Predictability issues of heavy Alpine south-side precipitation

Rainstorms on the Alpine south-side that occur during the equinoctial seaso ns are usually accompanied by a single elongated, north-south oriented fila ment of intruded stratospheric air - high potential vorticity air. It was s hown that for these events the predicted precipitation pattern can depend o n the filaments' sub-structure. Based on forecasts for five October months, we examine the synoptic situations where the model performed particularly poorly in predicting these precipitation events. Furthermore precursor flow structures are objectively defined via a statistical analysis of the forec asts. It is shown that an accurate prediction of the precipitation on the Alpine south-side can statistically be linked to the southern part of the high pot ential vorticity anomalies that approach the European continent.