Severe weather outlook – forecast across Europe. This forecast features areas of organized severe weather with risk levels and severe weather threats across the European continent.
SEVERE WEATHER OUTLOOK
Valid: 28/08/2025 06 UTC – 29/08/2025 06 UTC
Issued by: Severe Weather Europe
Forecaster: Marko Korošec
SUMMARY
A deep upper-level trough formed from the ex-hurricane Erin has established over western Europe and is gradually emerging into continental Europe. This results in a widespread multi-day severe weather outbreak for central Europe and the northern Mediterranean, where volatile environmental conditions combine. Severe thunderstorms will support severe, damaging winds, large to very large hail, a few tornadoes, and especially an intense, excessive rainfall with a flooding threat.
From early Thursday morning through Saturday, multiple rounds of severe thunderstorms are forecast from northeast Spain across southern France to Switzerland, north-central Italy, the Alpine region, the Adriatic region, and the northern and western Balkan peninsula.
See the general weather discussion: A deep trough over Europe prompts a severe weather outbreak for the end of meteorological summer 2025.
This outlook focuses on Thursday, when a significant severe weather event is expected for the southern Alpine flank. The upper wave will emerge over the Alps into the northern Mediterranean. Robust thunderstorms are expected across northern Italy into southern Switzerland, with training cells leading to intense and excessive rainfall that will support flash floods.
Above: Video animation of the convective storm’s development across Europe from Thursday morning through Friday night, August 28th to 29th, 2025.
For this reason, HIGH + MDT risks have been placed across the northern Mediterranean and the Alpine region, with highlighted areas where the most robust severe weather threat will develop on Thursday. The threat also includes enhanced potential for severe damaging winds, tornadoes, and very large hail (5 cm or larger).
SYNOPTIC OVERVIEW
A large upper-level trough over Western Europe is gradually expanding east and south and is forecast to be considerably deep from Thursday to Friday. This will establish a typical volatile setup for the north Mediterranean and the Alpine region.
At the surface, an extensive low-pressure system is centered over Ireland and the UK, with a secondary low forming in the Mediterranean in response to the upper wave moving into the region aloft.
This results in a frontal system entering central Europe, with the cold front moving west to east into the Alps and northern Mediterranean.
WEATHER FORECAST DISCUSSION – Thursday, August 28th
+++ Weather forecast for France, Italy, Switzerland, Austria, and Slovenia +++
Explanations for abbreviations (TSTM, SLGT, ENH, etc.)
Highlighted severe weather threats:
- Tornado potential: Medium
- Maximum hail size: Up to 6 cm
- Peak wind gusts: Up to 120 km/h
- 24-hour rainfall: More than 200 mm
HIGH risk has been issued for northern and northwestern Italy and southern Switzerland. The threat includes severe damaging winds, large to very large hail, torrential and excessive rainfall with flash floods, and tornadoes.
MDT/ENH risks have been issued for areas surrounding the HIGH risk area, including south and eastern France, central Switzerland, west-central Austria, part of Slovenia, northwest Croatia, and central Italy, with a threat for severe winds, large hail, and torrential rainfall. The expected storm coverage is forecast to be lower than inside the highlighted purple risk area.
Ahead of an emerging frontal system from the west, powerful south-westerlies aloft are advecting high moisture from the central Mediterranean region towards the Alpine region. High dewpoints will result in moderate to locally extreme instability, with MLCAPE reaching 2000 to 3000 J/kg over the Tyrrhenian, Ligurian, and Adriatic Seas.
At the same time, ample wind shear is also overspreading the region, thanks to the intense jet stream aloft. Therefore, a strong forcing develops near the left-exit region of the jet.
A combination of intense wind shear and high instability will lead to a volatile environment with the explosive development of severe thunderstorms from early Thursday onwards. Training multicell thunderstorms are expected as a primary mode, pushing high moisture in a high PWAT (42-45 mm) environment into the complex terrain of northwest Italy and south Switzerland. Extremely intense rainfall is forecast.
This will lead to excessive rainfall within 6 – 12 hours during the day, bringing rainfall accumulations into the 150-200 mm range across a wide area, possibly even close to 300 mm per some high-resolution models. Dangerous flash floods could occur if these predictions are accurate.
In addition, some weather models also hint at supercell thunderstorms forming across the northern portions of the Po Valley, from central Piedmont to Lombardy and Veneto regions. These storms are supported by strong shear and moderately strong CAPE along the sharp convergence zone between the Adriatic moist influx from the east and the Apennines dryline from the south-southwest.
East-northeast low-level flow hints at tornadic supercells if they form on the plains. The tornado threat is maximized from central Lombardy to Veneto, where the highest storm-relative helicity and low-level shear will be present.
Given the high wind shear and instability combined, most thunderstorms will rapidly become severe, with threats ranging from large, wind-driven hail to severe, damaging winds and torrential rainfall.
Further south across the Ligurian side of the northern Apennines, training cells and possible MCS clusters will also bring an excessive rainfall threat and flash flood potential, including tornadic waterspouts near the coast. There, intense supercells fueled by extreme CAPE and high low-level shear will form.
With the upper wave’s slow progress, storms will tend to merge into large clusters and move further east-northeast during the day across the Alpine region and northern Italy. Activity is forecast to continue into the evening and night hours, reaching northeast Italy, western Slovenia, and northwestern Croatia.
Meteoadriatic, Wxcharts, and WeatherBell provided images used in this article.