Storm Forecast
Valid: Thu 06 Sep 2012 06:00 to Fri 07 Sep 2012 06:00 UTC
Issued: Wed 05 Sep 2012 21:25
Forecaster: GATZEN

A level 1 was issued for the south-central Mediterranean and the central Balkans mainly for excessive precipitation and large hail.

A level 1 was issued for eastern Hungary, northern Romania, and western Ukraine mainly for large hail and excessive precipitation.

A level 1 wa issued for western central Norway mainly for severe wind gusts and tornadoes.

SYNOPSIS

A ridge is centred across western Europe. A north-westerly jet has evolved at its northern and eastern flank, and short-wave troughs are crossing Scandinavia and the Baltic States during the period. To the south of the ridge axis that extends from France to the Alps and the Black Sea, low mid-level geopotential covers southern Europe. At lower levels, cool air masses have entered central Europe behind a cold front that moves into eastern Europe, where warmer air masses and relatively steep lapse rates are still present. Across the central Mediterranean, lapse rates have decreased. Rich low-level moisture is observed across the Mediterranean Sea and the Black Sea.

DISCUSSION

Central Mediterranean

A rather strong mid-level jet streak moves eastward across the south Mediterranean Sea. It will be associated with increasing deep layer vertical wind shear at the southern part of the Mediterranean low pressure system. Thunderstorms that are expected to go on across the central Mediterranean are forecast to get better organized in the southern portions from southern Italy to the southern/central Balkans. Multicells and supercells may develop. These storms may be accompanied by large hail and excessive precipitation. The overall threat seems to be rather low, though.

Hungary and Romania to Ukraine

Along the cold front, thunderstorms are expected during the day. Given low-level moisture of 10 g/kg in the lowest kilometre and rather steep low-level lapse rates, MLCAPE might reach 1000 J/kg in the afternoon. Additionally, moderate vertical wind shear is expected that will be around 7 m/s bulk shear in the lowest 3 km. Some intense thunderstorms are forecast, capable of producing locally large hail and excessive precipitation. The threat is limited given the relatively weak thermodynamic profiles and low-level heating.

Scandinavia and Baltic States

Strong synoptic forcing is expected as an intense short-wave and associated strong jet streak will affect the region. However, it seems that the air mass will remain stable, and thunderstorms are not forecast. To the north of the main frontal zone, the maritime air mass may become unstable at the cyclonically sheared flank of the mid-level jet streak. These storms may be capable of producing severe wind gusts and tornadoes given strong low-level vertical wind shear exceeding 10 m/s in the lowest 3 km, and isolated events are not ruled out. Additionally, excessive precipitation is forecast along the Norwegian coasts, but the convective contribution is rather small so that a threat level is not introduced.