Hybrid probabilistic forecast scheme for postfrontal shower precipitation

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A hybrid forecasting scheme for post-frontal convective shower precipitation is proposed. The deterministic forecast of the post-frontal convective precipitation field is combined with a probabilistic precipitation forecast for the individual rain areas contained therein. The rationale for this approach is the observation that ensembles of convective rain areas (CRAs) are in statistical equilibrium with synoptic scale conditions. Their characteristics follow simple universal laws, remain constant, if properly scaled and follow seif-similar distributions as was shown by THEUSNER AND HAUF (2003). The statistical properties are homogeneously distributed within Germany, except for the Alps and the coastal zone. Furthermore, individual rain areas seem to move more or less in a uniform matter given by the synoptic flow. The hybrid scheme forecasts statistical means of: number of CRAs, total rain area, areal precipitation, maximum local precipitation, rain duration; furthermore the local precipitation likelihood and other statistical quantities. Essential part of the work are (i) the extension of own previous work to include for rainfall rates based an common radar-reflectivity relationships, and (ii) the investigation of synoptic influence an the statistical properties, including the sampling errors. The scheure will be tested and evaluated following the methods proposed by KIRK AND FRAEDRICH (1998).