Storm Forecast
Valid: Sun 30 May 2021 06:00 to Mon 31 May 2021 06:00 UTC
Issued: Sat 29 May 2021 15:16
Forecaster: PISTOTNIK

A level 1 is issued for W Russia mainly for excessive convective precipitation.

A level 1 is issued for the Russian Caucasus region, Georgia and Armenia mainly for excessive convective precipitation and to a lesser degree for large hail and severe convective wind gusts.

A level 1 is issued for SW Turkey mainly for large hail and to a lesser degree for excessive convective precipitation.

A level 1 is issued for NE Spain mainly for large hail and to a lesser degree for excessive convective precipitation.

SYNOPSIS

A blocking anticyclone stretches from the British Isles to Scandinavia. Further downstream, an aged mid-level trough reaches from NW Russia to E-central Europe and the Balkans. This configuration results in the advection of cool and rather dry continental air from the NE into much of Europe.
The Mediterranean region, Turkey and the Black Sea region are overspread by a moderate zonal mid-level flow. Despite the enhanced temperature gradient to fairly hot air towards the SW (Iberia) and SE (Turkey and Near East), no active frontal systems are discernible.

DISCUSSION

... W and SW Russia, Georgia and around ...

Convection of the past few days has overworked the warm and moist airmass, which results in rather poor lapse rates but plentiful low-level moisture. Some hundred, locally up to 1000 J/kg CAPE will form again on Sunday in response to daytime heating. Scattered to widespread storms are expected especially in the afternoon and evening. Heavy rain is the main risk due to weak vertical wind shear and slow storm motion, especially in the belt ahead of a slowly southward moving cold front that will likely see the highest storm coverage.
Towards the SE (Caucasus region, Georgia and Armenia), deep-layer shear increases to 15-20 m/s, hence some storms can organize better and pose additional risks of large hail and a few severe wind gusts. Limiting factors are the tendency of storms to cluster quickly and become partly embedded in stratiform cloudiness in the weakly to non-capped airmass.

... thunderstorm areas around the Mediterranean Sea ...

Steep lapse rates form especially over orography thanks to strong daytme heating, whereas decent low-level moisture is mostly confined to coastal and offshore areas. In the absence of noteworthy synoptic features, mesoscale circulations like diurnally driven onshore and upslope winds are needed to create at least a confined overlap of these ingredients, which allows a few hundred J/kg CAPE and scattered afternoon storms.
Vertical wind shear is mostly weak in the lower troposphere before it increases to 10-15 m/s across the 0-6 km layer, providing a typical environment for multicells with a risk of isolated large hail and excessive rain. However, apart from parts of Spain and Turkey, forecast soundings suggest rather low convective cloud tops, which reduces the severe weather risk.
Stronger deep-layer shear (up to 20 m/s) and more CAPE (up to 1000 J/kg) are foreseen to overlap in NE Spain, where even a few supercells with a further enhanced hail risk are possible. Limiting factor against a level 2 is a wave of weak, elevated convection that is expected to cross this area from W to E in the morning. Diurnal heating may therefore be delayed and limited, which could keep the storm coverage to some degree lower.