Meteorological Physical Background
The situation was determined by the passage of a cold front accompanied by severe pre-frontal convection.
The prefrontal convection was additionally enforced due to orographic
effects combined with a continuous flow of moist air from SW
(from the Adriatic), strong instability and wind shear in the lower atmosphere.
Bands of quasi-stationary prefrontal convection were responsible for locally ~ 400 mm of rain within 12 hours.
Mechanisms leading to these local maxima are still under investigation. Preliminary findings point out the occurrence of cold pools, pushed against the steep orography,
and dynamical low-level wind convergence around complex topography.
Based on the operational ALADIN/SI model, PEPS and other LAM guidance, flashflood warnings were issued by the Weather service, although the actual amount of rain surpassed
the expectations by factor 3-4.
Large variability of the rainfall characterized this situation. Temporal variability observed at a couple of rain-gauges only 30 km
apart and radar data indicated that many singular storm cells occurred and were then transported in the direction of the mean wind.
The spatial distribution of total observed rainfall probably does no justice to the variability due to too few observing stations.
Please, look at the basics describtions in SatManu: