Storm Forecast
Valid: Thu 10 Jul 2014 06:00 to Fri 11 Jul 2014 06:00 UTC
Issued: Thu 10 Jul 2014 06:08
Forecaster: GATZEN

A level 2 was issued for parts of central Germany and Poland mainly for excessive precipitation.

A level 1 was issued for eastern France, Benelux, central and northern Germany, and central Poland mainly for excessive precipitation and to a lower extend tornadoes, large hail, and severe wind gusts.

A level 1 was issued for Romania and surroundings mainly for large hail, tornadoes, severe windcgusts and excessive precipitation.

A level 1 was issued for the Adriatic region mainly for large hail and excessive precipitation.

A level 1 was issued for the Baltic States into western Russia mainly for large hail and excessive precipitation.

SYNOPSIS

The south-European trough centred over Italy starts to move east and will be located across the Balkan Peninsula on Friday morning. A strong jet streak at its southern flank spreads into the Aegean region. To the north of the trough, a tongue of moist air is present over central Europe.

DISCUSSION

Romania and surroundings

A moist air mass is present across Romania and eastern Bulgaria. Overlapping with steep lapse rates spreading northward ahead of the approaching trough, CAPE of 1000 J/kg is expected in the afternoon and evening hours. Focus of initiation will be the Carpathians in the noon and afternoon, where upslope flow is forecast. However, intensifying QG forcing ahead of a short-wave trough as well as frontogenetical lift ahead of the approaching cold front may help for more widespread activity later on, starting over northern Serbia.

Deep layer vertical wind shear will increase from the south, exceeding 20 m/s, and supercells are possible, capable of producing large hail and severe wind gusts. Due to limited low-level buoyancy and vertical wind shear, tornadoes seem to be not the dominant threat, but a few isolated events are not ruled out, especially when isolated supercells form.

Storms are expected to merge into one or two MCSs spreading north-east, with severe winds and excessive rain the main threat.

Italy and Adriatic into western Balkans

The base of the European trough slowly moves east during the day, associated with strong QG lift as indicated by Q-vector divergence. Main focus will be a tongue of warm air over the southern Adriatic. Low-level air is still quite moist in the wake of the cold front, while lapse rates can improve near the trough centre due to diurnal heating and rather colds mid levels. Thunderstorms are currently observed across central Italy and will continue to spread south-east in the next hours.

Storms near the base of the trough will be weakly organized due to weak vertical wind shear. Clusters of storms are forecast with a limited potential of severe weather. Main threat seems to be excessive precipitation over the Adriatic area with highest coverage of storms. However, better organized storms may be possible in the southern portions where deep layer vertical wind shear is stronger. Supercells and multicells may produce large hail and severe wind gusts, and even tornadoes are not ruled out due to 10 m/s low-level vertical wind shear. During the night hours, storms will gradually weaken in the wake of the trough.

Southern Poland, central Germany, Benelux, eastern France, and surroundings

Along the well-developed warm front at the northern flank of the cut-off low, very moist air is still present. Diurnal heating north of the warm front will again lead to widespread initiation of storms in the noon and afternoon hours.

Strong moisture flux convergence is expected over the Benelux countries during the day, with a 0-1 km mixing ratio near 14 g/kg. Storms moving nearly parallel to the low-level convergence zone and rather slow storm motion will increase the potential of excessive precipitation. Large hail and local severe wind gusts are not ruled out.

Further east, low-level vertical wind shear increases, and a few tornadoes may form over central and eastern Germany as well as central Poland during the afternoon hours due to strong low-level buoyancy. Main focus will be outflow-boundaries of previous storms. Additionally, storms moving nearly parallel to the warm front over central Germany and central Poland will again pose a threat of excessive rain.

Baltic States into western Russia

Ahead of an approaching cut-off low and cold front, a tongue of moist air mass will spread southward. Initiation is expected in this air mass during the day. Weak vertical wind shear will limit severe potential, but a few hail and wind events are not ruled out, as well as excessive precipitation. Dry air advection from the north will be associated with weakening storms in the afternoon.