engleski

Synoptic and mesoscale environments conductive to heavy precipitation during MAP IOP5

A high resolution climatology of yearly precipitation for Alpine area has been provided by Frei and Schär (1998). Intense precipitation events are common on the SE slopes of the Alps. Two pronounced maxima of accumulated precipitation appear in SE Alps: the Julian Alps in W Slovenia and NE Italy's Friuli-Venezia Giulia region, and in W Croatia in the Dinaric Alpine region. Mesoscale intensification of the MAP SOP heavy precipitation occurred on 4 October 1999 along the border of Slovenia and western part of Croatia is explained. Large amount of rain was caused at the frontal zone modified by the convergence between the southerly winds associated with the Alpine lee cyclogenesis and the northerlies blowing around the eastern flank of the Alps after the process of splitting currents on the north Alpine orographic blocking. This convergence was responsible for the formation of rainband with convectively unstable air advected by the warm and humid current from the Mediterranean. The numerical results of HRID with pseudotemps of ALADIN/LACE mesoscale prognostic model and TEMP messages for 3-hourly time intervals in Zagreb and 6-hourly intervals in Ljubljana and Udine were used for the verification of presented HRID vertical time cross sections. It is shown that the relative forecast error did not exceed 4 percent. Thus, forecast of presented vertical atmospheric structure offers very satisfactory results considering that it was an extraordinary case with a rapid frontal development. It is therefore concluded that the postprocesssing of HRID with ALADIN/LACE forecasting pseudotemps could be successfully used especially in the preparation of nowcasting procedure.

heavy precipitation; lee cyclogenesis; flow splitting; convectively unstable air; ALADIN/LACE; HRID

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