Storm Forecast
Valid: Sat 24 May 2025 06:00 to Sun 25 May 2025 06:00 UTC
Issued: Fri 23 May 2025 21:01
Forecaster: TUSCHY

A level 2 was issued for parts of Bulgaria to E Romania into Moldova for (very) large hail and severe gusts.

A level 1 surrounds that level 2 for similar hazards but with lowered probabilities.

A level 1 expands N to NW Russia for a mix of large hail, gusts and heavy rain but also for a tornado risk.

A level 1 was issued deeper into Russia for hail and heavy rain.

SYNOPSIS

Europe gets affected by a residual blocking pattern over the E, whereas a more progressive zonal flow pattern starts to evolve over the NE Atlantic towards W Europe.

A deep longwave trough extends from Scandinavia down towards Libya and fractures into numerous lower amplitude waves/troughs. No significant east motion occurs as blocking ridge persists over far E Europe into W Russia. A wavy frontal boundary frames this trough along its E fringe and features numerous more or less pronounced LL vortices, which disturb the LL flow and the front itself. East of that front a plume of modest MUCAPE expands far N into NW Russia with another round of active DMC activity forecast along the front's periphery.

Over NW Europe, a lead low-amplitude wave affects Ireland/Scotland during the forecast period in a more zonally aligned background flow/high index pattern. The passage of a cold and occluded front with an eastward spreading dry slot create a regional setup for somewhat enhanced thunderstorm probabilities.

DISCUSSION

... N-Macedonia to Bulgaria to E Romania into Moldova ...

A moist and unstable airmass resides E of the quasi-stationary front, which awaits a structuring LL depression from the S. This vortex lifts N during the day which could even push the front to the N/NW a bit. Overall the main focus for organized convection over Bulgaria arises between the Balkan and the Rhodope Mountains, where 1000-2000 J/kg MUCAPE overlap with 25 m/s DLS and up to 20 m/s 0-3 km shear. Forecast hodographs respond to the approaching vortex with strongly looped signatures, indicating a deep WAA regime. Any deviating cell will keep its updraft avoid of the precipiation and numerous long-tracked and severe supercells are forecast to race E/NE towards the Black Sea. Weak LL shear, strong and deep SR inflow into growing cells and broadening mid-level CAPE in strong shear point to a (very) large hail threat and hail diameter in excess of 5 cm can occur. Severe gusts will be another issue. These storms move offshore beyond sunset and start a weakening trend.

We expanded a level 1 far W into N Macedonia and far N Greece to account for a severe risk more on the isolated scale. MUCAPE in the 400-1000 J/kg range overlaps with impressive kinematics. However NWP guidance indicates some issues with isentropic upglide along the front, which could add a broad area of more stratiform rain. The main focus for more discrete cells evolves along the S fringe of the rainy mess. Impressive SRH supports rotating updrafts with hail (isolated large) and severe gusts the main hazard.

Further N over E Romania into Moldva, the overall severe risk is not as intense with DLS more in the 15 m/s range. However, CAPE up to 2000 J/kg on a regional scale combined with mentioned shear is still enough for severe multicells and a few supercells. The hodographs turn a bit more straight, so splitting cells are more likely, which increases destructive interference betimes. Despite more relaxed shear, we expanded the level 2 into this area to account for numerous severe hailstorms, which could produce very large hail with hail diameter in excess of 5 cm in the most organized storms. Severe gusts and heavy rain will be another issue.

... Belarus N into far NW Russia ...

Early and widespread CI is forecast along the boundary. Initiating cells grow in a 500-1000 J/kg MUCAPE and 15 m/s DLS setup, which is enough for multicells and isolated supercells. However, this activity won't stay discrete for that long and rapid upscale growth into an extensive N-S aligned cluster is forecast. Initiating cells pose a hail and gust threat, which turns more to heavy rain betimes. However, cells near the front see impressive LL SR inflow into cells, where LCLs lower to 700-800 m AGL. A few tornadoes are certainly possible in this kind of environment. We thought about a regional upgrade, but the rapid clustering mode could limit time for producing severe. However, more clustered reports are certainly possible.

Another level 1 was added to the E for slow moving storms with isolated hail, gusts and heavy rain.

... Ireland ...

Ongoing NWP issues keep confidence in organized convection on the lower side. Dependant on how fast the dry slot advances E, we could see a more extensive plume of enhanced MUCAPE, what EZ indicates. Other models like GFS or ICON stay way more reluctant regarding CAPE although all models show subtantial shear at all levels. This will certainly be a nowcast event, where trends for clearing behind the departing fronts and along the periphery of the dry slot need to be monitored next to the BL moisture. In case EZ verifies a few organized updrafts with some hail and gusts are possible including an isolated tornado threat with very low LCLs. Parts of the high probability lightning area could see an upgrade per mesoscale discussion if the more aggressive solution becomes more probable.