CONVECTIVE FORECAST
VALID 06Z FRI 06/08 - 06Z SAT 07/08 2004
ISSUED: 05/08 13:12Z
FORECASTER: GATZEN

General thunderstorms are forecast across central Mediterranean, Balkans, SErn Europe, Alpine region, eastern France, western Germany, Benelux, eastern England, northern Scandinavia, western Russia

SYNOPSIS

Weak upper ridge will remain over Europe, while westerly jet continues over the Mediterranean. Embedded short-wave trough cuts off from northern Atlantic long-wave trough and merges to the upper cut-off low over SErn Europe.

DISCUSSION

...Central Mediterranean, Balkans...
Upper short-wave trough will propagate eastward reaching Greece during Friday. A 25 m/s jet streak is expected at the 300 hPa level from Tunisia to western Greece by Friday 12Z. Latest model output suggests weak DCVA and WAA ahead of this feature resulting in QG forcing. Affected airmass will be unstable with CAPE up to 1000 J/kg as indicated by GFS ... however ... low-level moisture seems to be quite shallow as indicated by Thursday's soundings. Relatively weak forcing ... and mentioned uncertainty of instability ... seems to inhibit widespread deep convection. If thunderstorms will form ... rather strong (15-20 m/s) 0-6km vertical wind shear should be adequate for organized convection over the Mediterranean. Isolated multicells/supercells are forecast initially forming along outflow boundaries of Thursday's convection and/or over land masses due to strong insolation and orographic support. Thunderstorm activity should spread northeastward into central Balkans as upper forcing should spread northeastward during the day. Decreasing vertical wind shear to the north limits severe potential. However ... isolated strong instability may be favorable for supercells. Any supercell that forms will be capable of producing large hail and strong wind gusts. Rather high LCLs and weak low-level wind shear do not indicate a significant threat of tornadoes ATTM. During the night ... thunderstorms may merge into one of two MCS over Romania/Bulgaria due to remaining QG forcing.

...Eastern France, western Alpine region, western Germany, Benelux...
Underneath the upper level ridge axis ... axis of warm/unstable airmass affects the region. A surface low/convergence line is forecast by latest model output that should lead to synoptic forcing. Thunderstorms are forecast during the day. Due to daytime heating ... instability should be moderate and CAPE is expected to reach 1500 J/kg locally. Weak vertical wind shear and weak forcing will not support organized thunderstorms. However ... isolated large hail and strong wind gusts and intense precipitation are not ruled out. Convection should cluster after cold pool formation later on.

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