CONVECTIVE FORECAST
VALID 06Z THU 02/12 - 06Z FRI 03/12 2004
ISSUED: 01/12 16:55Z
FORECASTER: GATZEN

There is a slight risk of severe thunderstorms forecast across Western and northwestern Mediterranean

General thunderstorms are forecast across southern Iberian Peninsula, western and northern Mediterranean, Adriatic, western Balkans

SYNOPSIS

Upper trough axis of amplified upper trough expands from northern Scandinavia to northwestern Africa ... yielding a deep SW-erly flow from the northern Sahara desert to central Mediterranean and further to eastern Europe. To the southeast of the associated frontal zone ... rather warm and moist airmass will be advected northeastward into southeastern Europe.

DISCUSSION

...Western and northern Mediterranean ...
Well developed upper jet will affect western and northern Mediterranean on Thursday ... where deep vertical wind shear should likely reach more than 20 m/s. The airmass southeast of associated frontal zone is characterized by relatively steep lapse rates above the boundary layer and some low-level moisture ... yielding CAPE values up to 200 J/kg as indicated by latest ascends. GFS model output suggests some instability over the western and northern Mediterranean during the forecast period ... and current thinking is that some 100 J/kg CAPE may be possible on Thursday. During the day ... WAA is forecast from the Balearic Islands to extremely southern France and from central Italy to western Black Sea ... and QG forcing is expected due to some upper short-wave troughs moving NE-ward. Showers and thunderstorms should develop over the western Mediterranean and over the Adriatic ... moving NE-ward into northern Mediterranean, and western Balkans. Deep vertical wind shear seems to be adequate for very isolated organized convection over the Adriatic and western Balkans. To the west ... backing SE-erly surface winds over the western Mediterranean will lead to increasing SRH values during the period ... and chance for supercells should be significantly enhanced. Supercells that form will be capable of producing isolated large hail and severe wind gusts. As low-level SRH will be quite high in the WAA regime ... with more than 100 m²/s² locally ... and LCL heights will be low due to latest GFS model run ... a few tornadoes are expected. As QG forcing should continue during the night hours ... thunderstorms may merge into a MCS reaching southern France and northwestern Italy on early Friday. Intense precipitation and strong wind gusts should be the main threat.

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