Storm Forecast
Valid: Wed 01 Apr 2009 06:00 to Thu 02 Apr 2009 06:00 UTC
Issued: Tue 31 Mar 2009 21:24
Forecaster: PUCIK

SYNOPSIS

An area of mid-level high pressure system with center over the Northern Sea will stretch from Atlantic to Central Europe and then curve to
SE Europe. This "channel" of high geopotential heights will separate the short-wave trough which is expected to deepen when moving from Scandinavia to NE Europe and a broad mid-level cut off low, placed over the W. Mediterranean. A warm advection will be well-established ahead of this low with weak cold front which will start affecting Italy by 12Z. Under the exit region of the jet, in association with strong QG forcing at mid-levels, slight cyclogenesis will be induced in the range of the frontal zone.


DISCUSSION

.... Sicily, Central Italy ...

The combination of advection of warm, humid airmass and strong synoptic-scale lift ahead of the advancing mid-level impulse should result in the release of latent instability, with MLCAPEs reaching several hundred of J/kg. Strong mid and upper level flow will increase the values of DLS to more than 20 m/s with shear in the lowest 3 kms staying in order of 10 - 15 m/s. As a surface trough is expected to develop with several small pressure centres confined to the cold front, slightly enhanced SREH values will build up over the island of Sicily by 12Z ( Per several GFS runs, only around 100 - 150 J/kg will be available to the developing storms). Convergence on the frontal zone should lead to the initation of thunderstorms, which will affect the area between 09 and 18Z. Due to the favourable wind-shear conditions, thunderstorms should be well organized, probably of multicellular nature, oriented along the progressing front. Threat of marginally severe hail is anticipated, especially if isolated cells manage to develop, with supercellular characteristics. One of the limiting factors for hail, however, will be the relatively little CAPE to be tapped by the storms as well as the lack of isolated cells ahead of the front. The greatest threat over Italy will last from 09 to 12Z, over the Sicily from 12 to 18Z.