Extreme precipitation events over northern Italy. Part <scp>II</scp> : Dynamical precursors

The connection between weather extremes and Rossby wave packets (RWP) has been increasingly documented in recent years. RWP propagation characteristics can modulate the midlatitude weather, setting scene for temperature precipitation controlling geographical area affected. Several studies on extreme events (EPEs) Alpine reported, as main triggering factor, a meridionally elongated upper-level trough part of an incoming packet. In this work, we investigate wide number EPEs occurring 1979 2015 northern-central Italy. are subdivided into three categories (Cat1, Cat2, Cat3) according to thermodynamic conditions over affected region. It is found that differ not only terms local meteorological conditions, but also evolution properties precursor RWPs. These differences cannot be solely explained by apparent seasonality flow; therefore, relevant physical processes each case further investigated. particular, show RWPs associated with strongest EPEs, namely ones falling undergo substantial amplification western North Atlantic due anomalous ridge-building 2 days before event; arguably diabatic heating sources. This type development induces downstream which highly effective focusing water vapour transport toward orographic barriers Italy favouring occurrence EPEs.