Storm Forecast
Valid: Sun 04 Apr 2010 06:00 to Mon 05 Apr 2010 06:00 UTC
Issued: Sat 03 Apr 2010 20:20
Forecaster: SCHLENCZEK
A level 1 was issued for Corsica, central Italy, Slovenia and W Croatia for severe wind gusts, excessive rainfall, large hail and tornadoes.
SYNOPSIS
An upper trough over western Europe will lead to unsettled conditions over large portions of western-central Europe and the north-central Mediterranean. Most of the convection will occur in cold polar air near the trough axis. At the southern tip of the trough, cyclogenesis is forecast over the Gulf of Genoa. The resultant 1010 hPa surface low may become the focus for a severe weather episode in northern Italy as unstable air will be present in an environment with strong shear and SRH.
Stable conditions will prevail over SW Europe and most parts of eastern Europe where high pressure will dominate. In the second half of the forecast period, a large cyclonic vortex approaches the British Isles from the southwest, leading to strong to severe gusts due to an intense gradient flow.
DISCUSSION
...Corsica, central Italy, Slovenia, Croatia...
Ahead of the developing surface low, warm and moist air is advected into N Italy which will result in about 500 J/kg MLCAPE. As the upper shortwave trough approaches Corsica in the early afternoon, strong QG forcing will lead to convective initiation. Storms may profit from intense 20 - 25 m/s deep layer shear, enhanced 150 - 250 mē/sē SRH3 and strong LL winds. At this moment it seems most likely that a bowing line and / or isolated supercells will develop, posing a threat of severe wind gusts, large hail and a possible tornado.
In the late evening / night hours, storms will move eastwards towards Slovenia / Croatia and tend to merge into one or two MCSes with severe wind gusts and excessive rainfall being the main threat.
...France, Benelux countries, NW-central Germany...
Near the upper cold core of the trough, steep mid level lapse rates and diurnal heating will lead to a few hundred J/kg CAPE. LL shear and SRH3 are locally augmented and 10 - 15 m/s deep layer shear should be sufficient for some briefly organised multicells. Storms may be accompanied by marginally severe hail and strong wind gusts. After sunset, thunderstorm activity will diminish as CAPE vanishes.
