Forecast Update
Valid: Tue 21 Aug 2012 14:00 to Wed 22 Aug 2012 06:00 UTC
Issued: Tue 21 Aug 2012 14:20
Forecaster: GROENEMEIJER

A level 2 was issued for parts of eastern France and SW Germany mainly for large hail and severe winds, and to a lesser extent for excessive precipitation.

A level 2 was issued for Western, central and eastern parts of Germany for severe winds, tornadoes and large hail.

A level 1 was issued surrounding the level 2, including central and E France, much of Germany, the Alpine countries, SW Poland, the Czech Republic and parts of Slovakia and Hungary for some large hail, excessive precipitation and local wind.

A level 1 for the NE Romania and Moldova is issued primarily for severe wind gusts and to a lesser extent for large hail.

DISCUSSION

Northwestern, northern and northeastern Germany...

A surface warm front has developed stretching from a mesoscale low over North-rhine Westfalia to the Berlin area. Near the front, rather high low-level shear is observed per Bergen and Essen soundings, the latter of which also shows weakly capped modest CAPE.
As large-scale upward vertical motion increases upon approach of the through, convective storms are expected to develop by early evening, and should do so in a strongly sheared environment. It is well possible that a few supercells will travel eastward along the frontal zone. Given the strong low-level shear they will have a chance of producing tornadoes, in addition to a threat of strong wind and hail.

Central and NE France, Switzerland, SW Germany...

Abundant (~ 2000 J/kg) CAPE has developed across NE and east-Central France, given surface dew points that have remained well in excess of 20 C despite solar heating. Storms are expected to develop during the evening. Given moderate to strong shear, these are probably well-organized supercells with a threat of large hail, and severe winds. The focus of the convective activity will probably move into Germany. The convection may then change to a bowing system with damaging winds as its main threat.

NE Romania, Moldova...

A bowing convective system is travelling along the NW-SE oriented baroclinic zone in NE Romania. The overall environment does not look particularly severe, given modest CAPE and wind shear, but a couple of severe wind gusts and some marginalyl severe hail may well occur.