Storm Forecast
Valid: Thu 14 Mar 2013 06:00 to Fri 15 Mar 2013 06:00 UTC
Issued: Wed 13 Mar 2013 22:33
Forecaster: GATZEN

A level 1 was issued for the southern Adriatic mainly for excessive precipitation.

A level 1 was issued for the southern Balkans, eastern Bulgaria and Romania mainly for large hail, tornadoes, and severe wind gusts.

SYNOPSIS

Unseasonably deep polar trough extends from northern Europe into the west Mediterranean. The southern centre of this trough will move eastward until Thursday morning and becomes a rapidly moving, negatively-tilted short-wave trough during the period. It will affect the southern Adriatic and the southern and eastern Balkans until Friday morning. Otherwise, very dry air masses will suppress deep moist convection across most places.

DISCUSSION

Southern Adriatic Sea to southern Balkans and Black Sea region

Ahead of the approaching short-wave trough, a tongue of warm air is advected into the Aegean Sea and Turkey. The warm air advection regime will also affect the Balkans east of an approaching cold front. Although the warm air mass is associated with rather poor lapse rates initially, strong QG lift is expected to lead to steep lapse rates especially near the cold front.

At low levels, relatively rich low-level moisture is already in place as indicated by latest soundings. Additionally, a tongue of rich boundary-layer moisture that spreads across the Aegean into Bulgaria is indicated by latest model forecasts. Together with moisture pooling across most of the warm air advection regime, around 6 g/kg mixing ratio will evolve according to latest GFS model run. This is expected to lead to CAPE in the order of 500 J/kg ahead of the cold front.

Current thinking is that thunderstorms will be located across the southern Adriatic in the morning hours and will gradually spread north-eastwards. Given the well-developed moist inflow from the south/south-east, linear convective systems along and east of the cold front that may affect some regions for quite some time. This may result in excessive precipitation and local flooding. Later in the period, convection is also expected further north due to the diurnal heating prior to the approaching trough. Especially these later storms will have a potential to organize into multicells and supercells as vertical wind shear is strong. Latest GFS indicates a bulk shear up to 35 m/s in the lowest 6 km, 25 m/s in the lowest 3 km and 15 m/s in the lowest 1 km. As a consequence, locally large hail, severe wind gusts and tornadoes are not ruled out. The overall threat is limited given the weak diurnal heating and limited low-level moisture. However, a level 1 seems to be warranted in this situation.

In the wake of the cold front, additional storms are forecast across the southern Adriatic region, but the weak vertical wind shear will limit the severe potential.