Mesoscale Discussion
Valid: Thu 22 May 2014 17:00 to Thu 22 May 2014 20:00 UTC
Issued: Thu 22 May 2014 17:09
Forecaster: PISTOTNIK

... W Germany ...

Convective activity has recently increased along a North-South-oriented convergence zone over Western Germany. Between 15 and 16 UTC, strong pressure rises and gusts up to 21 m/s occurred at the affected stations. Obviously the storms' individual cold pools have fused into a continuous front that will make a swift NE-ward progress. Strong unidirectional 0-3 km wind shear (20-25 m/s shown by the 12 UTC soundings from Idar-Oberstein and Essen) and evaporative cooling in the deeply mixed, dry prefrontal air (24-28°C surface temperatures, 8-13°C dewpoint) support a threat of severe wind gusts. Though a lack of CAPE may limit a better storm organization, a few (partly embedded) supercells are possible in case discrete updrafts can form over pockets of augmented moisture. This applies in particular if initiation occurs well ahead of the ongoing system, e.g. presently near Kiel.
Near the Southern rim of the highlighted area, two probable supercells have been active so far. The first one formed over the Black Forest mountains at 15 UTC and tracked NNE-ward until it decayed recently, while the second one just popped up at its outflow boundary near Stuttgart. Large hail and severe wind gusts can be expected in its NNE-ward track.

... S Germany ...

Strong pressure rise will push the outflow boundary to the East into Bavaria, where it encounters even drier air. With Foehn subsidence, dewpoints in the Northern Alpine foreland have dropped from 12-15°C to values as low as 2°C in recent hours, with temperatures near 30°C. The Munich 12 UTC sounding confirms that initiation and sustenance of convective updrafts is very unlikely in such a dry environment. The very high CAPE values up to 2000 J/kg and beyond, which were uniformly shown by NWP models with persistent upslope flow along the Alpine rim, can therefore be discarded. A dry wind shift line with strong to isolated severe Westerly wind gusts will pass in the next few hours.