Severe thunderstorm outbreak with large hail and tornado risks across Europe

A powerful low-pressure system with mean sea level pressure values of 970–975 hPa, centered over northwestern Europe and extending toward Iceland, is generating a cyclonic west to southwesterly flow across the continent on June 3.

This system, combined with a strengthening blocking ridge over southeastern Europe, is creating conditions conducive to widespread severe thunderstorms. A zonally aligned synoptic-scale front stretching from northern Spain to Ukraine serves as the primary focus for deep moist convection.

Eastern and northeastern Spain, and far southwestern France are under a Level 2 warning for large to very large hail over 5 cm (2 in), severe wind gusts, and heavy rainfall. MUCAPE values of 1 000–1 500 J/kg and deep-layer shear of 20–25 m/s (66–82 ft/s) support the development of long-lived multicells and supercells. Storms are expected to weaken after sunset on June 3 due to destructive interference between cells.

South-central and eastern France, extending into Switzerland, northern Italy, southern Germany, and Austria, are under multiple Level 2 warnings. MUCAPE values of 800–1 500 J/kg and deep-layer shear of 15 m/s (50 ft/s), combined with orographic lifting, will trigger scattered convective initiation by the afternoon.

These areas may experience classic to high-precipitation supercells, with risks of large hail, severe wind gusts, heavy rainfall, and isolated tornadoes.

Northeastern Switzerland, southern Germany, and northern Austria are also under a Level 2 warning, with 0–3 km (0–1.8) shear reaching 20 m/s (66 ft/s), enhancing storm-relative inflow.

The ICON model indicates conditions favorable for multicells, bowing segments, and supercells capable of producing hail larger than 5 cm (2 in), severe winds, and heavy rainfall. An isolated tornado risk exists due to favorable low-level shear.

Southeastern Austria into western Hungary is under a borderline Level 2 risk, with potential for organized multicells and isolated supercells. MUCAPE values of 1 000–1 500 J/kg and deep-layer shear of 15 m/s (50 ft/s) support large hail, severe gusts, and heavy rain, although increasing convective inhibition may limit storm longevity. An isolated tornado is possible during the discrete storm phase.

Northeastern Italy is under a Level 2 warning, with MUCAPE values near 1 500 J/kg and deep-layer shear of 15 m/s (50 ft/s) supporting well-organized multicells and isolated supercells. Despite weak background lift, storms are expected to produce large hail, severe gusts, and heavy rainfall. Convective initiation may be limited but remains a concern.

Eastern Slovakia, western and northern Ukraine, and southern Belarus are under Level 2 warnings, with MUCAPE values of 1 000–1 500 J/kg and deep-layer shear of 15 m/s (50 ft/s). A southeastward-moving cold front will initiate multicells, bowing segments, and supercells capable of producing large to very large hail, severe downbursts, and heavy rainfall. Upscale growth into a mesoscale convective system is possible overnight.

Poland and the Baltic States face a Level 1 risk, with MUCAPE values of 300–600 J/kg and strong deep-layer shear supporting organized thunderstorms. Isolated convective initiation is expected after 12:00 local time (LT), with risks of hail, gusty winds, heavy rainfall, and an isolated tornado, particularly in northeastern Poland, northwestern Belarus, and southeastern Lithuania.

In northern Algeria, thunderstorms along the Atlas Mountains are expected to produce large hail and severe downbursts. Mid-level CAPE and adequate shear will support rotating updrafts, posing localized severe weather risks. These storms are under a Level 1 warning.

The ESTOFEX forecasting system uses a three-level risk scale, with Level 2 indicating an enhanced risk of organized severe weather. Historical evaluations show reliable performance, with Area Under Curve metrics showing strong forecast accuracy, particularly during the warm season.

Residents in affected regions are advised to monitor local weather updates closely from June 3 through early June 4, as conditions may change rapidly. Severe thunderstorms pose risks of large hail, damaging winds, flash flooding, and isolated tornadoes, requiring attention to local meteorological guidance. Recommended protective actions include seeking substantial shelter and avoiding outdoor activities during storm activity.

References:

¹ Storm Forecast – ESTOFEX – June 2, 2025