DISCUSSION: As very strong thunderstorms erupted over the weekend across parts of Central Italy such as this shot of a very majestic storm in Ancona, Italy! These storms were a consequence of very robust and efficient moisture transport associated with a tropical low-pressure system (which formed over the Northern Adriatic Sea). This low-pressure system dramatically increased the amount of convective instability across much of East-Central Italy as well as the amount of vertical wind shear. The combination of the enhanced convective instability and the more pronounced wind shear acted to created an environment conducive for the development of severe thunderstorms. As observed in the image below (courtesy of Gianfranco Petraccini), there was a classic shelf cloud structure associated with the evolution of this particular severe thunderstorm moving ashore from over a small bay located just to the east of Ancona, Italy.
Shelf clouds form as a result of cooler outflow from the outer portions of strong to severe thunderstorms being forced to rise up and over warmer air downstream (i.e., in this case to the west of incoming severe thunderstorm coming in from east-to-west off the Northern Adriatic Sea). When the aforementioned process is coupled with additional large plumes of warm/moist air coming into eastern portions of the Italian Peninsula, this facilitates the development of thunderstorm-based structures such as this shelf cloud observed just two days ago in Ancona, Italy! To learn more about other high-impact weather events from across Europe, be sure to click here!