Storm Forecast Valid: Wed 07 May 2014 06:00 to Thu 08 May 2014 06:00 UTC Issued: Tue 06 May 2014 21:20 Forecaster: PUCIK
A level 1 was issued for parts of France, Italy, Germany, Czech Republic and Poland mainly for marginally large hail and severe wind gusts.
A broad trough at mid-troposphere is forecast to move from British Isles / N France towards east with seasonably strong flow, reaching 20 - 30 m/s at 500 hPa on its forward and rear flanks. Another trough will lift over Russia towards the northeast while a lingerning pool of low geopotentials will remain over SE Europe. Closer to the surface, a frontal system will shift across Western and Central Europe during the day. The primary area of concern will be an area behind the weak cold front, where modest low-level moisture (dewpoint temperatures around 10 °C) along with synoptic-scale lift will result in marginal latent instability.
... Central France ... NW Italy ... NW Czech Republic ... E Germany ... NW Poland
Only modest instability is resolved by numerical models with GFS being the most optimistic one and ECMWF simulating only small "patches" of CAPE. On the flanks of the progressing trough, 20 to 30 m/s flow at 500 hPa is forecast, yielding high values of DLS (above 20 m/s in the 0-6 km layer). Shear profiles should be mostly unidirectional, without significant SREH values and with relatively weak flow at 850 / 700 hPa. No strong forcing is forecast with only weak PVA and ill-defined frontal system progressing across the region. Isolated to scattered thunderstorms will form in the early afternoon towards evening. Given the strong DLS, some well organised multicells (or even supercells) could form with attendant threats of marginally large hail / severe wind gusts. A Lvl 1 is issued for the areas with the highest expected CAPE / shear overlap, despite the uncertainities regarding the real degree of instability.