CONVECTIVE FORECAST
VALID 09Z FRI 17/10 - 06Z SAT 18/10 2003
ISSUED: 17/10 08:53Z
FORECASTER: GATZEN

There is a moderate risk of severe thunderstorms forecast across parts of the central and western Mediterranean

There is a slight risk of severe thunderstorms forecast across over the western and central Mediterranean

General thunderstorms are forecast across over most of the Mediterranean

SYNOPSIS

Blocking upper ridge placed over the North Sea. It will weaken as cold arctic outbreak is forecast over northern Europe. South of the blocking ridge ... relatively strong southern jet overflows the Mediterranean. Embedded short-wave trough over the southern Iberian Peninsula will move across the western Mediterranean in a negatively tilted way, and intense cyclogenesis is forecast. South of the short wave ... upper jet streak over northern Africa spreads into the central Mediterranean.

DISCUSSION

...Western and central Mediterranean...
Latest water vapor satellite image indicates a strong SWerly jet streak over northwestern Africa. This jet streak is expected over the central Mediterranean at the end of the forecast periode. East of the associated short wave trough over the Iberian Peninsula ... strong WAA has set in over the western and central Mediterranean, and mid level clouds can be seen on latest visible satellite image. Sounding over Tunis shows a mixed airmass above the capping inversion at 850 hPa and a relatively moist boundary layer, yielding CAPE values up to 700 J/kg. North and west of this unstable airmass ... soundings indicate a convectively mixed airmass over the Mediterranean. At the surface ... deepening low is forecast over the central western Mediterranean ... with a warm front reaching from southern Italy to Sardinia. As the surface low is expected to intensify during the forecast periode ... easterly surface winds should strengthen over the central Mediterranean and north of the warm front over the northwestern Mediterranean. During the forecast periode ... convective activity should go on over the western and central Mediterranean. Organized convection like multicells and bow echoes should form due to increasing forcing and strong deep layer shear, spreading eastward. High winds and high amounts of rain should be the main severe threat with this convection. However ... expecially over the southeastern parts of the affected region, supercells may form as low level SRH values will be relatively high and CAPE could reach more than 1000 J/kg in the afternoon. Large hail, strong wind gusts and tornadoes, some of them may be strong (>F2), will be possible with any supercell that forms.

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