In this paper, the mechanism and model-representation of a late-spring severe blizzard event on eastern Romania are studied. The mechanism relies on the coupled contribution of the tropospheric ageostrophic circulations associated to jet streaks. These circulations: (1) interact under local and regional forcing (sea surface temperature, topography and latent heat) and (2) feedback on enhancing an upper-level jet’s secondary streak, leading to a persistent, severe event. The enhanced secondary jet streak appears only for developing systems that lead to extreme impact, as shown by 40 years of knowledge of late-spring severe blizzards over the area. It is shown that actual regional high-resolution models are able to represent the occurrence and the mechanism of late-spring severe blizzard events, thus increasing the confidence on their ability to represent current and future climate extreme variability. Understanding the preconditioning of dynamic and thermodynamic processes indicated by this analysis could be useful in supporting the operational forecast analysis.
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