Mesoscale Discussion
Valid: Thu 22 Jun 2017 14:00 to Thu 22 Jun 2017 17:00 UTC
Issued: Thu 22 Jun 2017 14:08
Forecaster: PISTOTNIK

... E Germany into W Czech Republic ...

The long-lived bow echo which crossed N and E Germany in the past six hours produced a long swath of severe wind gusts, while an embedded supercell at its southwestern flank was responsible for hailstones up to 4 cm in size. The most active part of the storm is located near Leipzig now (14z), and its high intensity and bowing shape still suggest a pronounced wind risk. However, dewpoints decrease along its further path, hence a weakening trend is expected to start soon. Low dewpoints between 8 and 12°C in most of the Czech Republic do not support CAPE any more (see the 12z Prague and Prostejov soundings).
The storm system has pushed a strong outflow to the SW, which may initiate new convection anytime. Under high CAPE (around 2000 J/kg) and moderate vertical wind shear (10-15 m/s across the lowest 3 km), a quick storm organization with a risk of large hail and severe downbursts can be expected.
The area in central Germany where this outflow boundary cuts into the path of a second round of organized storms coming from the west (please refer to the other Mesoscale Discussion covering W Germany) needs special monitoring for particularly explosive storms. A tornado is not ruled out in this region, where low-level shear is enhanced and moisture may be pooled.

... S Austria ...

The 12z Vienna sounding shows an overlap of robust CAPE (1500 J/kg) and enhanced 0-3 km shear (15 m/s) under the fringe of a NW-erly mid-level jet downstream of the subtropic ridge. Mid-level flow is weaker on the southern side of the Alps, but southerly upvalley and upslope winds stil maintain vertical wind shear of the same magnitude. CAPE is regionally even higher, as evaporation after two days of intense afternoon storms have pushed 2m dewpoints up to 20°C.
Due to a capping inversion and a lack of synoptic-scale lift, only isolated storms are expected in the next few hours, but they turn multi- and supercellular with a primary risk of large hail.

Conditions are similarly good in N Italy but the stronger cap is expected to suppress storm formation.