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: 02/09/2025 06 UTC – 03/09/2025 06 UTC
Issued by: Severe Weather Europe
Forecaster: Marko Korošec
SUMMARY
This event follows a significant, record-breaking rainfall event last Friday in southwestern Slovenia. According to the high-resolution weather models, another potentially high-end flooding risk event is coming up on Tuesday, September 2nd, 2025.
A deep upper-level trough formed from the ex-hurricane Erin remains fully mature over western Europe and the North Atlantic. Its secondary vorticity maximum will again expand into the northern Mediterranean and the Alpine region this Monday into Tuesday. This will result in widespread thunderstorm activity over northern Italy and the Alps, gradually spreading east into the North Adriatic region.
On Tuesday, a rather volatile set of environmental conditions combined over the same region as last Friday, supporting severe thunderstorms with a trailing-cell effect thunderstorms. Intense, excessive rainfall with a flooding threat is forecast, with additional threats of severe winds, large hail, and a few tornadoes possible.
Multiple rounds of slow-moving severe thunderstorms are forecast from the North Adriatic into northeast Italy, west-southwest Slovenia, and northwest Croatia from early Tuesday morning through Tuesday night.
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 90 km/h
- 24-hour rainfall: More than 200 mm
HIGH risk has been issued for extreme northeast Italy, west-southwest Slovenia, and northwest Croatia. The threat includes extreme, torrential, and excessive rainfall with flash floods, severe, damaging winds, large hail, and tornadoes.
MDT/ENH risks have been issued for areas surrounding the HIGH risk area, including north and central Italy, south-western Austria, southern Switzerland, west-central Austria, central and south Slovenia, and north-northwest Croatia, 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.
This outlook focuses on Tuesday, when a significant severe weather event is expected for the North Adriatic region. The upper wave axis will emerge over the Alps into the northern Mediterranean. Robust thunderstorms are expected across northeast Italy into western Slovenia and northwest Croatia. With intense training cells leading to excessive rainfall that will support damaging flash floods. Additional storms will also follow in central Italy.
Above: Video animation of the convective storm’s development across central Europe from Tuesday morning through Wednesday morning, September 2nd to 3rd, 2025.
For this reason, HIGH + MDT risks have been placed across the North Adriatic region, with highlighted areas where the most robust severe weather and flooding threat will develop on Tuesday.
SYNOPTIC OVERVIEW
A large upper-level trough is located over the North Atlantic and Western Europe. Its secondary wave is emerging into central Europe and forecast to deepen considerably on Tuesday. This will establish a typical volatile setup for the north Mediterranean and the North Adriatic region, leading to an extreme risk of flooding.
On Tuesday, a large Omega blocking pattern is established to the east and north, providing strong upper-level wind maximum over the highlighted area.
At the surface, an extensive low-pressure system is centered over western Europe, with a shallow secondary low forming in the north Mediterranean and central Europe, in response to the upper wave axis moving into the Alpine region aloft.
This results in a frontal system progressing west to east over central Europe, with the cold front moving into the North Adriatic region during the day.
WEATHER FORECAST DISCUSSION – Tuesday, September 2nd 2025
+++ Weather forecast for Italy, Slovenia, Croatia, Switzerland, and Austria +++
With the emerging frontal wave from the west, powerful south-westerlies aloft are advecting high moisture from the central Mediterranean towards the Alpine region.
At the same time, ample wind shear is also overspreading the region, thanks to the intense jet stream aloft. Therefore, a strong upper-level forcing develops near the left-exit region of the jet and supports widespread lifting.
A combination of intense wind shear and strong instability, mainly when parallel to the frontal zone, will lead to a volatile environment with the explosive development of severe thunderstorms from early Tuesday morning onwards.
Training multicell and supercell thunderstorms are expected as a primary mode, pushing high moisture in a high PWAT (42-45 mm) environment into the complex terrain of northeast Italy, west-southwest Slovenia, and northwest Croatia. Extremely intense rainfall is forecast.
This will lead to excessive rainfall within 6 – 12 hours during the day, bringing rainfall accumulations into the 100-200 mm range across a wide area and possibly even more than 300 mm locally, per some high-resolution models.
If these predictions are accurate, dangerous flash floods could occur, particularly over southwestern Slovenia and northwest Croatia.
The background mechanism supporting such a robust environment lies in the substantial low-level moist influx across the Adriatic Sea towards the north, where strong forcing and shear will support explosive thunderstorms with intense rainfall.
Both low-level shear and helicity hint at supercell thunderstorms along the sharp convergence zone, which could lead to tornadoes and waterspouts. Those are most likely to form in the HIGH-risk and southern portion of the MDT-risk areas.
The tornado threat is maximized along the coast of northeast Italy to coastal southwest Slovenia and over the Istra peninsula to Kvarner Bay, Croatia, where the highest storm-relative helicity and low-level shear will be present.
High dewpoints will result in moderate to locally strong instability, with MLCAPE reaching around 2000 J/kg over the Adriatic Sea.
Given the high wind shear and instability combined, most thunderstorms will rapidly become severe, with threats ranging from intense to extremely intense rainfall, large hail, severe winds, and tornadoes/waterspouts.
Further south across the Ligurian and Tyrrhenian side of central Italy and the Apennines, training cells and a possible MCS cluster will also bring widespread thunderstorm activity, with an excessive rainfall threat and flash flood potential. Some tornadic waterspouts near the coast will be possible, as storms will be fueled by strong CAPE and high low-level shear along the coast.
With the upper wave’s eastward progress during the day, storms will tend to merge into clusters and move further east from the North Adriatic region into the northwest Balkan peninsula towards Tuesday night. Activity is forecast to weaken gradually overnight to Wednesday.
Wetterzentrale, Meteolab, Wxcharts, and WeatherBell provided images for use in this article.
See also: Severe Weather Forecast / Outlook for Europe – August 28th, 2025