Storm Forecast
Valid: Thu 29 Mar 2012 06:00 to Fri 30 Mar 2012 06:00 UTC
Issued: Wed 28 Mar 2012 20:11
Forecaster: GATZEN

A level 1 was issued for the northern Balkans mainly for large hail.

SYNOPSIS

A high is situated over north-western Europe. Polar troughs can move south-eastward over eastern Europe. Weak geopotential is also present over the west Mediterranean. While mostly dry polar air masses are expected over the eastern portions of Europe, better low-level moisture is likely along the frontal zone from the North Sea and France to the Balkans. Lapse rates will be rather weak.

DISCUSSION

Northern Balkans

Some potential of organized thunderstorms is forecast over the Balkans. Ahead of the approaching cold front situated over the northern Alps at noon, a westerly flow is expected by latest models. This may be associated with some moisture advection and moisture pooling to the south of the Alps and over the Balkans. Upslope flow over the western Balkans is expected to support this moisture pooling. Additionally, daytime heating of the rather cold air mass is expected to yield better lapse rates and some CAPE is forecast.

During the day, a trough axis is forecast to move south-eastward over the Alps and will affect the Balkans. Strong north-westerly mid-level winds are expected to reach 20 m/s over the Balkans, resulting in rather strong deep layer vertical wind shear of 20 m/s (0-6 km). Although the flow is rather complex, forcing will likely act on the air mass and models indicate height falls over the Balkans.

Current thinking is that the low-level forcing due to upslope flow and sea breeze fronts together with the main frontal zone will be strong enough to initiate thunderstorms. Limiting factor is the weak moisture, and later observations have to confirm the GFS/ECMWF moisture forecast. Thunderstorms will have a good potential to organize due to the deep layer vertical wind shear, and multicells are forecast. Larger hodographs may also turn out in the complex terrain and could support supercell development. As the wet bulb zero is low, and mid-level lapse rates will improve with the approach of the trough axis, these organized storms will pose a threat of severe hail in the afternoon and evening hours. The storms will likely decay during the night as instability rapidly decreases after sunset.