Storm Forecast
Valid: Thu 12 Aug 2021 06:00 to Fri 13 Aug 2021 06:00 UTC
Issued: Thu 12 Aug 2021 00:21
Forecaster: GATZEN

A level 2 was issued across southern and central France for large hail and severe wind gusts.

A level 1 was issued for east Spain towards the Alpine area for large hail and severe wind gusts.

A level 2 was issued across central Black Sea region for heavy rain.

A level 1 was issued for western Russia for large hail and severe wind gusts as well as heavy rain.

A level 1 was issued for the Baltic States for heavy rain.

SYNOPSIS

Southern Europe is influenced by a stationary ridge centred across the west Mediterranean and a stationary trough downstream. To the north, troughs slowly progress across NW Europe and Scandinavia and Baltic States. At lower levels, a broad frontal zone is present from SW Europe to the Alps and northern Balkans, with well-mixed air to the south. A moist and warm air mass is located across the Black Sea. Cooler maritime air spreads into northern Europe in the wake of the Scandinavian trough.

DISCUSSION

France into Alps, east Spain

At the edge of a plume of well-mixed, unseasonably warm air, warm air advection is expected to develop ahead of a weak mid-level trough that curves around the edge of the Mediterranean ridge. Some frontogenesis can be expected with increasing lift in the afternoon, spreading from west to east. Affected air mass is very unstable, with steep lapse rates and rich boundary layer moisture, and MLCAPE will be in the order of 1 to 3 KJ.

Storms are forecast to develop over the mountains of eastern Spain and southern France as well as over the Alps in the afternoon, with higher storm coverage later on over France, spreading north and east.

Vertical wind shear is moderate, with rather strong 0-3 km shear, supporting some multicells and transient supercells that can merge to bow echoes over S France in the evening. Initial threat will be some large or very large hail and severe wind gusts, but some widespread wind events can be expected when storms merge later on and deeper cold pools evolve. Bow echoes are expected to travel east towards the western Alps. Remaining storms are expected across SW Germany in the morning, where severe threat in limited due to elevated nature of convection.

Black Sea

Development of a subtropical storm has started and will continue through-out the period. Ongoind threat of heavy rain producing storms is forecast and flooding is likely within the level 2 area. Within the level 1 area, still some local flash floods are expected due to slow moving storms in a moist profile.

Southern to western Russia

A frontal zone is located ahead of the east European trough, with a well-mixed air mass spreading around the trough across southern Russia where it overlaps with rich low-level moisture advected northward. Together with warm air advection, a mid-level trough approaches from the west, and frontogenesis is expected during the period. Along and east of this front, storms become likely in the afternoon that spread northward.

Moderate vertical wind shear will allow for some well-organized convection including supercells, capable of large hail and severe winds. Some heavy rain is also possible in the southern parts with moist profiles and slower storm motion.

Later on, vertical wind shear increases and a low-level jet forms over western Russia on top of the front. Although some low-level stabilization occurs during the night, ongoing lift will result in MCSs moving north along the boundary, capable of severe wind gusts until the morning.

Baltic States

Slow moving storms promote some heavy rain threat. Weak shear will limit any storm organization.