Agenzia Regionale per la Protezione dell'Ambiente del Friuli Venezia Giulia, Osservatorio Meteorologico Regionale
On March 26 2001 a tornado was observed on the Friuli plane (Northeastern Italy), close to the foothills. The event took place in the afternoon, 15:45 UTC and it lasted for about 15 minutes, fortunately no significant damages and injuries have been recorded since the tornado interested an uninhabited area with poor vegetation and cultivation due to the season.
The whole event was observed by some witnesses at a distance of about 1 km, from the tornado onset to its end, some photos of the funnel cloud are available. The reports of the observers, they are amateur severe storms chasers, were of great value for the study of the event.
In this work we analyze the environment where the tornado developed, zooming from the synoptic scale down to the local scale. Satellite images, lightning records, radio soundings data and information from the local network of automatic meteorological stations are involved in this study together with reflectivity and Doppler radar data. The presence of a supercell has been investigated in detail by means of radar reflectivity maps and the cyclonic circulation showed by Doppler radar images. A comparison among this case study and other tornado events occurred in our region has been carried out. Even if there are some similarities, this case shows some features not observed before probably because it happened very early in spring and that is unusual for Friuli region. The role of the orography on the onset of this event is explored and a thermodynamic analysis of the vertical profile of the atmosphere just before and after the tornado is presented.
A search has been done for a prognostic signature in the forecasting tools, those routinely are used at the OSMER; this search leads to some interesting consideration on the reliability of tornadoes forecasts in Friuli region.