Mesoscale Discussion
Valid: Tue 01 Aug 2017 15:00 to Tue 01 Aug 2017 18:00 UTC
Issued: Tue 01 Aug 2017 15:01
Forecaster: PISTOTNIK

... Switzerland, SW Germany ...

Latest surface observations indicate two boundaries with converging winds which will likely become a focus of convective initiation in the next few hours:

(1) A pronounced dryline has formed along the northern Alpine rim, which separates very moist NE-erly upvalley flow in the forelands from hot and dry S-erly Foehn winds in the Alpine valleys. Latest 14z observations show temperature and dewpoint values of e.g. 28/22°C in Ricken versus 34/10°C in Glarus (E Switzerland), 31/21°C in Feldkirch versus 36/8°C in Bludenz (W Austria), or 29/20°C in Kaufbeuren versus 33/7°C in Reutte (bordering area between Germany and Austria). So far the upvalley flow has been dominant and has "piled" plenty of low-level moisture against the Alps especially in Switzerland, where stations even at an altitude of 800-1000 meters are recording dewpoints around 20°C. This deep moisture likely supports CAPE on the order of 2000 to 3000 J/kg on the moist side of the dryline.
(2) The second boundary is formed by cooler NW-erly outflow winds, which are spreading southward in the wake of an area of clouds, rain and elevated thunderstorms that has moved from E France into W Germany. At 14 UTC, this boundary ran roughly parallel to the dryline and was located about 300 kilometers north of it.

The southern and northern rim of the highlighted area on the map correspond to the 14 UTC positions of the dryline and the outflow boundary, respectively. First storms have recently initiated along both boundaries and are quickly organizing in this environment of high CAPE and ~20 m/s deep-layer shear.
It appears likely that the further increasing mid-level winds will start pushing the dryline northward, while the outflow boundary is proceeding southward, so they may eventually merge and lay out an axis of converging winds and maximized moisture which favourably aligns with the expected storm tracks from SW to NE. It is not ruled out that a large, long-lived storm system with a high-end risk of severe to extreme hail and wind events may materialize and affect N Switzerland and SW Germany in the next few hours.