Storm Forecast
Valid: Wed 03 Sep 2025 06:00 to Thu 04 Sep 2025 06:00 UTC
Issued: Wed 03 Sep 2025 07:30
Forecaster: PUCIK
A level 2 was issued across NW France, Belgium and Netherlands mainly for (strong) tornadoes and damaging wind gusts.
A level 1 was issued in the surrounding area mainly for tornadoes and severe wind gusts.
A level 2 was issued for S Serbia mainly for large hail, severe wind gusts and heavy rainfall.
A level 1 was issued from N Greece to Romania, Slovakia and S Poland mainly for heavy rainfall and large hail.
A level 2 was issued across NE Turkey and Georgia mainly for large hail and heavy rainfall.
A level 1 was issued from NE Turkey to S Russia mainly for heavy rainfall and large hail.
DISCUSSION
... N France through BENELUX, S UK into NW Germany, Denmark and S Norway ...
A rapidly moving short-wave trough at upper troposphere is forecast to cross the region. The trough will follow passage of a warm front with a weak cold front trailing behind. Within the warm sector, strong increase in the low-level flow is forecast, reaching up to 25 m/s at 850 hPa. Within the warm sector a modestly moist airmass with dewpoints up to 16 deg C and poor lapse rates is forecast, yielding skinny CAPE profiles. Behind the trough, dry intrusion is forecast in mid to upper troposphere, significantly weakening the updrafts at these altitudes. Forecast hodographs show unseasonably strong vertical wind shear concentrated in the lowest 1 km. Strongly curved hodographs are simulated by all models with 15 - 20 m/s of 0-1 km bulk shear and 0-500 m SRH locally exceeding 200 m2/s2. Combined with the mean flow of 25 m/s in the lower troposphere, kinematic environment will be favorable for tornadoes, some of which may be strong, and damaging wind gusts. Risk of both will depend also on the heating ahead of the storms. Should heating remain very limited, poor or absent low-level CAPE may reduce especially the tornado threat. This is the first uncertainty of the situation.
Current expectation is that a mix of low-topped supercells and short linear segments will develop over N France around 9 UTC and rapidly progress NE-ward with the highest risk from France to SE UK and BENELUX in 12 to 18 UTC timeframe. Coverage of storms is the second source of uncertainty with only weak signals in the low-level convergence zones developing around the coastal zones. Current thinking is that isolated to scattered storms will form with coverage increasing towards the UK, where the strongest forcing is forecast. Placement of Lvl 2 reflects where the models and their ensembles suggest the highest likelihood of storms or of storm tracks with high values of vertical vorticity and where favorable conditions will exist for intense low-level rotation. Even outside of Lvl 2, within lvl 1 area and near its borders, storms will be capable of tornadoes or severe wind gusts.
... SW to central France in the night hours ...
The cold front will reach the region with redevelopment of storms forecast along it towards Thursday morning. While forecast profiles show 15 - 20 m/s of 0-6 km bulk shear, only marginal MUCAPE is forecast by the models. With the storms only ramping up around 06 UTC and severe weather threat being quite low, will not introduce a Lvl 1, though the severe weather risk, both in terms of heavy rainfall and hail are forecast to increase further towards Thursday noon.
... N Greece through N Macedonia, Serbia, Bosnia into Romania, Hungary, Slovakia and SE Poland ...
Modestly moist airmass with mixing ratios of 10 to 12 g/kg is forecast ahead of a decaying cold front. A convergence zone will set up between moister airmass with northerly flow and easterly/southeasterly flow with drier airmass with steeper lapse rates. The convergence zone will be pronounced especially over S Serbia. A local overlap of steeper lapse rates and moist airmass will yield MLCAPE values up to 1500 J/kg, decreasing N. Outside of the convergence zone, initiation will depend mostly on the orography of Romania and Slovakia. Vertical wind shear will reach around 15 m/s in the 0-6 km layer. Forecast profiles and hodographs suggest (marginally) large hail and heavy rainfall as the main risks across the area. Very large hail and severe wind gusts are possible across the southern fringes of Lvl 1 and within Lvl 2 with higher LCLs and CAPE values. The best shear and the highest coverage of storms are expected over Serbia, where supercells would be most likely with eventual upscale growth. Across Hungary, coverage of storms is highly uncertain and may depend on the storms spreading from Serbia or Bosnia further N/NE, especially in the late evening and night hours.
... NE Turkey through Caucasus into S Russia ...
Scattered to widespread storms are forecast ahead of a pronounced mid to upper tropospheric short-wave, initiated primarily by the local orography. Forecast profiles reveal moderate MLCAPE values with largest buoyancy in the hail growth zone, 0-6 km bulk shear around 15 m/s and rather low LCLs, increasing towards Turkey. Expect a combined risk of large hail with heavy rainfall owing to the numerous rounds of storms possible. Storms will spread NE during the day, eventually affecting also S Russia.
... 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.
