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Storm Forecast
Valid: Thu 04 Sep 2025 06:00 to Fri 05 Sep 2025 06:00 UTC
Issued: Tue 02 Sep 2025 22:56
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.
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.