Storm Forecast
Valid: Fri 23 Jun 2023 09:00 to Sat 24 Jun 2023 06:00 UTC
Issued: Fri 23 Jun 2023 09:01
Forecaster: GROENEMEIJER

A level 3 was issued across far southeastern Austria, southwest Hungary, eastern Slovenia and northern Croatia for damaging wind gusts, very large hail, and to a lesser extent for very heavy rainfall.

A level 2 was issued across the northwestern and central Balkans and Hungary for very large hail and severe wind gusts and to a lesser extent for very heavy rainfall.

A level 1 was issued across an area surrounding the level 2 areas for the same hazards.

SYNOPSIS

A cut-off low is expected to develop across the northern Adriatic Sea from a trough initially with an axis from northeast Germany to Italy. An extremely unstable air mass is in place across the western Balkans and Hungary with MLCAPE in the 2000-4000 J/kg range. A round of severe storms is expected to develop today as the capping inversion gradually erodes sufficiently to allow for initiation.

DISCUSSION

Austria, Western Balkans, SW Hungary...

Storms are expected to initiate over the southeastern Alps during the afternoon. MLCAPE around or above 2000 J/kg and strong 15 m/s bulk shear in the 0-3 km layer suggest that updrafts may become very powerful and produce very large hail well in excess of 5 cm. With a predicted LCL height of about 2.0-2.5 km ample strong hydrometeor evaporation below cloud base is expected. This should aid the formation of a bow echo moving southeastward into Slovenia, Hungary, Croatia, and later possibly into Serbia and Bosnia. As this happens, the main threat should transition to very strong wind gusts. Ahead of this system, scattered initiation of cells - most prominently off the Dinaric Alps - is expected as well. Profiting from up to 4000 J/kg of MLCAPE, these cells will be able to produce very large hail as well, along with isolated strong downbursts.

Slovakia, Hungary, Western Romania...

Another likely focus for convective initiation will be the southern Tatra mountains. It is expected that isolated storms, that develop into a very unstable air-mass with 3000 J/kg MLCAPE and moderate 10 m/s 0-3 km km bulk shear, will merge along a common outflow boundary and propagate south to southeastward into the eastern Pannonian Plain and western Romania. Initially, the main risk of these storms will be very large hail and isolated downbursts, while this will gradually change to mostly a substantial risk of strong wind. Any cells developing in isolation, however will continue to have a risk of very large hail.

Southwestern Russia and northern Ukraine...

In vicinity of a subtle frontal wave, a number of convective storms are expected to occur in an environment with modest (500-1000 J/kg) MLCAPE, but substantial low-level shear and rather curved low-level hodographs. This suggests some risk of tornadoes and severe wind gusts will exist. In addition a modest risk of large hail will exist with any well-organized supercell that manages to form.