Storm Forecast
Valid: Tue 30 Jul 2013 06:00 to Wed 31 Jul 2013 06:00 UTC
Issued: Mon 29 Jul 2013 23:11
Forecaster: GATZEN

A level 1 was issued for northern Greece and the southern Balkans into Bulgaria and Romania mainly for large hail and severe wind gusts.

A level 1 was issued for northern Romania, westen Ukraine and Belarus mainly for severe wind gusts and excessive precipitation.

A level 1 was issued for the Baltic States mainly for large hail, excessive precipitation, and tornadoes.

SYNOPSIS

A long-wave trough across north-western Europe spreads into Scandinavia. At its southern flank, a strong westerly jet streak spreads into Central Europe. Downstream, the intense negatively tilted short-wave trough weakens rapidly as it runs into the east-European ridge axis. At lower levels, a tongue of hot air is advected further east, but weakening lapse rates and rather dry low-level air across Belarus and the central Ukraine will limit instability. Cold air advection will dominate across the Mediterranean.

DISCUSSION

Northern Greece into the Balkans, Bulgaria and Romania

The tongue of hot air and steep low- to mid level lapse rates spreads eastward until the forecast period. It will become quite narrow as a fast moving cold front pushed east reaching a line from the central Balkans to eastern Poland at 06 UTC. To the east of the cold front, latest soundings indicate moderate boundary-layer moisture and only weak CAPE.

Over the Balkans and Greece as well as Bulgaria and most of Romania, cold air advection will set in from the northwest. However, steep lapse can remain for most of the day. Low-level moisture will be weak over most o the region. With the cold front, better moisture is advected from the west, but the cool airmass will be likely capped when it spreads below the plume of hot air.

Most storms will likely develop across Romania given best low-level convergence there. Further south, weak convergence along near the cold front is expected and storm coverage is forecast to be weaker. Given only weak vertical wind shear du to the rapidly decreasing winds at low and mid levels, storms will have a low potential to organize. Main threat is expected to be hail given the remaining steep lapse rates in the hail growth zone. Additionally, severe wind gusts may occur given the rather fast moving cold front and the deep boundary-layer at its eastern flank.

Northern Romania into the west Ukraine and Belarus

As the cold front moves into the high across eastern Europe, it slows down, while low-level convergence and moisture pooling increases. Therefore, rich boundary-layer moisture will result from northern Romania to the western Ukraine and Belarus into the southern Baltic States. However, it is questionable if rich moisture and step lapse rates will overlap, given the best moisture behind the cold front where lapse rates will be weak. To the east, rather weak boundary layer moisture will be associated with weak instability.

Current thinking is that a squall line can develop from northern Romania to the Baltic Sea near southern Finland during the afternoon and evening. Rather weak vertical wind shear is expected due to the rapidly decreasing low- and mid-level wind fields and degree of storm organization is expected to be low. Large hail is forecast with the stronger storms. Additionally, severe wind gusts are forecast given the deep boundary-layer ahead of the cold front. Limiting factor will be the rather slow movement of the cold front that becomes more parallel to the low-to mid level wind field. Due to the slow propagation, excessive rain is also not ruled out.

Baltic States

Better dynamics are forecast for the Baltic States at the northern nose of the warm air plume. Together with a low-level jet across the eastern Baltic Sea, 0-1 km low-level vertical wind shear will be around 7 m/s. Although the boundary-layer will be rather cold initially, diurnal heating may result in sufficient buoyancy and storms may develop into mesocyclones due to favorably veering profiles in the warm air advection regime. With this activity, a tornado cannot be ruled out across the Baltic States.