engleski

Flash-flood in Pula, in the North Adriatic in the night of 24 to 25 September 2010

A case with the extreme precipitation is analysed by means of measurements and NWP model data. The satellite, radar, lightning and rain-gauge data were included, whereas for the forecast part ECMWF and ALADIN models were used. Synoptic analysis showed a deep upper-level trough stretching from western Scandinavia to the Gulf of Genoa with the secondary trough located over Sicily. The low- level situation was characterized by the south- easterly flow at the front side of a cyclone moving eastwards through the Tyrrhenian Sea. In the afternoon of the 24th scattered showers in the area started, intensified and spread to the whole North Adriatic basin. According to the radar data the hourly precipitation amounts exceeded 50 millimeters. Around midnight second cyclone in the Gulf of Genoa caused the strong convergence along the west coast of Istrian Peninsula. Pronounced vertical wind-sheer induced severe convective development in the vicinity of the horn of Istria moving over the land and producing almost 200 mm of rain in less than 6 hours. In south-western Istria roads and settlements were flooded. The rain-gauge amount of 176 mm is the highest daily value ever measured in city of Pula. Operational 8km resolution hydrostatic ALADIN model forecast the existence of twin cyclones quite satisfyingly giving the correct precipitation maximum over the sea. Nevertheless, there was no indication for the secondary maximum over the Istrian land. The processes that lead to the development of the secondary maximum were further explored using the 2km resolution non-hydrostatic ALADIN model.

severe rain; flash flood; convection

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