Severe hailstorm in northern Italy in June 2006.
25 May 2022
29 June 2006
By Agostino Manzato (OSMER ARPA-FVG) and Jochen Kerkmann (EUMETSAT)
As also happened in 2005, in 2006 the most interesting day in terms of severe thunderstorms and hail in the Region of Friuli-Venezia Giulia (Italy) was 29 June. The synoptic situation at 12:00 UTC (abs. topography at 500hPa) shows a trough with an axis that connects Denmark to Corsica such that Northern Italy is in a strong south-westerly flow.
The radiosounding of Udine (code 16044) indicates a wind of 83km/h at 500hPa and relatively high values of Lifted Index (-6K), Maximum Buoyancy (14K) and CAPE (1600J/kg). A time series of the radiosounding of Udine, including a plot of the available potential energy (CAPE, see red line), shows a deep layer of warm-moist air (Te > 340K) in the low layers at 12:00 UTC on 29 June.
It is believed that this low-level 'fuel' together with the forced lifting from an approaching tropopause dynamic anomaly (PV anomaly, see WV6.2 images with ECMWF analysis, Source: M. Putsay) triggered the intense thunderstorms over northern Italy, which formed the Mesoscale Convective System (MCS) that reached Hungary later on the same day (see case study two severe MCSs on the same day over Hungary).
The first severe thunderstorms had already developed in the morning in the Lombardy Region and quickly moved into the Veneto and later the Friuli Region. As in many other cases (see eg Meteosat-6 rapid scan images of severe hailstorm in northern Italy on 4 August 2002), the storms followed the southern slope of the Alpine Chain leaving a trail of destruction (wind and hail damage) in its wake.
Between 12:30 and 13:30 UTC the Province of Pordenone was particularly hard hit by strong wind gusts and a large number of roofs were blown off. A more detailed report (in italian language) is available here.
Both, updrafts and downdrafts were very strong in this case, as indicated by the convective outflow boundary (eg seen in the HRV image at 10:30 UTC), the high reflectance of about 6–7% in the IR3.9r channel (see RGB composite image below and 12:15 UTC 4-panel composite, source: M. Putsay) and, last but not least, by the large occurrence of hail.
Other satellite indicators for the severity of the storms are the overshooting tops, the gravity waves within the anvil top and the radial Cirrus seen in the HRV images.