Storm Forecast
Valid: Thu 15 Jun 2017 06:00 to Fri 16 Jun 2017 06:00 UTC
Issued: Wed 14 Jun 2017 22:59
Forecaster: GATZEN

A level 1 was issued for eastern France, northern ALpin region, and south-western and central Germany mainly for severe wind gusts and to al esser extent large hail.

A level 1 was issued for the western and central Alps mainly for large hail and excessive precipitation.

A lvel 1 was issued for central, northern, and eastern Spain mainly for severe wind gusts and large hail.

A level 1 was issued for the western and southern Balkans, central Italy, and the southern Black Sea region mainly fo large hail and excessive precipitation and to a lesser extent severe wind gusts.

SYNOPSIS

A north-westerly flow is present across Europe, with a deep trough over the east and a subtropic ridge over the south-west. Weak vorticity maxima travel across the Adriatic as well as over northern Turkey. Upstream, a trough travels into westrn Europe during the day, crossing Germany until Friday morning. The associated cold front will be a focus of convective storm development.

DISCUSSION

Germany, eastrn France, northern Alpine region

Warm air advection is expected Thursday ahead of the approaching trough. The plume of warm air mass will be rather stable initially, but lapse rates will increase due to expected strong diurnal heating. A tongue of rich low-level moisture currently over central France will advect north-eastward ahead of the approaching cold front so that CAPE can build over eastern France and south-western Germany in the late afternoon and evening.

Ahead of the cold front, initiation is expected across eastern France and southern Belgium. Rathe short straight-line hodographs will not support storm organization. Instead, storms are expected to cluster and spread eastward into Germany in the late afternoon and evening. Main threat with these clusters are severe wind gusts and locally large hail, especially across south-western Germany. Clusters of storms continue to move east over southern Germany, but rather dry low-level air mass is expected to cause gradually weakening of the storms, but some elevated storms may continue through-out the night.

Further north, weaker CAPE is expected and stronger forcing along the cold front will support a more linear system of rather weak storms, locally producing severe wind gusts, most likely across central Grmany, where overlap of CAPE, shear and frontogenetical forcing is best. Storms are forecast to weaken after midnight when they run in a cool and dry boundary layer. However, continuing DCVA can support redevelopment of (elevated) storms through-out the night.

Western and central Alps

Rich moisture and steep lapse rates resut in moderate CAPE. Storms are expected over the mountains in the noon and afternoon. Deep layer vertical wins shear will increase to 15 m/s from the west in the evening hours, supporting multicells. These can be capable of producing large hail and excessive rain, especially over the western Alps, where CAPE is highest. Due to the approaching trough, some convective activity will likely survive the night hours and expand eastward in the morning hours.

Spain

Relatively moist air will be strongly heated during the day. eak CAPE in expected and storms can initiate in the afternoon hours over the mountains. Deep boundary layer favors dry microbursts. Additionally, large hail can occur, especially over the Pyrenees, where CAPE is highest. Convective activity is expected to decay in the evening hours.

Italy and western Balkans to Greece and northern Turkey
With modrate to rich low-level moisture, locally steep lapse rates an QG forcing due to mid-level short-wave troughs embedded in the north-westerly flow, storms are expected to develop in the afternoon. Although vertical wind shear is rather limited with about 10 to 15 m/s, locally large CAPE in the order of 1000 J/kg can promote a risk of large hail and local flash floods. Downbursts are also not ruled out. In the evening, storms are generally forecast to decay.