Storm Forecast
Valid: Thu 28 Aug 2025 06:00 to Fri 29 Aug 2025 06:00 UTC
Issued: Wed 27 Aug 2025 21:33
Forecaster: PUCIK
A level 1 was issued across W France mainly for severe wind gusts and tornadoes.
A level 2 was issued across Catalonia and the Balearic Sea mainly for large hail, severe wind gusts and heavy rainfall.
A level 1 was issued across NE Spain mainly for large to very large hail and severe wind gusts.
A level 1 was issued across NE France, E BENELUX, W Germany and Denmark mainly for marginally large hail and severe wind gusts.
A level 3 was issued across N Italy mainly for heavy rainfall, damaging wind gusts, large to very large hail and to the lesser extent for tornadoes.
A level 2 was issued from SE France to N Italy mainly for large to very large hail, damaging wind gusts, heavy rainfall and to the lesser extent for tornadoes.
A level 2 was issued across NW Austria mainly for large to very large hail and severe wind gusts.
A level 1 was issued across NE Germany and NW Poland mainly for heavy rainfall and to the lesser degree fo large hail and severe wind gusts.
A level 1 was issued across E Algeria and extreme W Tunisia for severe wind gusts and large hail.
DISCUSSION
... NE Spain, Catalonia, parts of the Balearic Sea ...
Elevated storms will be ongoing across Catalonia in the morning hours, possibly spreading over the Sea throughout the day. Environment will be characterized by over 1000 J/kg of MUCAPE combined with over 20 m/s of "effective" deep-layer shear. Large hail and heavy rainfall will be primary threat with isolated severe wind gusts not ruled out. Further south, initiation will be questionable with dry air in the mid-troposphere ovespreading the region. A dry-line will setup inland and on the slopes of the topography towards Valencia with MLCAPE reaching up to 2000 J/kg and strong vertical wind shear. However, initiation is highly uncertain. Will include the region in Lvl 1 with highly conditional threat of large to very large hail and severe wind gusts.
Further attention needs to be paid over the Balearic Sea, where some models indicate storms building towards the south towards higher CAPE, perhaps reaching as far as Mallorca. With increasing CAPE, the storms would have higher likelihood of both very large hail and stronger wind gusts. Such development must be monitored. Overall, the severe weather threat will start diminishing after 15 UTC.
... W France ...
A fast-moving short-wave will cross the region towards Friday morning with environment characterized by marginal CAPE and strengthening low-level flow and low-level shear. Expect fast-moving linear segments and perhaps a couple of low-topped supercells which may cause one or two tornadoes and marginally severe wind gusts.
... NE France to E BENELUX, W Germany and Denmark ...
Scattered storms will form ahead on a cold front that will move E. Forecast profiles reveal modest MLCAPE ranging from 500 to 1000 J/kg and decent 0-6 km bulk shear of around 20 m/s. Low-level shear will be rather weak and with no curvature in the hodographs, predicted SRH values remain mostly below 100 m2/s2 in the 0-3 km layer. We expect a mix of multicells and short-lived splitting supercells with weak rotation. Stronger cells may be capable of marginally large hail and severe wind gusts.
... SE France to N Italy ...
A complicated forecast with some potential for higher-end intensity of severe storms will unfold over the area. Plentiful storms will be ongoing across SE France and NW Italy in the morning hours with threats of heavy rainfall and also large to perhaps very large hail close to the coast, where substantial CAPE and effective shear are forecast. An extremely heavy rainfall event will continue on the Swiss/Italian border with storms training across the area at least till the afternoon hours. Overall rainfall sum for the whole rain period may thus exceed 300 mm locally.
Towards the afternoon hours, a convergence zone will set up over Italy in between of easterly flow from the Adriatic Sea and southerly drier flow emerging from the Apennines. North of the convergence zone, poor low-level lapse rates with specific humidity of around 14 g/kg and MUCAPE reaching 1000 to 2000 J/kg. As low-level flow backs to northeasterly, strongly curved hodographs are anticipated north of the convergence zone with 0-1 km SRH exceeding 300 m2/s2 and 0-6 km bulk shear around 25 m/s. Models are not in agreement whether the storms developing in this zone will be elevated or not and thus whether the low-level shear will be effective for them. Nevertheless, even in elevated mode, well-organised linear segments and supercells are expected.
Potential will exist for some long swaths of large to perhaps even very large hail and damaging wind gusts in these storms. In case surface-based storms develop in this corridor, a strong tornado could occur given the impressive low-level kinematics. The overall environment could suffice for a Lvl 3. However, the high-resolution, convection-allowing models and their ensembles do not show agreement concerning development of intense supercells. Some of the models show development mostly over the mountains with only short and moderately intense tracks of updraft helicity. While a considerably uncertainty remains in how this scenario plays out, a small Lvl 3 is introduced in the region, where multiple waves of rotating storms are possible beginning in the morning hours and lasting till the night.
... SE Germany, NW Austria, SW Czechia ...
A convergence zone is forecast to set up over NW Austria along a dry line created by the dry downslope wind behind the Alps. North of the dry-line a local sweetspot of MLCAPE reaching up to 2000 J/kg is forecast, combining with enhanced shear reaching up to 20 m/s in the 0-6 km layer. As a cold front approaches, mesoscale lift may become strong enough to initiate one or two supercells capable of large to very large hail and severe wind gusts. Such evolution is not certain at all with only a couple of members of high resolution ensembles simulating such development. Nevertheless, a small lvl 2 is introduced to highlight the most likely corridor of severe weather in this rather typical setup over the region. Further N and W, initiation will be tied to the cold front passage with storms developing on the cooler side and quickly experiencing decrease in CAPE. Rather marginal risk of heavy rainfall and large hail are forecast here.
... NE Germany to NW Poland ...
Models simulate impressive kinematic environment ahead of wave developing on an ill defined cold front featuring strongly curved hodographs with over 300 m2/s2 of SRH in the 0-3 km layer and 20 to 25 m/s of 0-6 km shear. Skinny CAPE profiles are simulated but with solid MLCAPE values reaching around 1000 J/kg. Such combination points to a rather high likelihood of severe weather with any storm that initiates. However, models do not simulate any storms ahead of the front. Storms are forecast to inititiate in the wake of the front in marginal MUCAPE environment with dominance of heavy rainfall threat perhaps mixed with severe wind gusts should any storm come closer to the boundary itself. Nevertheless, we recommend to monitor this area closely to track any possibility of storm development ahead of the cold front. Such storm would quickly become supercell capable of severe weather.
... Algeria to Tunisia ...
Forecast profiles reveal well mixed and deep boundary layer combined with about 1000 J/kg of MLCAPE and 15 to 20 m/s of 0-6 km bulk shear. Storms forming in these conditions would organise into supercells or strong multicells capable of large hail and damaging wind gusts. Coverage of the storms is uncertain but Lvl 1 seems warranted for the area.
