Origin of the Precursors to both Extra-tropical Cyclogenesis & Orographically-influenced Heavy Precipitation Events

An enduring challenge for sub-synoptic and mesoscale forecasting is to improve the reliability and extend the useful forecast range for the prediction of extreme weather events. In this presentation attention is given to two such phenomena - intense extra-tropical cyclogenesis and incidents of isolated heavy precipitation on the Alpine south-side. It is asserted that both phenomena are often accompanied by certain distinctive flow features that can serve as early precursors of the events, and moreover that both the deterministic forecast lead-time and the credibility of certain members of a forecast ensemble can be enhanced by identifying the origin of the precursor features. The foregoing assertions are given some credence by examination of the origin, structure and dynamics of the precursors. The examination itself is based upon rudimentary theoretical considerations, and climatological and case study analyses.