Observed versus forecasted precipitation in the South East Alps

Intense precipitation events are common on the SE slopes of the Alps and the climatological maximum of precipitation is located in the area of the Julian and Carnic Alps. Mesoscale intensification of rainfall in the area is explained. Two cases of intense precipitation were studied with fine mesh mesometeorological modelling using the ALADIN-SI model and verifying its results with all available ground-based raingauge measurements. For the first case of 5-8 November 1997 mesoscale topographically induced direct lifting was the main reason for precipitation intensification in the area. For the second case of 3-5 November 1998 this forcing was further modified by a mesofront moving along the eastern edge of the Alps in the opposite direction to the flow at upper levels. In the predicted precipitation the most noticeable feature was the shift of the forecasted precipitation fields by some 20 km with respect to the measured one leading to overestimation at the SW side, and underestimation at the NE side of the mountain ridge. The role of discrepancy sources of differences between the forecasted and raingauge precipitation are evaluated