Mesoscale Discussion
Valid: Thu 04 Sep 2025 11:00 to Thu 04 Sep 2025 14:00 UTC
Issued: Thu 04 Sep 2025 11:08
Forecaster: TUSCHY

This Mesoscale Discussion (MD) was issued to highlight an evolving severe risk through the afternoon into the evening. The MD's validity does not match the timing of the severe risk (roughly 13Z to 18/19Z).

Clearing in the MD area is well underway with 2m dewpoints now sneaking into the mid tens. The mid-tropospheric flow turns more southerly betimes as the main trough approaches, so a N-ward fanning alpine EML (e.g. sounding Innsbruck 03Z) overspreading this BL moisture is forecast to create a confined area with MUCAPE up to /in excess of 2000 J/kg. Already impressive (numerical) shear profiles continue to improve especially with regard to SRH with ID2 offering locally in excess of 25kt 0-2 km SR inflow.

During the afternoon, initiating and rapidly maturing convection stays semi-discrete for some time as it crosses the Swiss MD NE. This activity could produce swaths of large hail, strong/severe downbursts and heavy rain as it crosses into the German MD area. Dependant on storm-internal processes, we could either see ongoing semi-discrete cells or upscale growing bowing segments in case of an evolving/maturing RIJ event. Both is possible and especially the latter risk could cause the convection to stay worth a level 2 for some time, before lowering CAPE and CIN issues should start a gradual weakening trend. Especially higher elevations could see extreme gusts in case a more elevated RIJ evolves. Colliding convection and (in case of a bowing segment) book-end vortices could also produce swaths of excessive rain with lots of low/mid tropopsheric moisture being present.
An isolated tornado risk is possible, both with deepening mesocyclones in a low LCL background or embedded in LEWP structures, which take profit of strong SR inflow.

In the eastern part of the German MD area, a few supercells are possible with similar hazards. The best parameter setup stays confined to the Alps, so a weakening trend occurs as this activity spreads N/NE.