Severe weather outlook – forecast across Europe. This forecast highlights areas of organized severe weather, along with risk levels and severe weather threats across Europe.
SEVERE WEATHER OUTLOOK
Valid: 09/09/2026 06 UTC – 11/09/2026 06 UTC
Issued by: Severe Weather Europe
Forecaster: Marko Korošec
SUMMARY
*** A significant two-day severe weather outbreak is forecast across portions of western and northern Mediterranean from Wednesday through Friday afternoon this week. Moderate to extreme instability and strongly sheared environments combine for widespread thunderstorm activity with large to giant hail, severe winds, tornadoes, and damaging flash-flood potential from the Balearic Islands to southern France, northern Italy, and the Alps on Wednesday. Followed by another day of widespread severe thunderstorm activity across Northern Italy, Slovenia, Croatia, and across central Italy and the Central Adriatic region.***
A large, deep upper-level trough has emerged into western Europe and is moving east, with a strong blocking High to its east collapsing as it moves into Eastern Europe. Between these large-scale features, a strong southwesterly jet stream is providing ample wind shear, while the air mass beneath it is extremely humid, resulting from the historic marine heatwave over the Mediterranean.
This outlook focuses on Wednesday’s and Thursday’s evolution, with a significant severe weather event forecast along the racing cold front from the Alpine region to the Balearic Islands on Thursday and across north-central Italy, Slovenia, Croatia, and the Adriatic on Friday.
Robust and destructive thunderstorms are expected from Wednesday morning through Friday afternoon.
Above: Video animation of the convective storm’s development across Central Europe and the Mediterranean from Wednesday through Friday night, September 9th and 10th, 2026.
For this reason, HIGH + MDT risks have been placed across portions of the Western and Northern Mediterranean region, with highlighted areas where the most robust severe weather threat will develop on both days. The threat includes enhanced potential for severe damaging winds, destructive flash floods, tornadoes, and very large to giant hail (6-10 cm or larger).
SYNOPTIC OVERVIEW
This week’s weather pattern over Europe shows the underlying risk to the Balearic Islands, Italy, and the north-central Adriatic region on Wednesday and Thursday. As a deep wave over western Europe emerges further east and cuts off into the Northern Mediterranean, it creates a significant pressure and temperature gradient against the departing upper-level ridge to the east.
This significantly amplifies southwesterly jet-stream winds from eastern Spain across the northern Mediterranean, providing violent wind shear.
This brings a frontal system moving across Central Europe into the Mediterranean, with the cold front moving west to east from France and the Alps into Italy, Slovenia, and Croatia from Wednesday morning through Friday night.
WEATHER FORECAST DISCUSSION – Wednesday, September 9th
+++ Weather forecast for Spain, Italy, Austria, Slovenia, and Croatia +++
Explanations for abbreviations (TSTM, SLGT, ENH, etc.)
Highlighted severe weather threats:
- Tornado potential: High
- Maximum hail size: More than 8 cm
- Peak wind gusts: Up to 120 km/h
- 24-hour rainfall: More than 150 mm
HIGH risk has been issued for the Balearic Islands, southern Corsica and Sardinia, Tuscany and Liguria for severe thunderstorms. The threat includes severe damaging winds, very large hail, torrential and excessive rainfall with destructive flash floods, and tornadoes.
MDT/ENH risks have been issued for areas surrounding the HIGH risk areas, including most of the western and northern Mediterranean and the Alpine region into the northwestern Balkans, with a threat of severe winds, large hail, and torrential rainfall. Storm coverage is expected to be lower than inside the highlighted purple risk area.
Ahead of an emerging frontal system from the west, strong westerlies aloft are advecting high moisture from the central Mediterranean into the Balearic Islands and around Italy and the northern Adriatic. Given the ongoing historic Mediterranean marine heatwave, high dewpoints near or above 25 °C will result in moderately strong to locally extreme instability, with MLCAPE reaching 3000 to 4000+ J/kg over the western, northern, and central Mediterranean.
