Storm Forecast
Valid: Thu 20 Aug 2026 06:00 to Fri 21 Aug 2026 06:00 UTC
Issued: Wed 19 Aug 2026 21:02
Forecaster: PUCIK
A level 3 was issued across N Italy mainly for large to very large hail, damaging wind gusts, tornadoes, and heavy rainfall.
A level 2 was issued in a large belt from Spain to S Poland mainly for large to very large hail and damaging wind gusts.
A level 2 was issued for E Morocco and W Algeria mainly for large to very large hail and damaging wind gusts.
A level 1 was issued from N Spain through SE France towards S Germany, S Poland and Belarus/Ukraine mainly for large hail and severe wind gusts.
A level 1 was issued across Netherlands and N Germany mainly for tornadoes.
A level x was issued across (areas) for (hail|tornadoes|wind gusts|extreme rainfall). (repeat for each level area)
DISCUSSION
A combination of a broad belt of strong southwesterly flow, a wavy frontal boundary, and abundant lower tropospheric moisture ahead and south of the boundary will result in an unusually large area of potential severe weather. This area will extend from Spain into Ukraine and Belarus with the highest severe weather risk from the Balearic Sea to N Italy.
... N Italy to Slovenia ...
A potentially high-end severe weather situation is forecast in this area, with a risk of numerous supercells and linear segments capable of all severe weather hazards, with risk running from late morning into late night hours.
Several storms will likely exist over the area, the most likely locations being the Ligurian Gulf and NW Alps. Early morning activity may affect the locations of the highest severe weather risk throughout the day. By 12 UTC, models simulate 1500 to 3000 J/kg over the area, combined with 15 to 25 m/s of 0-6 km bulk shear. Three main initiation mechanisms are anticipated: local orography, the dryline over Piemonte expanding S/SE, and the dryline from the Apennines spreading N/NE. Stronger shear and higher CAPE is forecast to the cooler and moister side of the drylines with hodographs enlarging towards the evening hours as the low-level flow ramps up and the WAA regime is enhanced towards the cooler side of the boundaries. A window will exist with surface-based storms and substantial SRH and low-level shear with 0-1 km SRH locally exceeding 150 m2/s2, 0-1 km bulk shear reaching up to 15 m/s and 0-3 km shear up to 25 m/s. Then, towards the night, a switch to the elevated storm mode is forecast, but storms will still tap into substantial CAPE and shear with no decrease in the storm intensity.
A chaotic storm-scale evolution is likely throughout the scenario. ICON-D2 EPS shows numerous strong supercells evolving from late morning into late night over the entirety of Lvl 3 area with storms spreading from Italy towards N Adriatic and Slovenia. Storm coverage will start increasing with the approach of a subtle short-wave trough and with cells interacting along the boundaries. Multiple storm collisions may occur as left- and right- movers interact. The primary severe weather threat will likely depend on the storm-scale evolution. More isolated storm mode will favour very large hail and tornadoes in the evening hours, whereas an upscale growth will elevate the heavy rainfall and severe wind gust risk. Heavy rainfall risk should not be overlooked in this scenario with local accumulations up to 200 mm possible especially over Liguria and Swiss/Italy border.
... Massif Central to W Alps ...
Several rounds of storms will be possible starting in early morning hours and lasting to late evening or night. With 0-6 km bulk shear of 15 to 25 m/s and MLCAPE between 1000 and 2000 J/kg, some supercells are likely, with a threat of large-to-very-large hail and severe wind gusts. The eventual occurrence of early morning storms may reduce the severe weather threat for the afternoon hours. Should at least some diurnal heating occur, enabling the buildup of CAPE, coverage of severe weather should be sufficient to warrant a Lvl 2.
... W Mediterranean towards NW Italy ...
The main player here will be a sharp short-wave trough that will be located over S Spain at 12 UTC and will eject NE-wards. A rapid increase in storm coverage is anticipated over the Balearic Sea once the short-wave trough reaches the area. Synoptic-scale lift and an ill-defined boundary will deepen the low-level moisture with rapid initiation of numerous storms. MUCAPE values above 3000 J/kg are likely with 0-6 km bulk shear between 15 and 20 m/s. Heavy rainfall, large to very large hail and damaging wind gusts will be likely with stronger storms. An upscale growth seems likely with storms tracking towards the area of the greatest synoptic-scale lift associated with the trough. Late-night arrival of storms over Corsica, N Sardinia or NW Italy will bear a high risk of severe wind gusts and very heavy rainfall. Lvl 3 was considered, but was not issued due to the absence of 0-6 km bulk shear well above 20 m/s and some uncertainties in the timing of the MCS. Nevertheless, a potentially high-end situation is in store for this area.
... Austria to S Poland ...
The situation will probably begin with several supercells forming over the Alps or over the N Alp forelands, travelling east with threats of large to very large hail and severe wind gusts. Storms will form in an environment of 1000 to 2000 J/kg of MLCAPE and around 0-6 km bulk shear. Higher-resolution models hint on an upscale growth as storms arrive to E Austria. With pressure falls on a subtle frontal wave, more southerly wind direction will push storms further north, with a linear segment likely travelling across E Czechia/W Slovakia into S Poland. Strong shear reaching 15 to 20 m/s in both 0-3. and 0-6 km layers suggests favourable conditions for linear segment maintenance and enhanced risk of severe wind gusts. Isolated supercells capable of large hail and severe wind gusts will be possible preceding the linear segment, forming on the local orography of the Carpathians. Storms may continue well overnight and travel to eastern Poland, still capable of isolated severe weather.
... Switzerland, S Germany, W Czechia ...
CAPE will be lower and skinny here, but given 0- 6 km bulk shear will reach 20 to 25 m/s with 0-3 km shear up to 20 m/s; a couple of fast-moving, low-topped supercells are likely, with large hail and severe wind gust risk. Given fast motion of supercells, isolated swaths of wind gusts around 30 m/s are possible.
... Netherlands to N Germany ...
A combination of a low LCL environment, substantial 0-3 km CAPE, and 0-1 km shear around 10 m/s points to an elevated tornado threat with supercells that may form given 15 to 20 m/s of 0-6 km bulk shear.
... Morocco to Algeria ...
A couple of intense supercells may form in an environment of moderate MLCAPE around 1000 J/kg, high LCLs and up to 30 m/s 0-6 km bulk shear, with threats of large to very large hail and damaging wind gusts.
