Storm Forecast
Valid: Wed 21 May 2025 06:00 to Thu 22 May 2025 06:00 UTC
Issued: Tue 20 May 2025 09:12
Forecaster: TUSCHY

A level 1 was issued for parts of the Adriatic Sea and the Balkan States mainly for a regionally augmented risk of either or all of the following hazards: heavy rain, large hail, severe gusts and an isolated tornado event.

A level 1 was issued for SW Germany mainly for some hail and heavy rain reports.

SYNOPSIS

Once again a high-latitude blocking event (the last impact of the waning stratospheric final warming event of March 9, 2025) evolves with positive geopotential height anomalies stretching from the E Atlantic N towards Iceland. A broad cyclonic gyre over Scandinavia becomes established and supports the influx of a cool and rather stable airmass from the N.

Along the S fringe of that Scandinavian vortex, numerous low-amplitude waves shift SE/E: one over France, another one from Italy to the Balkan States and a third one deep into Russia.

Despite a broad plume of unstable air, covering most of S-CNTRL Europe, this airmass is either avoid of stronger shear or suffers from strong capping issues so the overall risk of organized DMC activity remains manageable.

... S Adriatic Sea and parts of the Balkan States ...

Overall there are numerous areas with enhanced DMC activity forecast.

One will be over the S Adriatic Sea and along the highlighted coastal areas, where strong to severe thunderstorms bring heavy rain and strong gusts next to some hail. In addition, augmented LL CAPE along the coasts indicates a risk of a few waterspouts.
A longer-lived MCS is possible in the vicinity of Lake Scutari and surroundings, as orographically enhanced SE-erly BL flow advects a seasonable moist marine airmass through the Strait of Otranto into ongoing thunderstorms. Temporal back-building is possible next to a waterspout risk.

Another area of concern for scattered initiation arises along parts of the Dinaric Alps. Thunderstorms move E and hence off the orography into a moist and unstable environment with up to 1000 J/kg MUCAPE and 10-15 m/s DLS. The final shear magnitude remains a bit unclear as models continue to indicate slight geometric variabilities of the passing upper wave. EZ and GFS however show an environment supportive of numerous multicells and transient supercells on a more isolated scale. Hail, strong to isolated severe gusts and heavy rain becomes the main hazard. We expanded the level 1 well into Bulgaria to account for a faster storm motion, which advects the thunderstorms more rapidly E. An isolated tornado event cannot be ruled out but no maximized rik area can be detected (mainly driven on the mesoscale or by the orography).

A maximized severe risk could evolve over S North Macedonia into N-Greece but there remain uncertainties. One question is the lingering and slightly elevated morning convection in the WAA regime, which could lower diabatic heating and final CAPE magnitude during the day. If we get some better clearing, a few longer-lived and severe thunderstorms are certainly possible. Another uncertainty remains the final strength of the 0-3 km wind field, which also depends on the finaly geometry of the wave.
Most models however upport decent shear especially in the 0-3 km layer (up to 20 m/s) with strongly curved hodographs. MUCAPE is sufficient with 500 to 1000 J/kg. One or two supercells are possible, which would be accompanied by a combined severe wind gust and isolated large hail risk.

During the night a general weakening trend is expected although a few cells could stay alive until midnight.

... SW Germany into E France ...

A regional upgrade to a marginal level 1 situation was performed over SW Germany. MUCAPE in the 500-1000 J/kg range overlaps with 10 to locally up to 15 m/s DLS. Scattered CI is expected during the day and a few cells may carry a temporal hail, gust and heavy rain threat. The combination of high storm coverage and mentioned background parameters caused this local upgrade.

Further W into E France, LLCAPE increases but the funnel risk may be hampered by a deeper mixed BL.

... Lightning areas ...

Numerous areas with enhanced thunderstorm probabilities are forecast but either CAPE or shear or both parameters remain too marginal for anything severe. Isolated events however are possible but these events are mainly driven on the mesoscale.
We expanded the lightning area into the Baltic States to account for numerous nocturnal/elevated thunderstorms.