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1 2015

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The forecasting of tornado events: the synoptic background of two different tornado case studies

Wrona B., Avotniece Z.

Meteorology Hydrology and Water Management. Research and Operational Applications

2015

Vol. 3, Iss. 1

51--58

The synoptic analyses of two different tornado cases, observed in Latvia and Poland in the summer of 2012, are examined in this paper. The first of them, the tornado in Latvia seemed to be a “textbook example” of tornado occurrence. Its development took place in the contact zone of the warm, tropical air, characterized by a very high CAPE (Convective Available Potential Energy), with cold and moist polar marine air mass behind the convergence line that determined very good conditions for convective updraft. Additionally, the moderate environmental wind shear favoured the sufficient condition for concentrating the atmosphere’s vorticity into well-organized strong rotating upward motions that produced the supercell structures and tornado. Thus, from the forecaster’s point of view, the occurrence of this severe convective event was not a surprise. This phenomenon was predicted correctly more than a dozen hours before the tornado occurred. The second event occurred in the north of Poland and was associated with a thunderstorm where a supercell was formed in conditions of low CAPE but favourable wind profile, both vertical and horizontal. Helical environments (characterized by large shear vectors that veered with height in the lowest three kilometres, especially the nearest one kilometre) were arguably the most important factor that determined the Polish tornado’s occurrence. In this case the analysis of the synoptic situation was not so clear and the superficial analysis, even post factum, regarding radar, satellite or detection maps might have suggested “quite a normal” summer thunderstorm. However, the detailed examination showed the reasons why tornado genesis took place. The potential conditions for the occurrence of this severe phenomenon were indicated by forecasters, although the forecasts were less exact with regard to the place of occurrence and the heaviness of the strike.