Storm Forecast
Valid: Wed 03 Aug 2011 06:00 to Thu 04 Aug 2011 06:00 UTC
Issued: Tue 02 Aug 2011 21:36
Forecaster: PUCIK

A level 1 was issued for Northern Italy and surroundings mainly for large hail, marginally severe wind gusts and to the lesser extent for excessive precipitation.

SYNOPSIS

At midlevels of troposphere, a filling trough is forecast to move across Western Europe, deamplifying and with weakening flow at its forward flank. The trough is a part of a large cyclonic vortex over Atlantic, which remains stagnant and centered to the southwest of Iceland. East of the trough a ridge will stretch from the Mediterranean, across parts of Central Europe to Scandinavia. On its forward flank a cut-off low, centered over Belarus around noon, will move to the southeast.

The best conditions for thundestorms will be observed to the east of a deformed surface frontal boundary, stretching across Western and Southwestern Europe on the forward flank of the trough. Even though large portions of Germany and France should see scattered thunderstorms during the day, severe threat should stay low or only marginal due to the unfavorable vertical wind profiles and unimpressive CAPE values. The best thermodynamic conditions will be present across the western Mediterranean, but due to the high CIN values, initiation is very unlikely.

DISCUSSION

... Northern Italy, extreme southern Switzerland and southwestern Austria ...

An overlap of moderate degree of instability, as agreed by GFS and ECMWF (values locally exceeding 1000 J/kg), is expected with slightly enhanced westerly flow aloft, resulting in 15-20 m/s of DLS. Wind should gradually strenghten with height, reaching around 25 m/s at 300 hPa with little directional shear in the lower levels. Initiation will be likely tied to the regional, topographically, induced convergence zones. Slight forcing should be available from the approaching trough, but no concentrated zone of strong lift is forecast. Well organised multicellular, including the possibility of a briefly supercellular, convection is forecast, with stronger storms posing threats of large hail and due to the slightly enhanced Theta-E values, also marginally severe wind gusts. Towards east, slower storm motion may also lead to some localised excessive precipitation event.