EUMeTrain: Case Study on severe Convection over Central Europe

Convection over Croatia on 22^nd and 23^rd June 2007

Authors

Meteorological and Hydrological Service of Croatia - DHMZ

Dunja Placko-Vrsnak
Natasa Strelec Mahovic
Dunja Mazzocco Drvar

Introduction

In the late evening of the 22nd and during the night of the 23rd of June 2007, the region of the North Adriatic, Lika, north-eastern and eastern part of Croatia were devastated by a severe storm. Hail on the island of Rab (North Adriatic) was the size of an egg or even a peach; at the other parts hail was the size of hazelnuts or walnuts. Serious damages of property (cars, roofs, trees, orchards, crops) were reported.

The whole process of the development and convective events over Croatia and partly over Bosnia and Hercegovina are discussed in detail with help of the radar data as well as the relevant NWP parameters and nowcasting products.

Hail on the ground and grass (5-10 cm) in Slatina, north-east part of Croatia on 23rd June	Hail on the island of Rab (North Adriatic), size of an egg, in the late evening of 22nd June

In the strong SW flow over Croatia the humid and warm air was coming from the West Mediterranean in the front of the cold front. The very hot period, with temperature exceeding 30 °C, was experienced all over the country in previous days. Strong convective activity occurred during the night of the 22nd June in the coastal regions of the North Adriatic and during the early morning of the 23rd in the central and north-east part of Croatia (Podravina and Slavonija), caused by orography and passage of the cold front. A lot of thunderstorms, rain and hail were reported.
Dinaric Alps triggered the convection over the western part of Croatia.

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	Accumulated rainfall (24 hours) during the event was from 0 to 25 mm in the western, central and north-eastern part of Croatia.
Total precipitation during 24 hours from 22nd to 23rd June 06 UTC

Hail occurred in the western, central and north-eastern part of Croatia. Over the continental part of Croatia hail observations and measurements are done during spring and summer months by the observers on the hail stations by the hail-pad network. The region is also covered by 2 radars. Along the Adriatic coast there are unfortunately no radars and no data about hail (duration, size, damage).
The observed average hailstone diameter over the continental part was up to 25 mm with duration of hail from 2 to 10 minutes. According to the hail-pad measurements, given in the images below, the maximum hailstone diameter was 24,9 mm.

Appearance of hail from 2200 to 0430 UTC on 22nd and 23rd June measured by hail-pads Click to enlarge.	Mean diameter of hail measured by hail-pads during 22nd and 23rd June Click to enlarge.