2019 Summer Discussion (Northern Hemisphere)

Any storm that will form inside the level-2 area will be able to become quickly a supercell due to the strongly sheared and helical environment. IFS forecasts more than 1500 J/kg MLCAPE overlapping with 15-20 m/s DLS and comparable 0-3km bulk shear, with more than 150-200 m2/s2 SREH0-3km. This environment will be ideal for thunderstorms to produce large to very large hail and severe wind gusts. Moreover, strong low-level shear and veering winds create looped forecasting hodographs with nearly 100 m2/s2 SREH0-1km and adding the low LCLs in all available NWP models, tornadoes cannot be ruled out, but this will depend on the convective mode. AROME model (12z run) shows a QLCS in N France, but also some discrete supercells which may produce tornadoes.

... rest of France, Belgium, Luxemburg, the Netherlands and Germany ....

Very steep mid-level lapse rates create fat CAPE profiles and NWP models forecast excessive CAPE, mostly over France, with values exceeding locally 2000 J/kg. Storms will be able to produce large hail, more than 2-3 cm in diameter and severe wind gusts. In particular, vertical thermodynamic profiles over Germany, S Belgium and E-NE France show mid-level dry slots and high LCLs, increasing the probability of severe convective gusts at the surface, as strong evaporation cooling of downdrafts may accelarate them to high speeds.