DISCUSSION
An outbreak of severe thunderstorms is forecast over parts of Germany, Switzerland, SE-France and N-Italy with large hail, tornadoes and severe wind gusts
This set-up, although quite supportive for widespread severe thunderstorms, still features major uncertainties. The main uncertainties arise over SE-Germany and W-Germany, described in the respective paragraphs.
... SE-France, N-Italy, Switzerland and W-Austria ...
This area is the one with the highest degree of certainty that widespread severe will occur. As a sharp upper trough draws near from the west during the forecast and overspreads a hot and very moist airmass, that features surface dewpoints in the lower twenties (at 19 UTC, yesterday). In addition, lapse rates at mid-levels steepen due to an approaching EML, so MLCAPE of 1000 - 2000 J/kg is a reasonable forecast for the regions south of the Alps with up to 1000 J/kg over E-/S-Switzerland. South of the Alps, DLS increases to 25m/s with roughly 250 m^2/s^2 SRH-3, so strong mid-level updraft rotation is forecast with those thunderstorms. Supercells with large hail are forecast and hail in excess of 5cm is possible, next to organized downdrafts with severe wind gusts, given well mixed subcloud layer mainly over the southern/eastern parts of the level-2. During the afternoon hours, a depression at the surface is in progress and intensifies during the following hours, which enhances shear at low-levels. A sharp decrease of LCL heights from the south to the north is expected due to drier/warmer air to the south. For now, especially the southern parts of the level-2 have the highest tornado threat, which is also in line with the local WRF3, showing a sharp moisture gradient with impressive shear and EHI values of 2-3. An isolated strong tornado can't be ruled out. The activity spreads eastwards during the night with a continuos severe risk.
