesoscale circulations, together with the data provided by C-band EEC-DWSR-2500C and S-band WSR-98D radars, and the ECMWF and ALADIN model output data. Some operational aspects of the warning process are also discussed.