Mesoscale Discussion
Valid: Tue 10 Jun 2014 15:00 to Tue 10 Jun 2014 18:00 UTC
Issued: Tue 10 Jun 2014 16:04
Forecaster: PISTOTNIK

Explosive storm development is taking place where the capping inversion over Central Europe is broken!

... E France, Switzerland, SW Germany ...

12z soundings (Payerne, Stuttgart) and latest surface observations confirm moderate CAPE (~1000 J/kg) and moderate deep-layer shear (~15 m/s). Numerous well-organized storms, including several splitting storms and probable right-moving supercells, have initiated over orographic features like the Massif Central, the Vosges, Swiss Jura and Black Forest, and recently also along the Swiss Northern Alpine rim. Large hail and severe wind gusts are the main threat. The latter is fostered by deep subcloud layers in the very hot air mass with dewpoint spreads regionally in excess of 20K. The risk of flash floods gradually declines as storms lose their orographic anchoring.
Activity will move northeastward or propagate along outflow boundaries. In general, it is expected to keep its present level of intensity or even grow upscale.

... W Germany ...

A pronounced convergence line has crystallized which slowly moves eastward. To its West, gradually cooler and drier air is advected, and storms over Belgium and the Netherlands have decayed. In the range of the convergence line over Western Germany, CAPE on the order of 1000 to 2000 J/kg is still available under roughly 15 m/s unidirectional deep-layer shear according to latest observations. First storms have just initiated and may turn into multi- and supercells with a risk of large hail and severe wind gusts. Upscale growth may start towards the end of the forecast period. In case a forward-propagating MCS manages to travel along the convergence line, the risk of damaging winds would strongly rise!

... E Germany into SW Poland ...

This morning's large storm cluster has pushed an outflow boundary to the South and Southwest, associated with a strong capping inversion which kept the sky cloudless. In the wake of this boundary, 5 m/s Northeasterly surface winds are present and dewpoints have risen to values between 17 and 21°C beneath the cap. 12z Meiningen and Wroclaw soundings indicate CAPE on the order of 1200 J/kg and some surface observations from the surroundings suggest even up to 2000 J/kg. Deep-layer shear is increased to 20 m/s by the strongly backed surface winds. To sum it up, conditions for organized convection seems better than predicted.
However, it remains questionable if the cap can be broken. So far, explosive initiation of backbuilding storms has been confined to the leading edge of the outflow in Eastern Germany. Any storm that forms can turn into a supercell with a risk of large hail, heavy rain and severe wind gusts.