Storm Forecast
Valid: Tue 23 Sep 2025 06:00 to Wed 24 Sep 2025 06:00 UTC
Issued: Mon 22 Sep 2025 15:00
Forecaster: TUSCHY
A level 2 was issued for the Gulf of Venice mainly for excessive rain.
A level 2 was issued for Lombardy and surroundings mainly for large hail, severe gusts, excessive rain and a tornado risk.
A level 1 surrounds the level 2 and extends into N Algeria/Tunisia mainly for some hail, isolated large (N-Algeria/Tunisia), a few excessive rain and gust events and an isolated tornado risk.
SYNOPSIS
The finalized cut-off process over France turns into an high-over-low pattern as heights increase substantially over the Norwegian Sea into Norway. In the meantime, a blocking anticyclone persist over SE Europe and faces a trough over E Scandinavia. This pattern supports the influx of a drier airmass deep into W/CNTRL Europe, whereas a plume of rich moisture still resides over the CNTRL Mediterranean. A wavy boundary runs from SE Spain to Austria into W Russia, which spreads out an extensive warm sector over Italy and surrounding areas.
DISCUSSION
... Gulf of Venice ...
Local WRF data and LAMs resolve a diffuse LL depression over N Italy, which shifts E/SE towards the Adriatic Sea into the overnight hours. An accompanying cold front with a sharp wind shift pushes E/SE.
The prefrontal warm sector features the best ingredients within the level 2 area, especially near a zonal/coastal convergence zone. The periphery of this convergence zone offers a confined space supportive for supercell development, as 2000 J/kg MUCAPE overlap with 15 m/s DLS. A broadening of the LL hodographs with increasing SRH and strengthening 0-3 km shear point to the chance for a few intense supercells with all kind of severe. EPS data has numerous members, which produce copious amounts of rain along the coastal areas in case the wind shift remains within the vicinity of the coasts. Hence an excessive rain risk with flooding issues is present. A tornado risk is also present next to isolated large hail and gusts.
Betimes, a SE-ward shifting V-shaped cluster brings heavy rain and a coastal tornado risk SE towards W Croatia, but its progressive nature keeps this event in a level 1.
... Lombardy and surroundings ...
Another volatile setup evolves more inland, where a marine airmass advects beneath steepened mid-level lapse rates downstream of the W Apennines. A confined area of 1000-2000 J/kg MUCAPE is forecast, which evolves beneath an intense mid/upper jet (DLS 25-30 m/s and 15 m/s 0-3 km shear). Although not impressive, enough SRH is forecast with the E-erly BL flow regime, so initiating cells have some time to remain semi-discrete and become organized supercells. A tornado risk is present in a low LCL setup next to isolated large hail and severe gust. Betimes, clustering turns this more into a messy heavy rain event.
... Level 1 area ...
A broad level 1 area surrounds both level 2 areas all the way into N Africa. Within the brisk SW to S-erly flow regime, embedded IPV maxima serve as foci for temporarily and regionally enhanced CI, next to mesoscale boundaries or the orography itself. The CAPE/shear space supports organized convection, although the final supercell risk depends more on local effects like internal dynamics and strongly deviating motions along boundaries. All kind of severe is possible but restricted to local places. Overall there is an augmented large hail risk towards Algeria/Tunisia with more of an heavy rain and isolated tornado risk along the Italian coasts. Once again, missing foci for maximized severe coverage preclude any upgrades for now.
.. Far E France into far W Germany ...
A structuring deformation band becomes the main focus for heavy rain during the evening into the overnight hours. Embedded convective elements could bring isolated heavy rain but modest background moisture with PWs in the 20-25 mm range preclude a level upgrade for now.
