Dynamical and microphysical properties of high impact orographic mesoscale convective systems from high resolution operational multiple-Doppler and polarimetric radar data

During the fall season, the southeastern region of France is often affected by intense flash-flooding episodes ensuing from the formation of quasi-stationary mesoscale convective systems along the south-eastern flank of the Massif Central Mountains. The precipitation efficiency in this region being very high, these systems can generate considerable amount of precipitation in relatively short periods of time. A well-known example of such systems is the so called “Gard case” (2002) during which 800 mm of rainfall fell down in less than 24 hours near Nîmes, resulting in many fatalities and total damage amount of about 1.2 billion US dollars.

Observing and understanding the dynamical and microphysical processes at play during these high impact weather events is critical to develop effective flood warnings systems and to improve their forecast. With this respect, the French Weather Service will soon start to provide forecasters and researchers with real-time, 3D multiple-Doppler winds and 2D hydrometeor fields inferred from the analysis of polarimetric and Doppler data collected by a sub-network of 6 operational C- and S-band radar systems in southern France. This paper proposes to describe the methods used to generate such products in regions of complex terrain, as well as to evaluate wind and microphysical retrieval performed during two successive intense hail producing weather systems that hit the Nîmes area on 20-22 October 2008.