Storm Forecast
Valid: Wed 27 May 2026 06:00 to Thu 28 May 2026 06:00 UTC
Issued: Tue 26 May 2026 21:02
Forecaster: PUCIK
A level 1 was issued across NW France and SW UK mainly for large hail and severe wind gusts.
A level 2 was issued for NE Italy and W Slovenia mainly for large hail, severe wind gusts and heavy rainfall.
A level 1 was issued for NE Italy, Slovenia, S Austria, N Croatia mainly for large hail, severe wind gusts and heavy rainfall.
A level 1 was issued for S Poland, E Slovakia, W Ukraine, E Belarus and N Romania mainly for severe wind gusts.
A level 2 was issued for central Ukraine mainly for damaging wind gusts and to a lesser extent for tornadoes and marginally large hail.
DISCUSSION
... NW Iberia ...
An uncertain forecast situation will unfold across the region with large differences in the convective coverage across the region. With no synoptic-scale support or frontal zone, convective initiation will be confined to orography or local convergence zones. High LFCs and dry layers near and above the LFC yield rather low probability of initiation. That said, GFS and ECMWF trigger storms over several locations. Inverted-V profiles will yield isolated severe wind gust threat.
NW France to S/central UK ...
Heatwave continues across the area with a subtle frontal zone across central UK. Across it, some mesoscale lift is forecast thanks to the warm air advection. Further south, over NW France, some models suggest a shallow dryline boundary that may provide some lift as well. While abundant CAPE will be available across the region with moderate vertical wind shear, convective initiation is highly questionable. One of the reasons is presence of dry layers in the mid-troposphere above the LFC. Should any sustained storm form over France and southern UK, it will bear risk of large hail and severe wind gusts thanks to the high CAPE, high LCL environment. Towards the night hours, strong low-level shear is forecast with curved hodographs, but storms will transition into elevated mode with the highest chances across the warm wave over central UK.
... SW Italy ...
A small area with locally favorable conditions for large hail will be present across SW Italy with MLCAPE above 1000 J/kg and 0-6 km bulk shear of around 15 m/s. Isolated coverage is forecast.
... the Alps and their S flanks ...
In prevailing N-ly flow, storms are forecast to initiate across the main Alpine ridge and then propagate towards the lowlands. Environment will be characterized by specific humidity of 12 to 14 g/kg across N Italy and around 10 g/kg across Slovenia and Croatia, combined with 7 to 7.5 K/km lapse rates. MLCAPE values will reach 1 to 3 kJ/kg, overlapping with 10 to 15 m/s of 0-6 km vertical wind shear. The shear may be locally enhanced if stronger southerly upslope winds form compared to the model expectations. A mix of multicell clusters and transient/marginal supercells is forecast with threats of large hail and severe wind gusts. The risk of severe wind gust will increase towards Slovenia and Croatia, where higher LCLs are forecast, the risk of hail around 5 cm in diameter will be present especially in lvl 2, where the ICON D2 EPS simulates the highest risk of marginal supercells. Heavy rainfall is most likely in the early period with storms development anchoring at first to the local terrain. Further development will be dictated by the movement of outflow boundaries and storms may even reach Bosnia in the evening.
... S Poland, N Slovakia to Ukraine ...
Modest low-level moisture with specific humidity up to 10 g/kg will overlap with lapse rates of around 6.5 K/km, resulting in skinny CAPE profiles and MLCAPE in between of 500 to 1500 J/kg, increasing towards Ukraine. Synoptic-scale lift will be mostly absent with mesoscale lift being provided by a surging cold katafront. Convective coverage is questionable. One one hand, it seems that rather shallow lift will be present along the front. On the other hand, the front will surge south fast and may result in cell clustering along it. Given very strong vertical wind shear, with values between 15 to 25 m/s in the 0-3 to 0-6 km layer, a mix of well-organised linear segments and supercells is forecast. Forecast hodographs are mostly straight with strong mean flow and 0-1 km shear reaching 10 to 20 m/s. The main threat will be severe wind gusts that may exceed 30 m/s especially within the designated Level 2. Tornado threat will increase towards the eastern edge of Level 2 and E Ukraine/Russia in general, where more curved hodographs are forecast with 0-500 m SRH locally exceeding 100 m2/s2. Marginally large hail also can't be ruled out with the stronger updrafts.
