Storm Forecast
Valid: Thu 28 May 2020 06:00 to Fri 29 May 2020 06:00 UTC
Issued: Thu 28 May 2020 07:37
Forecaster: GATZEN

A level 1 was issued across north-east Ukraine and south-west Russia for large hail, tornadoes, and severe wind gusts.

A level 1 was issued across east Urkaine, south-west Russia, Georgia, Armenia, Azerbaijan and east Turkey for large hail, severe wind gusts, and excessive rain.

A level 1 was issued across north Italy, Slovenia, south-west France mainly for marginal large hail.

A level 1 was issued across north Morocco and north Algeria mainly for large hail and severe wind gusts.

SYNOPSIS

Broad low geopotential across eastern Europe yields a strong southerly mid-level flow from the east Mediterranean to southern Russia. Embedded vorticity lobes move across Turkey and Ukraine. In the wake of the east-European trough, a short-wave trough moves south across Central Europe, and another mid-level trough affects north-western Africa. Most of north-western Europe is influenced by mid-level ridging, whereas north-eastern Europe is crossed by a short-wave trough embedded in the polar jet.

At lower levels, main feature is a deepening surface low across southern Urkaine that will move northward, and its cold front that crosses the Black Sea region to the east.

DISCUSSION

Central and east Ukraine

A moist air mass is present across the region, with a cool and stable boundary-layer as indicated by latest observations. A warm front moves into eastern Urkaine today and gradually spreading westward north of the deepening surface low. The air mass within the warm sector is unstable with MLCAPE around 1000 J/kg. However, synoptic-scale subsidence at the anticyclonically sheared flank of the jet will not support lift east of the approaching cold front, and most models suggest initiation rather late in the period, when low-level already start to become stable. Most likely scenario is that storms form in the evening and night and gradually become elevated in response to boundary layer cooling. Nevertheless, moderate deep layer shear will support storm organization, so that multicells and supercells are not ruled out, capable of producing large hail and flash floods. Storms that form in the afternoon will pose an additional threat of severe wind gusts.

Across central Urkaine, potntial for initiation is weaker. Elevated storms are expected north of the warm front and surface low-pressure center. However, if low-level clouds will break up and diurnal heating takes place, rapid destabilization can be expected, and storms can develop. If this scenario comes true, very strong vertical wind shear and favorably curved low-level hodographs will suppport supercells, capable of producing tornadoes. Strong tornadoes are possible due to the strong low-level shear. Confidence is too low to issue a higher threat level, but the situation must be monitored closely during the afternoon adn evening.

South-west Russia, Georgia, Armenia, Azerbaijan and east Turkey

Thunderstorms across the mountains are expected today due to a moist boundary layer and diurnal heating. With moderate deep-layer shear around 15 m/s, multicells are expected to be the dominant storm mode. Mid-level lapse rates increase from west to east and the potential of large hail is forecast to increase to the east as well. Furthermore, severe wind gusts and local flash floods are not ruled out. Storms are foreacst to decay in the afternoon and evening.

Southern Alps

Some low-level moisture is expected to overlap with steep lapse rates spreading south from the Alps in the afternoon. The approaching mid-lvel trough will support some steepening of the lapse rates as well. Along the upslope low-level flow, thunderstorms are forecast in the afternoon and evening. CAPE and deep-layer shear are not too impressive, however, some locations may experience around 20 m/s deep-layer shear supportive for supercells. Main threat is large hail with these storms. Late in the period, mre storms can move across northern Italy that will gradually become elevated with a weakening severe weather threat.

North-western Africa

Over the Atlas mountains, another round of storms is forecast within a westerly flow ahead of the south-west European trough. Moderate deep-layer shear and CAPE will support multicells with some large hail possible, especially in the western parts where mid-level lapse rates and CAPe are larger. To the south and east, dry bohndary-layers can support dry microbursts.