A Climatology of the Mesoscale Environment Associated with Heavily Precipitating Events over a Northwestern Mediterranean Area

Heavily precipitating events (HPEs) over the northwestern Mediterranean, particularly affecting regions like the Causses and Cévennes, are driven by common mesoscale features such as slowly evolving trough-ridge patterns and diffluent midlevel flow. These events, characterized by daily precipitation exceeding 150 mm during autumn, show that instability and moisture are transported toward the target area via a low-level jet (LLJ) originating from the Mediterranean Sea. Strong moisture convergence occurs within the left exit of the LLJ, with parameters peaking during the mature stage. Clockwise rotation of low-level winds is observed throughout the event's lifecycle. However, synoptic and mesoscale patterns vary significantly depending on the location of precipitation, with differences in LLJ direction (southeasterly to southwesterly), midlevel flow orientation, and stretching of high moisture and instability areas. Long-lasting HPEs are associated with more pronounced quasi-stationary trough-ridge patterns, higher CAPE values, wetter tropospheres, and faster LLJs. The study utilized a 5-year climatological approach based on 3D-Var mesoscale analyses to document these features across four subdomains: Languedoc-Roussillon, Cévennes-Vivarais, South Alps, and Corsica.

Ricard, D., Ducrocq, V., & Auger, L. (2012). A Climatology of the Mesoscale Environment Associated with Heavily Precipitating Events over a Northwestern Mediterranean Area. Journal of Applied Meteorology and Climatology, 51(3), 468–488. https://doi.org/10.1175/jamc-d-11-017.1