Storm Forecast
Valid: Wed 09 Sep 2026 06:00 to Thu 10 Sep 2026 06:00 UTC
Issued: Tue 08 Sep 2026 18:28
Forecaster: TUSCHY

A level 3 was issued for parts of NW Italy and parts of the W-CNTRL Mediterranean mainly for excessive rain, large to very large hail, severe gusts and a few tornadoes. An intense tornado is possible.

A level 2 and 1 surround the level 3s for similar hazards with lowered probabilities.

A level 1 was issued for parts of Poland to the Baltic States mainly for severe gusts, some hail and an isolated tornado event.

A level 1 was issued for part of the Netherlands to NW Germany mainly for some hail, strong gusts and an isolated tornado.

SYNOPSIS and DISCUSSION

An amplifying trough over W/NW Europe progresses E while splitting apart. One piece of energy drops S towards Spain and Algeria as a sharp trough extension, while a progressive lower amplitude trough further N races E and affects CNTRL to NE Europe. Ridging builds downstream and affects E Europe into W Russia.

At the surface, an extensive frontal boundary runs from SW Europe to Italy and further N towards the Baltic States and E Finland. Driven by snoptic-scale dynamics but also by the orography, numerous vortices evolve along that front with latest IFS-ENS guidance pointing towards one near the Balearic Islands and another one over N Italy.

Regarding the severe thunderstorm risk, not much details can be described due to the extensive overlap of intense shear along the boundary with decent MLCAPE to its S. Any evolving wave/depression causes regionally enhanced overlaps with severe to extremely severe possible.

The Balearic Islands and offshore areas to the S/E will see increasing DMC probabilities during the day as the upper trough approaches beyond noon. Point source soundings show MLCAPE in the 2000-3000 J/kg range with 20 m/s 3km and 25 m/s 6km shear. The only issue could be, if dried N-erly LL flow causes more elevated conditions next to the boundary, where SRH values peak.
Despite that, all ingredients point to a potential dangerous setup with both discrete supercells and bowing segments possible. Next to the enhanced risk of large to very large hail (with isolated giant hail now ruled out), damaging gusts (with peaks in excess of 30 m/s) and excessive rain (including dangerous flash flooding for training convective segments), we also point to a substantial tornado risk (including an intense/damaging one). This risk is also pushed by 4-5K positive SSTs (rich BL moisture/low LCLs).
Further S/E of the Balearic Islands, a favorable CAPE/shear space points to a mix of intense discrete supercells or bow echoes and swaths with 30 m/s gusts are possible. If we get a long-lived cluster going, we could also see an MCV event with organized convection next to its core, resembling a small-scale tropical-like feature, also driven by an ongoing impressive marine heatwave.

A level 3 upgrade was performed for the corridor, where we expect numerous severe supercells to merge into a damaging progressive MCS/derecho event. As mentioned we even cannot rule out an intense positive PV anomaly within a growing MCV to build down to the surface and evolving into a small-scale tropical-like system, bringing extreme conditions to Sardinia during the night.

N/N-CNTRL Italy will see numerous waves of (extremely) severe as cold front passage gets blocked by the orography, offering all day long the influx of a very moist and unstable airmass into the level 2/3 areas. Numerous eastward racing clusters cause a temporal/regional BL stabilization, before moisture recovery sets in once again with improving CAPE.

Any thunderstorm in this level areas will see favorable conditions for updraft organization with a tornado, heavy to excessive rain, large to very large hail and damaging gust risk. Complex interaction of residual outflow boundaries with the following round of convection could cause regional foci for numerous extreme events like an intense tornado due to local better SRH. Expect organized DMC all day long.

In addition, back-building convection could bring torrential rainfall amounts for parts of Tuscany into Liguria but also from Lombardy to Emilia-Romagna and later during the night also along the NE Adriatic Sea. Favorable influx of very moist/unstable air atop 4-5K positive SSTs with orographic interaction could result in a few damaging flash flood events. Tuscany f.ex. could see a dangerous overnight flash flood setup but also favorable tornado conditions as intense pre (cold) frontal convergence meets a very moist and unstable airmass.

The complex interaction of so many thunderstorms kept this event mostly in an high-end level 2. A level 3 upgrade however was performed for far NW Italy, mainly to highlight both the augmented tornado risk but also the nocturnal flash flood/tornado setup. Despite that, an intense tornado is also possible in the broad level 2 area.

Further NE along that boundary (Baltic States), MUCAPE up to 1000 J/kg overlaps with decent LL and DL shear and we expect a few rotating thunderstorms to erupt along the boundary while racing NE. The focus for maximized severe resides along those frontal segments, where no dried BL flow undercuts the front. Hail, strong to severe gusts and a tornado risk exists with this activity mainly during the afternoon/evening hours.

... The Netherlands and far NW Germany ...

A passing sharp surface trough/vortex creates a favorable overlap of up to 500 J/kg SBCAPE and enhanced LL shear/SRH. A few organized thunderstorms could bring some hail, strong gusts and an isolated tornado with lowered LCLs during the daytime hours.