Storm Forecast
Valid: Wed 09 May 2007 06:00 to Thu 10 May 2007 06:00 UTC
Issued: Tue 08 May 2007 23:39
Forecaster: GATZEN

SYNOPSIS

Broad region of low geopotential covers northern Atlantic and Scandinavia. At the southern flank, a strong upper jet stream is directed towards British Isles and central Europe. An upper trough is embedded in the strong flow, propagating into eastern Europe during the period. A weak upper ridge follows over western Europe. Western Mediterranean is covered by a subtropic ridge, while upper cut-off low is present over south-eastern Mediterranean. At lower levels, cool air mass has spread into the northern half of Europe, while warm air is present over Mediterranean regions.

DISCUSSION

Northern Balkans, northern Adriatic, northern Italy

Well-developed European frontal boundary will remain quasi-stationary over northern Balkans, while embedded frontal waves propagate eastward. South of the Alps, a weak low is forecast to form over northern Adriatic region, providing some warm air advection over Balkans. In the range of the frontal boundary, latest models indicate rather rich low-level moisture, and air mass will likely destabilize during the day given some diurnal heating as well as some QG forcing in the range of the upper trough. Thunderstorms that form will be influenced by the strong vertical wind shear present in the range of the upper jet stream. Strong (30 m/s) deep layer vertical wind shear as well as favorable veering profiles (300-600 J/kg 0-3 km SRH) will be supportive for supercells. Large hail and severe wind gusts will be possible with every supercell that forms. Although low-level buoyancy will be relatively weak over most of the region, tornadoes are not excluded as 0-1 km vertical wind shear is relatively strong (10 m/s locally). Thunderstorms are expected to develop around noon, propagating south-eastward. After sunset, thunderstorms are forecast to weaken due to low-level stabilization.

For northern Italy, chance for severe thunderstorms is lower, but given strong DLS, a few mesocyclones are not excluded.

Northern/western Black Sea region

In the range of the base of propagating European trough, cold air mass spreads into Black Sea region. This cold air mass is getting deeper over the northern Black Sea region, and thunderstorms are expected to develop in the range of the trough center. Best potential for a few organized cells is expected near the Black Sea, where vertical wind shear increases. Multicells will likely be the main convective mode, capable of producing severe wind gusts hail. Especially along the cold front,
favorable veering profiles/rather high SRH values are possible, and mesocyclones are not excluded, capable of producing large hail. As low-level buoyancy is quite strong and low-level wind shear reach 10 m/s, a few tornadoes are also possible to develop.

Over western Black Sea region, frontal boundary becomes quasi-stationary. In the range of the front, rich low-level moisture and associated instability are likely to develop. Thunderstorms that form along the cold front may be severe given some low-level vertical wind shear near the cold front, and mesocyclones are not excluded. There will be a weak tornado threat given rather high low-level buoyancy and low-level SRH, and a few events are not excluded.