CONVECTIVE FORECAST
VALID 06Z WED 20/08 - 06Z THU 21/08 2003
ISSUED: 19/08 22:11Z
FORECASTER: DAHL

General thunderstorms are forecast across Iberia ... the Mediterranean ... E and NE Europe.

SYNOPSIS

Slightly meandering zonal upper flow extending across northern Europe ... with main upper s/w trough ATTM crossing S Scandinavia. Weak southern-stream vort maxima are crossing the Mediterranean regions. Main low-level frontal zone is expected to stretch from N France across Germany into NE Europe at the beginning of the period ... and is progged to make eastward progress only over NE Europe/W Russia ahead of the upper trough.

DISCUSSION

...Mediterranean...
Airmass across the Mediterranean appears to be characterized primarily by rather dry inverted-V type profiles. However ... LIRE 18Z ... LIPD 18Z and other ascents across the region indicate rather shallow SFC-based moist layer. Though this moisture should be mixed out with diurnal heating at most places ... MLCAPEs in the 2000 to 3000 J/kg could locally be realized where the cap can be maintained and trap SFC-based moisture beneath it. These profiles may be found especially across Italy ... W Balkan States and Greece. In response to insolation ... orographic forcing and DCVA-related ascent ahead of vort maxima progged to cross the region during the day ... widespread TSTMS should develop towards early afternoon across Italy and the Balkans. Large-scale shear will be rather weak ...with 15 to 20 knots at 500 hPa ... and given that the majority of the storms will likely develop in rather dry weak-CAPE environments ... allover organized severe weather threat appears to be rather low ... though very gusty winds will likely accompany the storms.

However ... N Italy and the N Adriatic Sea will likely see easterly low-level winds ... and chances exist that deep/rich moisture will locally be present. If storms develop in this environment with enhanced shear ... supercells could easily develop. If so ... localized threat of very large hail ... damaging wind gusts and a brief tornado or two exists. Small supercell threat also appears to exist over the Balkans into the Aegean Sea where orographically enhanced shear may promote updraft rotation if large CAPE values were realized. Threat appears to be quite conditional though ... thus refraining from SLGT ATTM.

...Iberia...
Dry environment will likely maintain downburst threat across the Iberian peninsula. Expect scattered high-based TSTMS to form during peak heating amidst weak DVCA regime. However ... given weak CAPE and weak shear ... organized severe threat appears to be rather low.

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