Storm Forecast
Valid: Tue 17 Jun 2014 06:00 to Wed 18 Jun 2014 06:00 UTC
Issued: Mon 16 Jun 2014 23:01
Forecaster: GATZEN

A level 2 was issued for southern Italy and Albania/Macedonia mainly for large hail, severe wind gusts.

A level 1 was issued for northern Tunisia, central and southern Italy, Adriatic and northern Ionian Sea, northern Greece and southern Balkans into Bulgaria, Romania and Moldova mainly for large hail and severe wind gusts.

A level 1 was issued for eastern Iberia and the Gulf of Valencia mainly for large hail and severe wind gusts.

SYNOPSIS

Atlantic high continues without a weakening tendency. Arctic air masses will spread into Scandinavia and western Russia at the eastern flank of this high. Polar air masses that have spread into most of Europe will warm in response to diurnal heating, and slightly decreasing moisture and lapse rates can be observed to the south-west of a new cold front that enters the Ukraine, Poland, and eastern Germany in the afternoon and evening hours. A few storms can develop especially below the axis of the long-wave trough from Germany across the Alps, southern France, into eastern Iberia.

Ahead of the long-wave trough, a west-south-westerly flow will establish from northern Tunisia to the Aegean and Black Sea region. An elevated mixed layer will spread into the east Mediterranean, affecting the Ionian and Aegean Sea. Weak frontogenesis to the south of Italy will additionally allow for moisture increase in the boundary-layer, but the capping inversion is forecast to remain quite strong.

DISCUSSION

Southern Italy and Adriatic, southern Balkans, Bulgaria and surroundings

Within the south-westerly jet, a jet streak ejects from the base of the long-wave trough and spreads across the east Mediterranean into Greece. Several vorticity maxima will travel into the forecast area on Tuesday.

The affected air mass is characterized by a rather cool boundary layer air mass with moisture pooling over some regions. Best moisture will evolve over southern Italy ahead of an approaching cold front as well as along a frontal boundary from Serbia to Bulgaria, where low-level convergence exists. Diurnal heating and increasing lapse rates will likely allow for CAPE during the day.

A few rounds of storms are expected to spread east on Tuesday, with widespread storms over central Italy and from the central Balkans to the Black Sea. With 20 m/s deep layer vertical wind shear, especially the southern regions will see well-organized storms, and supercells and bow echoes are forecast. Main threat will be large hail and severe wind gusts with these storms, although excessive rain and a tornado are not ruled out.

Further south, storm initiation is not that probable given the large inversion atop of the boundary-layer. Diurnal heating may support storms over southern Italy and parts of Greece, and some isolated supercells are forecast, capable of producing large hail. These storms may weaken after sunset.

Eastern Iberia

Along the sea-breeze convergence, easterly onshore-winds will allow for upslope flow and moisture advection over eastern Iberia. Steep lapse rates spreading east from the Iberian mountains will overlap with this moisture and CAPE is forecast. Initiation is most likely over the mountains and storms may move east later on. A capping inversion near the sea will likely limit the storm potential. However, near the sea-breeze convergence, 15 m/s deep layer vertical wind shear can support mesocyclones. Large hail will be possible with these storms as well as severe wind gusts, especially when storms will interact with deep boundary layers from the south-west. Convection is forecast to decay after sunset.

West Mediterranean

Near the base of the trough, rather rich low-level moisture and rather steep lapse rates will create some CAPE. Storms are forecast due to some low-level convergence and weal CIN. Given weak vertical wind shear, degree of organization will be weak over most places. Locally large hail and excessive precipitation are not ruled out with the slow moving storms. When clusters can develop, isolated wind reports are not ruled out as well.

The best potential for better storm organization exists south of the Balearic Islands. Stronger deep layer vertical wind shear is expected to support supercells or bow echoes, capable of producing large hail and severe wind gusts. The overall threat is rather weak, though, given the weak instability, low-level vertical wind shear, and lift.