Storm Forecast
Valid: Thu 31 May 2018 06:00 to Fri 01 Jun 2018 06:00 UTC
Issued: Wed 30 May 2018 22:10
Forecaster: GATZEN

A level 2 was issued across north-eastern France into southern Germany and parts of Switzerland and Austria for excessive precipitation and to a lesser extent large or very large hail and severe wind gusts.

A level 1 was issued across the southern British Isles, Benelux, most of Germany, Czech Republic, northern and western Balkans, and Italy mainly for excessive precipitation.

SYNOPSIS

An ill-defined mid-level omega controls the mid-level flow. Troughs are centred west of the Bay of Biscay and over Turkey. Downstream of the omega ridge across southern Scandinavia, an intense trough amplifies into south-western Russia. Whereas arctic air masses advect into Russia in the wake of this trough, warm air remains over large portions of Europe. This warm air is associated with rich low-level moisture and steep mid-level lapse rates, resulting in CAPE of 1000-2000 J/kg in the afternoon. Widespread storms are forecast within the warm air. Large-scale lift will support initiation from the southern British Isles towards northern Italy due to an elongated vort-maximum slowly moving north-east. At low-levels, a convergence zone evolves below the mid-level vort-max that separates the warm air from cooler maritime air masses across western Europe.

DISCUSSION

North-eastern France into southern Germany and parts of Switzerland and Austria, northern Italy

Remnants of overnights storms will continue in parts of the forecast area in the morning and insolation is limited in some places. Areas with strong diurnal heating will experience CAPE of more than 1000 J/kg in the course of the day, together with high precipitable water. Vertical wind shear will be about 15 m/s in the lowest 6 km, supporting multicells and also a few supercells. Main threat is excessive precipitation and local flash flooding. Additionally, large or very large hail and severe wind gusts are possible with the stronger storms. With continuing large-scale lift, storms are expected to cluster and form mesoscale convective systems, travelling north or north-east from the late afternoon well into the night. Excessive precipitation and severe wind gusts will be the main threat after sunset.

Southern British Isles, Benelux, most of Germany, Czech Republic, northern and western Balkans, Italy

In a weakly-sheared but unstable environment, widespread storms are forecast during the day. Main threat is excessive precipitation and local flash floods, but stronger pulse storms can also produce large hail and severe wind gusts. Storms will gradually weaken after sunset.