Storm Forecast
Valid: Fri 10 Sep 2010 06:00 to Sat 11 Sep 2010 06:00 UTC
Issued: Thu 09 Sep 2010 16:52
Forecaster: TUSCHY

A level 1 was issued for areas S/SE of the Alps mainly for isolated large hail and heavy rainfall.

A level 1 offshore also includes the risk for waterspout reports.

SYNOPSIS and DISCUSSION

A negative tilted trough is placed over central Europe. Another impulse dives southeastwards along its western fringe, resulting in further amplification and a closed high-level circulation evolves over the central Mediterranean, as pool of low geopotential heights starts to drop off that trough. This feature then meanders over the central Mediterranean during the forecast with a gradual shift to the S/SE. Beneath this upper low, shear weakens significantly, so bulk shear values decrease below discerning levels for organized storms. Scattered to widespread thunderstorm activity is forecast with pulsating storms / a few organized multicells. The following hazards are expected:

- CAA atop warm SSTs increases LL CAPE, so a few spouts are well possible along any more organized convergence zone in the meso-gamma/beta scale.

-a good amount of convectively enhanced rainfall amounts, as synoptic-scale feature only displays a slow movement. However, no real focus is seen to support a concentrated area of excessive rainfall amounts. Highest peaks may occur over central Italy and along the E-coast of the Adriatic Sea.

- if storms manage to develop along the N-Aegean Sea/Greece , better shear/CAPE overlap may assist in a few organized hail storms, but model solutions diverge significantly in respect of initiation. Main activity probably delays until Saturday. Also, parts of SW-Hungary may see some LL shear/CAPE overlap, although shear magnitude in model data my be modified by QPF maxima to the west. Despite all that, an isolated tornado event over Hungary remains possible.

- Strong and persistent isentropic lift affects areas SE of the Alps with locally high rainfall amounts possible. Some MUCAPE is forecast, which could indicate a chance for convectively enhanced rainfall amounts. However, no robust thunderstorm risk is seen right now, so we will exclude this hazard in our bulletin.

The rest of the areas in the broad level 1 may see a few strong to isolated severe storms with marginal to isolated large hail and heavy rainfall being the main risk.

...Ireland and Scotland after sunset...

A strong wave affects the area during the night. Marginal CAPE evolves as mid-levels cool down in an environment with up to 20 m/s SW-erly winds at 700 hPa. Strong wind gusts remain the main risk with showers/isolated thunderstorms.