CONVECTIVE FORECAST - UPDATE
VALID 22Z MON 25/08 - 06Z TUE 26/08 2003
ISSUED: 25/08 21:54Z
FORECASTER: GATZEN

There is a moderate risk of severe thunderstorms forecast across southern Italy, northern Sicily

There is a slight risk of severe thunderstorms forecast across central Mediterranean

General thunderstorms are forecast across Mediterranean, southeastern Europe

SYNOPSIS

As building upper ridge ATTM over the British Isles expands NWWD ... High-over-low block is forming over the central Atlantic ... Intense long wave trough with several vort maxima at its periphery is covering NE Europe. Weakly undulating zonal southern frontal zone is extending across the Mediterranean regions. During the next hours ... vort-max is forecast to migrate across the central Mediterranean.

DISCUSSION

...Central Mediterranean...
Vorticity- maximum is crossing the central Mediterranean ... reaching the Ionic Sea tomorrow morning. Strong convection has formed on late Monday and several MCS migrate eastward ATTM. Ahead of this feature ... WAA from the Sahara into the central Mediterranean continues. This airmass is characterized by steep lapse rates between 850 and 600hPa. Underneath the cap ... strong and deep moisture pooling results in very large CAPE values up to 5000 J/kg (LITC at 18 UTC). Expect that low level mixing will be marginal during the night ... and unusual warm water surface (30°C) is in place ... low level moisture should be preserved. Additionally, wind latest profiles suggest that mentioned vorticity maximum is accompanied by moderately strong mid-level winds ... yielding 0-6 km shear on the order of 40 knots. Under that conditions ... the MCS east of southern Italy should continue during the night, and is expected to cross southern Italy till tomorrow morning. This will be a particular dangerous situation ... giant hail is expected with this feature ... and severe winds will likely occur along the leading edge of the MCS. In the surrounding area of the main MCS ... new convective cells could initiate. As vertical shear will be moderate and large CAPE values are present, supercells may form. Giant hail, damaging wind gusts and tornados will be possible then.

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