Storm Forecast
Valid: Sun 08 Jun 2025 09:00 to Mon 09 Jun 2025 06:00 UTC
Issued: Sun 08 Jun 2025 09:08
Forecaster: PISTOTNIK

A level 3 is issued for the far-NW Ukraine mainly for large hail and severe convective wind gusts, and to a lesser degree for tornadoes.

A level 2 and level 1 are issued for far-SE Poland, parts of Belarus and Russia for large hail, severe convective wind gusts, excessive convective precipitation and to a lesser degree for tornadoes.

A level 2 and level 1 are issued for E Slovakia, E Hungary, parts of Romania and the Ukraine mainly for large hail and severe convective wind gusts.

A level 1 is issued for NE Slovenia and NE Croatia mainly for large hail and excessive convective precipitation, and for adjacent SW Hungary mainly for severe convective wind gusts.

A level 2 and level 1 are issued for parts of Germany, Poland, the Czech Republic and Austria for severe convective wind gusts and to a lesser degree for tornadoes.

SYNOPSIS

An unseasonably intense mid-level low remains moored in the Norwegian Sea. Its circulation influences large parts of Europe. The axis of a 25-35 m/s mid-level jet runs from the British Isles to central Europe, Belarus and NW Russia. It is largely collocated with a broad and diffuse, more or less stationary frontal zone. In response to vorticity maxima aloft, several small wave- or comma-like disturbances run eastward on the cyclonic side of the frontal zone from Germany to NW Russia.
South of the frontal zone, very warm to hot and anticyclonic conditions dominate across Iberia, the Mediterranean Region and the Balkans.

DISCUSSION

... east-central Europe into Belarus, Ukraine and W Russia ...

Plentiful insolation on the warm side of the frontal zone allows the buildup of CAPE on the order of 1000 to 2500 J/kg again, as rich low-level moisture is concentrated beneath decent mid-level lapse rates. Moisture is maximized along the frontal zone itself as well as along outflow boundaries laid out from overnight's convection. At the time of writing (Sun 08 UTC), high-resolution satellite imagery does not reveal any such boundary, though, and the poor station density does not allow any further conclusions.
Deep-layer shear increases from 10 to 20 m/s from SE to NW across the unstable airmass. Two intense short-wave troughs overspread it and provide large-scale lift that erodes the capping inversion and facilitates convective initiation. Both are also accompanied by wave developments along the frontal zone that further tighten the low-level wind field and the frontal boundary, hence another round of severe to extreme storms is likely especially along these two frontal waves and in their warm sectors, where strong low-level shear (more than 10 m/s) and storm-relative helicity (more than 200 m2/s2 across the 0-1 km layer and more than 400 m2/s2 across the 0-3 km layer) become available.
The eastern short-wave trough overspreads roughly the eastern third of our level 2 area and adjacent regions north of it during peak heating hours. The second one moves from Poland into Belarus and the NW half of the Ukraine. Scattered convective initiation from the early afternoon onwards and a quick organization into supercells with a primary hazard of large to very large hail are expected ahead of both features. Later on, upscale growth into large clusters appears likely, and one or two bow echoes are not ruled out, which would be capable of widespread severe and isolated to scattered extreme wind gusts. This scenario is somewhat mitigated by the unfavorable angle of the short-wave trough with respect to the frontal zone and by rather moderate lapse rates, though. Nonetheless, also supercells can produce severe or even extreme downbursts, albeit on a more local scale.
With several long-tracked supercells and such a strong low-level wind field, a few tornadoes are possible, and even a strong and long-lived tornado is not ruled out. The (relatively) most likely time frame is the evening, when the boundary layer starts to stabilize and the near-surface wind field becomes more laminar. By then, the warm sector of the second frontal wave will overspread SE Belarus and immediately adjacent areas of the Ukraine.
Convection will again continue well into the evening and night with slowly decreasing severe weather hazards, while excessive rain may become an additional issue especially with training storms or large clusters. Further east into Russia, convection will outrun the zone of noteworthy CAPE and start to weaken betimes.

Similar to Saturday, the the confidence of this forecast is somewhat limited for Russia due to the lack of high-resolution models, surface observations and radiosondes. Therefore a broad level 2 is issued as a compromise between possible swaths of more widespread extreme hail or wind events, worthy of a level 3, and other areas that could stay largely or completely devoid of severe weather. With respect to the second frontal wave, the availability of convection-resolving forecast models and the presence of mountains (Tatras and Carpathians) increase the forecast confidence and narrow down the possible initiation sizes enough to upgrade a limited zone to a level 3.

Scattered multi- and supercells are also expected in E Slovakia, E Hungary and N Romania in the afternoon and evening, but coverage of storms will be lower due to less CAPE and a lack of large-scale lift. This area is covered by a level 1.

... southern Alpine region into Hungary ...

The tail of the cold front slowly crosses the main Alpine crest. Some hundred J/kg CAPE under strong deep-layer shear in excess of 20 m/s are in place ahead of the front, but cold air advection will create pronounced large-scale subsidence and reduce the chances for convective initiation. Some storms will likely form over S Austria, NE Italy and Slovenia, but mostly embedded into the rain shield and/or quickly undercut by the rush of low-level cold air around the eastern Alps. Heavy rain can occur, but should stay below our severe threshold.
Tail-end and surface-based storms towards the south can turn into supercells, but are highly questionable. Only a small area in NE Slovenia and NE Croatia is upgraded to a level 1 for large hail and excessive rain, since the latest ICON-D2 runs (plus ensembles) agree increadingly on a single supercell in the brief time window available before the low-level cold air arrives. The level 1 is also extended into SW Hungary, since the rush of low-level cold air can also produce strong to isolated severe wind gusts (along with high quantities of raised dust) even ahead of convection, or after its decay.

... Germany, N Austria, Czech Republic, Poland, Baltic States ...

The maritime polar airmass on the cool side of the frontal boundary features a neutral to slightly unstable stratification. Deep-layer shear is weak in N Germany and NW Poland, but quickly increases to 25-35 (!) m/s beneath the jet axis towards the south. A third short-wave trough crosses the area and sparks another comma-like feature. Latest model runs have increased the overlap of its pronounced lift with the unseasonably strong wind field toards the south.
After some hours of daytime heating, a few hundred J/kg CAPE can develop, and scattered thundery showers will occur from noon to sunset. Despite low cloud tops, the effective shear appears strong enough to allow an organization into multicells, supercells and short bowing lines. Scattered severe wind gusts are expected, and even longer swaths are possible from far-E and -SE Germany into Bohemia. With rather low cloud bases and 10-15 m/s low-level shear in place, one or two tornadoes could occur as well, especially with supercells deviating from the background wind field.