Valid: Tue 05 May 2015 06:00 to Wed 06 May 2015 06:00 UTC
Issued: Mon 04 May 2015 22:39
A level 1 was issued for SE Germany, NW Austria, Bohemia, W Poland mainly for large hail, severe wind gusts and to the lesser degree for tornadoes.
A level 1 was issued for N Germany mainly for severe wind gusts and tornadoes.
Main synoptic-scale feature will be a deep trough over the Atlantic as steering southwesterly flow ovespreads much of W and Central Europe. With tropical airmass spreading northward, a ridge will also amplify from the Mediterranean through Balkans into Poland. Short-wave will rotate around trough, from BENELUX towards Denmark and S Scandinavia. Closer to the surface, frontal system of seasonably deep low pressure system will affect Central Europe. Cold front will progress eastward during the day, reaching W Poland, Bohemia and Austria till Wednesday morning.
Most of the DMC activity will be confined to the warm sector of the frontal system, ahead or along the cold front.
... SE Germany, NW Austria, Bohemia, NE and N Germany, W Poland ...
As strong SW-ly flow overspreads warm sector with 500 hPa windspeeds above 20 m/s, wind profiles will favour well-organised DMC, including supercells. DLS is forecast to reach values 20 - 30 m/s over the whole region. Over northern half of the area, LLS over 10 m/s is simulated as well, given 850 hPa flow reaching 15 - 20 m/s. Models indicate that a plume of steep lapse rates will contribute to hundreds J/kg of MLCAPE, perhaps locally even higher (especially close to the Alpine foreland). However, there is disagreement between the models regarding the degree of destabilisation. Furtheremore, it is possible that cloud cover may inhibit surface heating significantly.
With short-wave travelling northwest of the risk area, forcing will remain in the form of low-level convergence zones ahead or along the surface cold front. There is also significant disagreement in models regarding initiation and coverage of DMC in particular areas.
As such, situation is supportive of severe thunderstorms, primarily capable of large hail and/or severe wind gusts. Threat of severe wind gusts or tornadoes will be elevated over the northern part of area, where stronger low-level flow is forecast. If isolated supercell manages to track along the N Alpine foreland, steeper lapse rates and enhanced SREH may allow for an isolated report of very large hail. Due to the numerous uncertainities, Lvl 1 was kept for all mentioned areas.