Storm Forecast
Valid: Thu 27 Jul 2023 06:00 to Fri 28 Jul 2023 06:00 UTC
Issued: Wed 26 Jul 2023 22:11
Forecaster: GATZEN

A level 2 was issued across western Russia mainly for severe wind gusts and to a lesser extent tornadoes, large hail, and heavy rain.

A level 2 was issued across the Black Sea into eastern Ukraine mainly for severe wind gusts, large hail, excessive rain and to a lesser extent tornadoes.

A level 2 was issued for north-eastern Spain for large or very large hail, severe wind gusts and to a lesser extent excessive rain and tornadoes.

A level 1 was issued across the Caucasus region for large hail and severe wind gusts.

SYNOPSIS

The European trough quickly progresses east and starts to form a cut-off across Ukraine as the corresponding Rossby wave breaks. The whole process leads to a strongly-forced synoptic-scale situation, with strong DCVA ahead to the trough and also strong WAA spreading north. The affected baroclinic zone is characterized by steep mid-level lapse rates and increasing low-level moisture with a high potential of convective storms to develop, especially in association with cyclogenesis over the Black Sea and a well-developed warm front across western Russia. Upstream, an intense vort-maximum travels rapidly across Iberia during the period, associated with intensifying WAA over north-eastern Spain, where steep lapse rates can overlap with Mediterranean moisture. Subtle conditions are expected across Scandinavia within the base of the north-European trough with marginal CAPE and shear. At its southern flank, remaining moisture of ex-hurricane DON spreads towards the Benelux countries and northern Germany.

DISCUSSION

Western Russia

Along the warm front of the intensifying east-European low, rich boundary-layer moisture is expected to overlap with steep lapse rates advected north. A powerful 25 m/s 700 hPa jet overlaps with the region of CAPE that will support rapid storm organization. Latest models indicate that a moist air mass with limited lapse rates will be available along the north-western frontal zone in the wake of overnights convective systems. If storms will manage to form in this environment, low cloud bases and very strong low-level shear characterized by large low-level streamwise vorticity indicate a tornado potential with any supercell that develops. Main limiting factors are the uncertainty of low-level buoyancy due to a lack of heating and the possibility of widespread storm clusters with a focus of severe wind gusts. Excessive rain is not ruled out even with fast moving storms due to deep warm clouds.

Along and south-east of the warm front, models indicate better mixed low-levels and weaker 0-1 km shear. However, more robust CAPE and strong frontal lift are expected to increase the potential for intense thunderstorms in this region. Especially in the western part of this area, strong 0-3 km shear pointing towards the north can result in further convective systems rapidly travelling north., with severe wind gusts the main threat. Isolated storms are forecast to become supercells quickly with a potential of large or very large hail. In the afternoon and evening, the intensifying low-level jet and strengthening 0-1 km shear, again characterized with large low-level streamwise vorticity, are associated with a potential for tornadoes, and strong tornadoes are not ruled out. Overnight, upscale growth of the convection will affect large areas in western Russia, with severe wind gusts and heavy rain the main threats.
More storms are expected withing the warm air advection regime, where less vertical wind shear is associated with a somewhat smaller large hail potential, although storms will stay more isolated. Additionally, deep boundary-layer mixing supports a severe downburst threat.

Western Black Sea towards eastern Ukraine

Within the developing cyclone across the Black Sea, strong frontal lift will allow for numerous mesoscale convective systems due to an overlap of steep mid-level lapse rates and rich low-level moisture. In strong 0-3 km shear, these systems will travel towards eastern Ukraine with a potential of strong wind gusts and heavy rain. Additionally, embedded supercells are capable of large to very large hail. An additional tornado threat is forecast north of the low-pressure center along the frontal boundary, where low-level veering profiles are expected.

North-eastern Spain

Ahead of the approaching vort-max, QG forcing is expected, with cyclogenesis across Spain during the day. To its north, easterly low-level flow will advect a moist boundary layer inland, whereas strong mid-level south-westerly flow advects steep lapse rates towards north-eastern Spain. Latest models indicate rather moist profiles, and convection initiation is forecast, with supercells forming that travel east before merging into one or two mesoscale convective systems. Large or very large hail is forecast initially with the severe potential transitioning to strong wind gusts later. Heavy precipitation is forecast as well. Tornadoes are not ruled out due to 10 m/s 0-1 km shear. However, due to a lack of low-level streamwise vorticity, the potential is expected to be limited.

Caucasus area

Ahead of the developing cut-off trough, some storms are expected in an environment characterized by steep mid-level lapse rates and high-based CAPE. These can produce some large hail and severe wind gusts, especially in the afternoon when vertical wind shear increases.