Mesoscale Discussion
Valid: Wed 04 Jun 2025 13:00 to Wed 04 Jun 2025 15:00 UTC
Issued: Wed 04 Jun 2025 12:43
Forecaster: TUSCHY

A Mesoscale Discussion was issued to update the evolving severe risk. Please keep in mind that the MD's validity does not match the expected time for organized DMC activity.

Morning/elevated convection cleared the area of interest N. As the lead impulse is about to enter Switzerland from the SW, a temporarily backed mid-level flow regime now assists in stronger subsidence along/N of the Alps with drying/clearing and BL warming. 2m temperatures now rise into the low to mid twenties. A 1037Z AMDAR from Munic captures the evolving loaded gun pattern very well with MUCAPE now in excess of 1500 J/kg with steadily increasing DLS (12Z now exceeds 1800 J/kg MUCAPE with 24 m/s DLS). Cap is a bit lower based than forecast with a cool 900 hPa layer, but otherwise a steady weakening trend is expected with ongoing (temporal) diabatic heating. Forecast BL stratification seems to be well handeled as dewpoints remain (mostly) in the mid/upper tens with local peaks up to 20C along the dryline itself.

We still see mixed signals in NWP guidance regarding CI with some models taking organized convection from Switzerland into the MD area, with others showing discrete CI in the open warm sector along the periphery of the dryline and next to a weak LL vortex over far SE Bavaria.
Right now we can't decline any of those scenarios. Thus the dryline needs to be monitored closely for isolated CI during the mid to late afternoon hours as cap weakens to allow BL convergence to become strong enough for evolving updrafts (especially where the dryline and the diffuse vortex intersect). In case we see this scenario unfolding, explosive CI is forecast and rapidly organizing mesocyclones will be capable of producing hail and gust events up to the extreme level (see Day 1 forecast). Of note is the constant CI now shown by RUC to the SW of Munic, which would place this major city in the mentioned risk area.

Around the same time we expect the Swiss activity to spread into the MD from the SW and the stage seems to be still set for growing clusters with long swaths of damaging hail and severe gusts. Some models weakened the gust signatures and this could be the lingering issue regarding how much cap remains left during the late afternoon into the evening hours. 12Z Kuemmersbruck has still -90 J/kg CIN in place but modification to late afternoon values of latest CAMs in the BL reveals only slim capping should be left. Hence we continue to highlight a chance for long-tracked severe bowing segments and embedded supercell, which track NE trough the MD area into Czechia during the night especially with 0-3 km shear values in te 15-20 m/s range.