Storm Forecast
Valid: Thu 18 Jun 2015 06:00 to Fri 19 Jun 2015 06:00 UTC
Issued: Wed 17 Jun 2015 21:34
Forecaster: GATZEN

A level 2 was issued for northern Morocco and northern Algeria mainly for large hail and to a lesser extend tornadoes.

A level 1 was issued for western Turkey, the Aegean Sea, and parts of Greece mainly for large hail.

SYNOPSIS

Between low geopotential across northern Europe and a subtropic high west of the Bay of Biscay a jet stream is directed towards the British Isles and the North Sea. The northern trough will start to expand southward during the period, allowing deep polar air to spread into Germany and Poland. Cool air masses are also already present across eastern Europe that is covered by a broad long-wave trough. An embedded cut-off low will migrate from Italy to southern Greece. Another cut-off is present across the SW Mediterranean.

DISCUSSION

North-east Algeria and north-west Morocco

At the southern flank of the Mediterranean cut-off, a south-westerly jet streak will affect northern Algeria. At lower levels, an intense frontal boundary will be placed across the Atlas mountains, leading to easterly winds along the Mediterranean coasts, and upslope winds across northern Morocco and Algeria. Rich low-level moisture spreading on-shore will overlap with lapse rates from the Atlas region, leading to about 500 J/kg MLCAPE. Thunderstorms are forecast given the strong forcing ahead of the approaching trough, as well as upslope flow. Storms that manage to initiate will quickly organize given 25 m/s deep layer vertical wind shear and supercells are forecast, capable of producing large or very large hail. Although low-level buoyancy is limited, strong low-level vertical wind shear around 10 m/s may also allow for tornadoes. Storms will gradually decay after sunset.

Greece, Aegean, W Turkey

A vort-max/short-wave trough travels around the base of the east-European trough, moving from W Greece to central Turkey during the forecast period. Backing low-level winds ahead of this vort-max will allow rich boundary-layer moisture to overlap with diurnally driven steep lapse rates across Greece and Turkey. Models indicate MLCAPE up to around 1000 J/kg. Thunderstorms are expected due to upslope flow and sea-breeze convergences. Storms are first forecast across Greece below the vort-max, later on convective activity is expected to spread east into Turkey.

The best conditions for organized storms are forecast across northern Turkey into the north Aegean. A moist easterly low-level flow is expected to overlap with south-westerly mid-level winds, leading to about 15 m/s 0-3 km bulk shear. Although low-levels will be relatively cool, some storms are forecast, that may become multicells or supercells, capable of producing large hail. Further south and west, the potential of large hail will remain given stronger deep layer vertical wind shear and increasing lapse rates. Limiting factors will be a rather weak overlap of steep lapse rates with rich low-level moisture. A level 1 was issued.