Abstract
Abstract. 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.
Highlights
Bow echoes are a unique form of convective organization that often produces severe weather, especially damaging straightline winds and tornadoes. Fujita (1978) realized the first well-known conceptual model with his schematic (Fig. 1a) that shows how an initial straight echo transforms into a bow-shaped line of convective cells with the strongest winds occurring at the apex of the bow
On 7 May 2005, a squall line with an embedded bow echo formed over Southern Romania causing severe wind damage
– The squall line with an embedded bow echo formed along a surface thermal and moisture boundary line ahead of the surface cold front associated with a strong low pressure system
Summary
Bow echoes are a unique form of convective organization that often produces severe weather, especially damaging straightline winds and tornadoes. Fujita (1978) realized the first well-known conceptual model with his schematic (Fig. 1a) that shows how an initial straight echo transforms into a bow-shaped line of convective cells with the strongest winds occurring at the apex of the bow. Forecasting and monitoring potentially severe thunderstorms with high intensities for wind speed, high rainfall rate and hail in the context of the variety of Romanian relief constitutes a significant challenge, because in most cases, various kinds of severe weather occur simultaneously This was the situation on 7 May 2005, in Southern Romania, when tornadoes, high winds and hail affected the plain region from the south of the country, and torrential rain in the hilly part that produced, in the interval immediately following, a major flash flood. This case is interesting meteorologically, and because it shows how the simultaneous occurrence of severe whether events can decrease the efficiency of the operational weather short term forecasting system. We will compare synoptic and mesoscale features associated with the formation and evolution of the 7 May 2005 bow echo with conditions that favor bow echo development in USA observed by Johns and Hirt (Johns and Hirt, 1987; Jonhs, 1993)
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