Storm Forecast
Valid: Wed 26 Jun 2013 06:00 to Thu 27 Jun 2013 06:00 UTC
Issued: Wed 26 Jun 2013 05:35
Forecaster: GATZEN

A level 1 was issued for eastern Romania and central Urkaine mainly for large hail and excessive precipitation.

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

A level 1 was issued for north-western Russia mainly for large hail.

SYNOPSIS

Two trough centres currently over the Alps and the North Sea will merge to a closed upper low across western central Europe today. This will be associated with weakening synoptic forcing across eastern central Europe today, and the frontal boundary will move eastward behind a frontal wave. Ahead of this frontal wave, warm and moist air masses will remain across south-eastern Scandinavia, whereas relatively dry low-level air masses will affect most of Europe. The cool air mass that dominates Europe is also associated with weak lapse rates due to mid-level subsidence. Steep lapse rates can be found in the wake of the Alps across northern Italy as well as over the high terrain of the Iberian Peninsula and Turkey.

DISCUSSION

Eastern Romania into Ukraine and Belarus

A tongue of moist and warm air is present ahead of the cold front that continues eastward today. Thunderstorms will go on across Bulgaria and Romania and will spread further north-east into the Ukraine. Although lapse rates are rather weak, at least 1000 J/kg CAPE is expected. Vertical wind shear is weak but increases near the cold front reaching about 10 m/s in the lowest 3 km. This allows for slightly better organized storms capable of producing large hail. Storm motion parallel to the frontal boundary will also be associated in a threat of excessive precipitation. Overall threat is expected to be rather limited.

Southern Baltic States

The frontal wave that affected Poland on Tuesday has reached the southern Baltic Sea. It will further depart from the main frontal boundary as it moves north-westward. As a consequence, low-level convergence will decrease over most of east central Europe. With westerly winds, cold air advection will affect Poland. The prefrontal moist air mass will move northward affecting the southern Baltic States today.

Latest observations indicate surface dewpoints of 15-20°C and at least some insolation during the morning. Latest soundings indicate moist adiabatic profiles allowing for weak CAPE in response to low-level heating, and thunderstorms are forecast in the weakly-capped moist air mass starting in the late morning hours and spreading north-eastward ahead of the beginning cold air advection from the south-west. Especially near the Baltic Sea and Poland, deep layer vertical wind shear will be moderate today due to a mid-level jet streak. Consequently, some better organized storms are not ruled out, and multicells are forecast that can produce marginally severe hail and excessive precipitation. The threat increases later in the day as the low-level cold front moves away from the region with better deep layer vertical wind shear.

South-eastern Scandinavia into Russia

Moist-adiabatic lapse rates and rich low-level moisture together with diurnal heating will result in CAPE around 500-1000 J/kg across Finland and surroundings today. Weak forcing and vertical wind shear will limit the potential to produce severe weather. However, pulse storms are not ruled out and an isolated large hail or flash flood event is not ruled out.

Further south, better lapse rates can be found over Russia, where CAPE in the order of 2000 J/kg is expected. Despite weak vertical wind shear, chance of severe hail increases over this region due to pulse storms.

Italy

Thunderstorms have developed near the base of the southern centre of the European trough. Latest soundings indicate steep lapse rates between 850 and 750 hPa in the wake of the Alps that will spread southward during the day. Although low-level moisture is limited, diurnal heating and sea breeze convergence will likely allow for thunderstorms over northern and central Italy today. Given the weak vertical wind shear, storms are not expected to organize. Locally large hail is not ruled out, though.