Storm Forecast
Valid: Thu 07 Jun 2018 06:00 to Fri 08 Jun 2018 06:00 UTC
Issued: Thu 07 Jun 2018 06:47
Forecaster: GATZEN

A level 1 was issued across central Italy for large hail and severe wind gusts.

A level 1 was issued across Belgium, south-west Germany, central and southern Austria mainly for locally extreme rainfall and large hail.

A level 1 was issued across northern Turkey mainly for large hail.

SYNOPSIS

Subtropical ridge extends from the Mediterranean across the Balkans and Central Europe towards the British Isles. Small-scale mid-level vortices are present over western and south-western Europe, with a cut-off low moving across the west Mediterranean north-eastwards. It provides DCVA and synoptic-scale lift downstream across the northern central Mediterranean during the period. At lower levels, a plume of well-mixed desert air ejects into the south Mediterranean and is associated with warm air advection across the central and east Mediterranean. Downstream, a weak trough affects Turkey. Dry air masses affect northern and most of eastern Europe.

DISCUSSION

Central Italy

Ahead of the approaching trough axis, steep lapse rates are advected northward towards central Italy. Low-level moisture is limited according to latest soundings, however, model guidance indicates moisture increase in particular along the sea-breeze convergence across central Italy during the day. CAPE is expected to reach about 1500 J/kg close to the Adriatic Sea. Given relatively small CIN, initiation is expected across central and northern Italy. Moderate vertical wind shear increasing to about 15 m/s in the lowest 6 km supports multicells capable of producing large hail and severe wind gusts. Increased vertical wind shear can be supposed close to sea breeze convergence lines, and supercells are not ruled out with a threat of producing very large hail, damaging wind gusts and locally excessive precipitation.

Farther south, large CIN will limit chances of initiation. Farther north, vertical wind shear is weaker. Single cells and brief multicells are expected across northern Italy that could produce locally excessive precipitation.

In the evening and night hours, further storms are expected to move north-east. Despite stronger deep lpyer vertical wind shear, low-level cooling will limit severe weather threat of these storms. Isolated large hail is possible with the stronger storms.

Northern Turkey

Upslope low-level flow transports Black Sea moisture into Turkey then partly overlaps with steep lapse rates in the afternoon. Vertical wind shear is around 10 to 15 m/s, and multicells could produce locally large hail. Storms will decay after sunset.

Southern Benelux into southern Germany and Austria

A convergence zone associated with high precipitable water content remains quasistationary from southern Netherlands and Belgium towards southern Germany. Due to rich low-level moisture, CAPE evolves in response to diurnally steepening lapse rates and due to weak CIN, thunderstorms will develop over the mountains. Storm motion will be north-westward along the convergence zone increasing the potential of torrential rainfall. Additionally, large hail is forecast with the stronger storms before storms merge and cluster along the convergence line. Farther east, isolated storms may produce severe wind gusts due to the deeper and drier boundary layer.

Central Balkans to Bulgaria

Diurnally driven storms in a weakly-sheared environment with moderate CAPE can be associated with locally excessive precipitation and large hail.