At the same time, ample wind shear is also overspreading the region, thanks to the intense mid-level jet stream aloft. As a result, strong forcing develops near the jet’s left exit region and along the cold front.
A combination of strong wind shear and extreme instability will create a volatile environment, with explosive development of severe thunderstorms from early Wednesday, starting over the Balearic Islands, Ligurian Bay, and the rest of northwestern Italy, gradually spreading east through the afternoon, where southerly moist winds will transport high dewpoints and fuel explosive storms. Isolated but intense supercells are expected as the primary mode, supporting rapid development of severe threats, very large to giant hail, severe destructive winds, and torrential rainfall with flash floods.
Strong southeast low-level flow also hints at tornadic supercells. The tornado threat is maximized across the Balearic Islands portion of the HIGH risk area, where the highest storm-relative helicity and low-level shear will be present along with extreme CAPE. Storms will move east-northeast through the afternoon and may merge into large clusters, with destructive winds as the primary threat, as they approach southern Corsica and Sardinia.
The Ligurian and Tuscan coastal areas were highlighted for potential tornadic supercells, with strong southeast flow along the western side of the Apennines. In addition, intense storm clusters will dump significant rainfall into interior areas, with rainfall sums peaking above 200 mm locally and triggering dangerous flash floods.
Another area of enhanced storm activity is expected over the Po Valley if the surface low over the northern Italian plains forms and backs the winds from the moist Adriatic Sea. This would fuel storms with extreme instability, combined with strong low-level shear, supporting intense supercells with giant hail, tornadoes, and severe damaging winds.
Through Wednesday night, storms will merge into large cluster(s) while continuing northeast across northern Italy and the Adriatic region, reaching western Slovenia and northwestern Croatia toward the evening. Given the high wind shear and strong to extreme instability, large hail, severe damaging winds, and torrential rainfall will be the main threats.
WEATHER FORECAST DISCUSSION – Thursday, September 10th
+++ Weather forecast for Italy, Slovenia, and Croatia +++
Explanations for abbreviations (TSTM, SLGT, ENH, etc.)
Highlighted severe weather threats:
- Tornado potential: Medium
- Maximum hail size: More than 8 cm
- Peak wind gusts: Up to 120 km/h
- 24-hour rainfall: More than 150 mm
HIGH risk has been issued for northeastern Italy, northern Adriatic Sea, western Slovenia, and northwestern Croatia for severe thunderstorms. The threat includes severe winds, very large hail, torrential and excessive rainfall with destructive flash floods, and tornadoes.
MDT risk has been issued for eastern north-central Italy, the Adriatic Sea and Tyrrhenian Sea region, southern Croatia, and western Bosnia for severe thunderstorms. The threat includes severe damaging winds, very large to giant hail, torrential and excessive rainfall with destructive flash floods, and tornadoes.
ENH/SLGT risks have been issued for areas surrounding the MDT risk areas, including most of Italy and the west-central Balkans, with threats of severe winds, large hail, and torrential rainfall. Expected storm coverage is forecast to be lower than within the highlighted purple risk area.
Widespread thunderstorm activity will continue from the previous night with additional storms forming during the day across northern Italy and the northern Adriatic region, supported by extreme instability and amplified wind shear. Intense, slow-moving multicells and supercells will be the primary storm modes before the activity clusters into one or two large convective systems toward the afternoon.
Besides the discrete, intense supercells with damaging winds, tornadoes, and large hail, the greatest concern on Thursday will be significant rainfall that may accumulate as training cells from numerous waves of storms from Wednesday night through Friday midday. This could quickly increase rainfall totals, with some areas reaching 200-300 mm within 36 hours.
After months of severe drought, this significant rainfall will create a dangerous severe weather situation, with potentially destructive flash floods where rainfall totals are highest.
Several high-resolution weather models support this outlook, given the extreme instability and unseasonably high dewpoints in the region. Supported by strong southerly flow across the Tyrrhenian and the Adriatic Seas, tornadoes, including strong ones, will be possible as well.
PivotalWeather provided images used in this article.