CONVECTIVE FORECAST
VALID 06Z SAT 06/09 - 06Z SUN 07/09 2003
ISSUED: 05/09 19:26Z
FORECASTER: DAHL

General thunderstorms are forecast across W central Europe.

General thunderstorms are forecast across the SW Mediterranean Regions.

SYNOPSIS

Large-scale upper ridge is covering central north and central Europe ... with a quasi-stationary elongated/extensive upper low present downstream over E Europe. Upstream ... shortwave troughs ATTM over the E Atlantic are progressing east/northeastwards ... affecting the W portions of the forecast area during the period. Weak southern upper frontal zone is stretching across the S Mediterranean.

DISCUSSION

...SW Mediterranean...
ATTM ... soundings across the Mediterranean are not available ... but numerical 850 hPa theta-e and SBCAPE analyses along with SFC OBS suggest that and an elevated mixed layer is present over the SW Mediterranean Sea atop SFC dewpoints on the order of 20°C ... supporting ample CAPE values. Though SFC-based moist layer may potentially be rather shallow ... current convective activity shows that low-level moisture is sufficient to maintain deep moist convection. Resultant decaying MCS may be ongoing over central Italy towards the beginning of the forecast period.

Steep lapse rates will likely reside over the SW Mediterranean ... and probably overspread extreme S Italy and S Sardinia during the afternoon. CAPEs may well be in the 1500 to 2500 J/kg range where EML is present. Though no distinct vort max is expected to cross the area ... low-level warm advection and lobes of DCVA as suggested by numerical model guidance may promote isolated TSTMS towards late afternoon/evening. It appears that CAPE and shear will be sufficient for severe thunderstorms ... primarily multicellular storms ... an isolated severe wind/hail event may occur. If storms happen to intercept hilly terrain over Sicily/Sardinia ... chances will be enhanced that updraft acquires rotation owing to local low-level flow perturbations/augmented SRH ... and brief tornado/very large hail threat would excist.

Refraining from SLGT owing to weak observational support underlying this scenario.

...Central Europe...
Ahead of vort max in weakly unstable air over central Europe ... TSTMS will likely form during the afternoon. Ahead of this vort/speed max ... isolated marginally SVR TSTMS could occur late in the evening ... if storms can be maintained against diurnal low-level stabilization ... which is becoming increasingly effective early in the evening. Later observational trends have to be awaited to specify SVR threat.

...East Europe and British Isles...
Same reasoning applying to the British Isles and to Belarus/Romania/Ukraine ... a few shallow TSTMS may occur beneath thermal trough axes rotating about the main upper low ... but CG strikes will likely be too isolated to warrant a gen thunder outlook over this area ATTM.

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