Severe storms in Europe: A level 2 issued for corridor from France to Belarus and Ukraine
Valid: Mon 01 Jul 2019 06:00 to Tue 02 Jul 2019 06:00 UTC
Issued: Sun 30 Jun 2019 23:54
A level 2 was issued for a corridor from parts of E France to SW Belarus and NW Ukraine mainly for severe wind gusts, large to very large hail and excessive precipitation.
A level 1 was issued for a corridor from S France to S Belarus and N Ukraine mainly for large hail, excessive precipitation and severe wind gusts.
A level 1 was issued for W Russia mainly for large hail, severe wind gusts, excessive precipitation and tornadoes.
Thick geopotential with a warm and highly unstable tropical airmass persists over majority of S and E parts of Europe Broad low is placed over Scandinavia and induces passage of a shallow long-wave through parts of CNTRL and E Europe during a forecast period. At 1200 UTC a boundary with a cold front and very high theta-e horizontal gradient will be stretching from CNTRL France through CNTRL Germany, CNTRL Poland up to N Belarus. Thunderstorms are expected to fire-up in the warm sector ahead of that boundary. An outbreak of severe to extremely severe thunderstorms is possible in the corridor from E France to S Belarus where an overlap with a mid-tropospheric jet will be the most prominent.
Ahead of the approaching cold front, low-level convergence zone provide rich BL moisture with MIXR up to 13-15 g/kg. Along with steepening mid-level lapse rates to more than 7 K/km, a solid corridor of 2000-3000 J/kg ML CAPE develops in the warm sector.
Selected NWP model outputs like GFS indicate values exceeding even 4000 J/kg in parts of S Germany, Czech Republic, Belarus, NW Ukraine and W Russia around 1500 UTC. Eastwardly traveling shallow long-wave provide a narrow (~100km) overlap of mid-tropospheric jet with aforementioned unstable airmass. The most prominent overlap concerns S Germany, Czech Republic, S Poland, S Belarus and W Russia with 15-20 m/s (locally >20 m/s) 0-6km shear. Low-level jet resulting in 15-20 m/s 0-3km shear will also support severe thunderstorms in Czech Republic, S Poland, S Belarus and W Russia.
Storms developing in aforementioned areas may be evolving into supercells and be capable of producing large to very large hail and heavy rain. However, a rather straight hodographs should provide rapid clustering and increase potential for damaging winds within bowing segments of convective lines. Less prominent overlap of shear and instability will be available over surrounding areas (parts of France, Alps, N Italy) where a threat for a local severe thunderstorms will still exist within slowly moving multicell clusters / pulse thunderstorms with a potential for producing severe wind gusts, large hail and excessive precipitation (PW > 35mm)
Storms developing in W Russia in the environment of clockwise-curved hodographs (SRH > 300-400 m2/s2) will have a good potential for evolving into supercells. Enhanced LLS (> 10 m/s) and LCLs below 750m will create a chances for tornadoes. Based on the most recent NWP output, current understanding is that first elevated storms may fire-up in the early morning hours over parts of W and CNTRL Poland and move eastward. Due to enhanced environmental wind shear these storms may be capable of producing severe wind gusts, large hail and heavy rainfall.
In the afternoon hours cap should start breaking and surface-based CI is expected to take place over S Germany, S France, Switzerland and Czech Republic. In the environment of 10-15 m/s (locally up to 20 m/s) these storms may be capable of producing large hail, damaging winds (especially S Germany and W Czech Republic) and heavy rain. Large hail is also possible within Alpine area where a local enhancement in vertical wind shear may take place and result in some isolated supercell event.
In the late evening hours a large MCS developing on the border of Czech Republic and Poland should move into SE Poland and later during nighttime to S Belarus and N Ukraine. The main threat with this system should be severe wind and heavy rainfall. Although environment will be supportive for well-organized storms over W Russia, a lack of prominent synoptic-scale lift induces CI to be uncertain for surface-based storms (which is also confirmed in a disagreement of different NWP model scenarios). Therefore, level 2 is not issued for this area.