Storm Forecast
Valid: Fri 03 Sep 2010 06:00 to Sat 04 Sep 2010 06:00 UTC
Issued: Thu 02 Sep 2010 17:50
Forecaster: TUSCHY

A level 2 was issued for parts of Tunisia, the Tyrrhenian Sea, Sicily and S-Italy mainly for excessive rainfall amounts, large to giant hail, severe to damaging wind gusts and tornadoes.

A level 1 surrounds the level 2 with a limited severe risk.

SYNOPSIS

Omega pattern over Europe persists. A weakening trough traverses the western/central Mediterranean and sparks numerous organized thunderstorms over the highlighted area. A few non-severe storms are forecast over far NE-Europe and along the coast of NE-Germany.

DISCUSSION

... N-Tunisia, Sicily, S-Italy and the Tyrrhenian Sea ...

A weakening upper trough affects the area during the forecast. This feature becomes absorbed by an extensive upper vortex to the north, so forcing weakens betimes.

A pool of extremely moist air is present south of Sicily, which advects northwards. As the upper wave draws near, surface pressure drops constantly and a LLJ evolves to its east, e.g. over Sicily. A sharp baroclinic zone is present with capped 3000 J/kg MLCAPE to its south and weakly capped 1000-2000 J/kg MLCAPE to its north. Persistent influx of high moisture content from the south beneath PVA maximum yield a favorable set-up for long-lived and large thunderstorm clusters with an excessive rainfall risk over a broad area. Life-threatening rainfall amounts beneath training/slow moving storms are forecast in a very efficient environment for prolific rainfall producers.

Further to the south, where CIN increases, more discrete storm structures are forecast with giant hail, tornadoes and damaging wind gusts. Storm coverage becomes more isolated in nature, but either discrete storms or a "tail-end charlie" (if a V-shaped cluster evolves) could produce extremely severe events.

The exact path of highest rainfall amounts remains quite unclear, as models have significant problems in handling the amount of latent heat release/convection. Hence, the level 2 still remains coarse.

...Ireland...

Slowly eastward propagating cold front affects Ireland during the night. A few storms are possible and moist inflow may assist in a few storms with heavy rainfall, but core of LLJ shifts rapidly to the north, so no focused severe risk is forecast for now. Nevertheless, conditions are prime for potentially backbuilding clusters west of Ireland. If this line builds far enough to the south, a level 1 may be issued for locally heavy rainfall amounts.