Above is the current lightning map for Europe today; this is the first mass CB/Thunderstorm event of 2017.
These occur regularly during the Euro-summer, and operations in NL, Germany, Switzerland, and Austria get heavily impacted.
Eurocontrol says: CB activity with local Thunderstorm activity forecast over Austria, Germany and Switzerland. Several en route and aerodrome arrival regulations have been applied.
EDDF, EDDM, EDDS, Paris TMA, LOWW, LSGG and LSZH. Moderate to High delays can be expected.