Storm Forecast
Valid: Fri 28 Aug 2026 06:00 to Sat 29 Aug 2026 06:00 UTC
Issued: Thu 27 Aug 2026 22:31
Forecaster: PUCIK
A level 3 was issued across S Germany, NW Austria, extreme S Switzerland, and N Italy mainly for destructive wind gusts and large to very large hail.
A level 2 was issued from SE France to SW Czechia mainly for destructive wind gusts and large to very large hail.
A level 2 was issued from NE France through parts of BENELUX to N Germany mainly for large hail, severe wind gusts and heavy rainfall.
A level 1 surrounds the level 2s for more isolated severe weather.
DISCUSSION
... SE France to SW Czechia ...
Several destructive storms are likely to form within the corridor, with primary hazards being damaging wind gusts and large to very large hail.
Ahead of a deep trough at mid to upper troposphere, strong mid-tropospheric flow will overspread the area, and a short-wave trough is forecast to cross from France to northern Italy with a cold front approaching the area. The whole area will be under strong vertical wind shear with 0-6 km bulk shear between 20 and 35 m/s, supporting strong supercells and/or bow echoes.
The situation will start with morning storms over SE France and Switzerland that will quickly spread towards S Germany and perhaps further into W Czechia. Expect destructive wind gusts and large hail with the storms. In the afternoon hours, another round of storms is forecast.
The first region will be S Germany/N Austria in a classic pre-Alpine setup with the advancing cold front and a convergence along the northern flanks of the Alps. A local CAPE maximum is simulated in a narrow belt along the convergence zone with MLCAPE exceeding 1500 J/kg. Along and just behind the cold front, an increase in the 0-3 km shear and 0-3 km SRH is forecast. High-res models simulate several intense supercells or short linear segments that would be capable of severe to extremely severe wind gusts and large to very large hail. Level 3 denotes where the extremely severe weather is most likely concerning the pre-convective environment and simulated UH tracks, but there is some difference among the models regarding the exact location and timing of the most intense storms. Storms will spread towards N Austria and SW Czechia and eventually weaken as CAPE decreases.
An even more impressive environment is forecast across the N Italy, where MLCAPE of 2000 to 4000 J/kg will overlap with 25 to 35 m/s of 0-6 km bulk shear and around 20 m/s of 0-3 km shear. Hodographs will remain mostly straight. Level 3 is issued where the high-resolution models simulate supercell development, i.e. the Ticino area and further east. Outside of here, few if any, storms are simulated by the models with initiation provided by an upslope flow over the Alps. The most important message is: any sustained storm developing across N Italy will likely become a supercell capable of destructive hail and wind gusts.
... N France to BENELUX and N Germany ...
Another corridor of severe weather will be associated with another short-wave trough that will rapidly cross on the forward flank of the deep long-wave trough. Ahead of the surface cold front, MLCAPE in the range of 700 to 1500 J/kg is forecast. With rather poor mid-tropospheric lapse rates, CAPE profiles will not have very high values of buoyancy in the upper troposphere. As the trough approaches, deep-layer shear will increase, surpassing 25 m/s in the 0-6 km layer. Straight hodographs will result in more marginal SRH values, but overall, the kinematic environment will be supportive of splitting supercells and well-organised linear segments. Compared to areas in the south, high-res models do not show as intense supercells, but coverage of severe weather should still be enough to warrant a Level 2. Expect a combination of large hail, severe wind gust risk, and locally heavy rainfall.
