Predictability Issues of Heavy Alpine South-Side Precipitation

Summary

 Rainstorms on the Alpine south-side that occur during the equinoctial seasons are usually accompanied by a single elongated, north-south oriented filament of intruded stratospheric air – high potential vorticity air. It was shown that for these events the predicted precipitation pattern can depend on 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 forecasts.

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 potential vorticity anomalies that approach the European continent.