Storm Forecast
Valid: Thu 11 Aug 2016 06:00 to Fri 12 Aug 2016 06:00 UTC
Issued: Wed 10 Aug 2016 22:53
Forecaster: GATZEN

A level 1 was issued for central Italy, the central Balkans, Bulgaria, and Romania mainly for large hail and to a lesser extend excessive precipitation and severe wind gusts.

A level 1 was issued for western Russia into the central Ukraine mainly for large hail, severe wind gusts, and excessive precipitation.

A level 1 was issued for northern Algeria and Tunisia mainly for large hail and severe wind gusts.

SYNOPSIS

High amplified trough across central Europe moves slowly eastward, leaving a weak mid-level trough behind that extends into the southern Iberian Peninsula. Ridging takes place over western Europe. Cool air masses continue to spread into eastern Europe in the wake of an extensive frontal boundary from north-western Russia to the central Balkans and further into the central and south-west Mediterranean. Dry low-level air limits the potential of storms in the wake of this front. Best potential will be the region affected by the intense vort-max of the trough axis moving east across Sweden and the southern Baltic Sea region. More storms are expected especially with the southern portions of the colf front that moves south-east slowly over Italy and the Balkans. Moist low-level air and modest lapse rates are expected and storms are forecast to initiate where the frontal lift interacts with local sea breeze and mountain circulations.

DISCUSSION

Central Italy, central Balkans into Bulgaria and Romania

The frontal zone will affect this area and moves slowly south-east. Quite good low-level moisture is indicated by latest soundings and model data. This could allow for about 1000 J/kg CAPE as it overlaps with steeper lapse rates. Lift from mountain- and sea-breeze convergences will interact with the cold front and storms are forecast to re-intensify in the morning and noon hours. With strong deep layer vertical wind shear of 20 m/s in the lowest 6 km, storms are expected to be well-organized, and multicells and supercells are forecast. These storms may be capable of producing large hail. Furthermore, storms may ride the frontal boundary for some time and could produce excessive precipitation. Clusters of storms along the frontal boundary are expected later on and can move east. Some severe wind events are not ruled out along their leading gust fronts. Late in the period, convective activity is forecast to weaken.

Western Russia into central Ukraine

Ahead of the cold front, rich low-level moisture and modest lapse rates are present, and CAPE can exceed 1000 J/kg during the day. Late in the day, approaching cold front will support initiation of storms. Although vertical wind shear is limited, some well-organized multicells and mesocyclones are forecast, capable of producing large hail, severe wind gusts, and excessive precipitation. Clusters of storms are expected in the night hours that will weaken later on.

Northern Algeria and Tunisia

Mid-level trough will enter the region from the north. Some lift is expected reducing the capping inversion of the well-developed elevated mixtd layer. Over the Atlas mountains, intiation is expected during the day. With strong vertical wind shear, severe thunderstorms are possible, capable of producing large hail and severe wind gusts.