Mesoscale Discussion
Valid: Thu 03 Aug 2017 15:00 to Thu 03 Aug 2017 19:00 UTC
Issued: Thu 03 Aug 2017 15:16
Forecaster: PISTOTNIK

...S Germany, N Switzerland, Austria ...

Strong insolation towards the southeast and a dense band of clouds and rain to the northwest have enhanced the temperature gradient across southern Germany and Austria - e.g., 24°C in Würzburg, 31°C in Munich and 37°C in Vienna at 14 UTC. The cooler but very moist airmass cuts beneath the hot and dry air in several surges of NW-erly winds.
A few storms have already formed and organized into supercells in SW Germany. As the capping inversion is further eroded by large-scale lift ahead of a short-wave trough, scattered additional storms may initiate anytime (or to root down from Altocumulus clouds). Orographic features like the Swiss and Swabian Jura, the Black Forest or the Northern Alps (where the first surge of NW-erly wind has arrived and is pumping plenty of moisture into upslope flows) help in this process.
2m dewpoints mostly between 17 and 20°C and fairly steep lapse rates create CAPE between 500 and 1500 J/kg under strong 0-3 km shear (15-20 m/s), confirmed by the 12 UTC Stuttgart and Munich soundings. Storms that forms can organize into supercells and pose a risk of large hail (>5 cm not ruled out locally) and downbursts. Directional wind shear is limited, but in case a supercell propagates off the hodograph, a tornado is possible.
The rather flow-parallel orientation of the leading convergence line enhance the risk of flash floods in Austria, especially in case of training storms or upscale growth into a large cluster in the evening.