CONVECTIVE FORECAST
VALID Wed 24 Aug 06:00 - Thu 25 Aug 06:00 2005 (UTC)
ISSUED: 23 Aug 22:36 (UTC)
FORECASTER: GATZEN

There is a slight risk of severe thunderstorms forecast across SWrn Black Sea region

SYNOPSIS

Blocking high remains over NErn Europe. At its SWrn flank ... a cut-off low moves NE-ward into western Ukraine. To the west ... intense upper trough over NErn Atlantic expands into British Isles and North Sea. Associated cyclogenesis is expected north of Britsh Isles. At lower levels ... warm and unstable airmass is expected east of the cut-off low in western Black Sea region.

DISCUSSION

...Western Black Sea region ...
From northern Greece to Romania ... latest soundings show steep low-level lapse rates and rich low-level moisture ... yielding CAPE in the range of 700 J/kg. This airmass is expected to spread eastward in the range of occluded frontal boundary as indicated by latest model output. Aloft ... upper short-wave trough/vort-max is forecast to move northward over Black Sea region ... leading to QG forcing. On Wednesday ... frontal boundary is expected over western Black Sea ... and clouds with embedded showers should inhibit strong diurnal heating. CAPE should be sufficient for widespread convective activity, though. Thunderstorms that form will have a slight chance of being organized given around 20 m/s DLS underneath upper jet streak at SErn flank of the cut-off low ... and multicells/ supercells are expected ... capable of producing severe wind gusts, intense precip and large hail. Although LCL heights should be low ... chance for tornadoes is expected to be weak ... as LLS should remain weak. To the north ... thunderstorms are expected to form from Romania and Serbia to central Poland. Weak vertical wind shear should limit severe threat. Slow moving thunderstorms will pose a threat for local flash flooding, though.

...Central Mediterranean ...
Another short-wave trough/vort-max is forecast at the southern flank of the cut-off low ... that should affect northern and central Mediterranean. Moist low-level airmass and relatively steep lapse rates (CAPE of several 100 J/kg) are present over central Mediterranean ... and diurnal insolation should lead to sufficient instability over Italy and surrounding isles. QG forcing due to DCVA in the range of the upper vort-max as well as mesoscale forcing in the the range of sea breeze fronts should lead to thunderstorms during the day. As DLS will remain weak ... thunderstorms should be non-severe over most of the region ... and local flash flooding should be the most significant threat.

...British Isles ...
Intense cyclogenesis is expected north of British Isles. A cold front should move eastward during the morning hours. Although warm airmass is forecast to be stable ... strong low-level forcing and strong vertical wind shear may be sufficent for isolated shallow mesocyclones ... capable of producing severe wind gusts and a brief tornado or two. To the west ... upper vort-max propagates eastward over Ireland later in the period. Enhanced vertical wind shear is expected ... and thunderstorms that are expected to form may organize into multicells. Severe wind gusts and isolated hail should be the main threat.

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