Study of The Tornadic Event in The Plain of Caserta (Campania Region, Italy) On March 12, 2018: Radar-Observations And Numerical Simulations

On 12 March 2018, an EF2 tornado occurred in the southern urban area of Caserta city, causing eight injuries and relevant damages on buildings, cars and road infrastructure, amounting to several millions of euros. This study is focused on the description of the evolution of the tornadic supercell through X-band single-polarization reflectivity measurements, provided by the WR-10X weather radar operating Naples urban area. Moreover, this work investigates the synoptic and mesoscale processes that triggered the supercell, using the Weather Research and Forecasting (WRF) model. In WR-10X reflectivity volumes, the convective cell responsible for the tornadic event showed its first signature at 16:30 UTC, 65 km northwest of Caserta, near the Ausoni-Aurunci Mountains (Gulf of Gaeta). After that, the cell moved southeasterly with an estimated average translation velocity of 13 m/s. From 17:40 UTC, according to the reflectivity data measured at lower antenna elevations, a gradual transition of thunderstorm structure into a supercell has been observed. At 17:50 UTC, the reflectivity echo along the leading edge of the thunderstorm shows a clear Forward Flank Notch (FFN) signature, associated to a vigorous updraft, which caused a deflection of upper level winds around the core of the storm. The supercell crossed the neighborhood of Caserta at 18:00 UTC, showing a classic "hook-echo" signature in the region of cyclonic rotation (which supports the tornado formation). The Range Height Indicator (RHI) scan reveals that the s upercell had two distinct downdrafts, the Forward-Flank Downdraft (FFD), which is located in the leading part of the supercell, and the Rear-Flank Downdraft (RFD). The presence of the mesocyclone was also associated with a bounded weak echo region (BWER), a vertical channel of weak radar echo, related to a very strong updraft. A dedicated WRF simulation at very high resolution (1 km) over the Campania Region has been performed, using the WRF version 4.0 and a two-way nesting configuration among three domains. Preliminary results figure out a significant vertical wind shear and a high amount of water vapor at lower levels in the neighborhood of Caserta. These factors, together with a positive Potential Vorticity anomaly in the upper troposphere, may have supported the formation of the observed supercell. Merging data from X-band radar observations and WRF simulations proved to effeciently describe the fine structure associated to the anomalous tornadic event.