Storm Forecast
Valid: Thu 21 Jun 2018 06:00 to Fri 22 Jun 2018 06:00 UTC
Issued: Thu 21 Jun 2018 09:40
Forecaster: TASZAREK

A level 2 was issued for parts of SE Poland, W Belarus, W Ukraine, parts of Czech Republic and Slovakia mainly for severe wind gusts, large hail, tornadoes and excessive precipitation.

A level 1 was issued for a corridor stretching from W Hungary to Latvia mainly for severe wind gusts, large hail, tornadoes and excessive precipitation.

A level 1 was issued for W parts of Iberian Peninsula mainly for large hail, severe wind gusts and excessive precipitation.

DISCUSSION & SYNOPSIS

A broad long-wave with a very cold air mass (0°C at 850 hPa) and strong jet surrounding the wave travels eastwardly through British Isles, Scandinavia and N parts of CNTRL Europe. Ridge is located over E Ukraine. Almost stationary cut-off low is placed over waters W of Portugal. Rich boundary layer's moisture (MIXR > 10 g/kg) stretches in the corridor from NW Iberian Peninsula, through S France, Alps, Balkan Peninsula and up to the warm sector ahead of the approaching long-wave (Baltic Countries, E Poland, Belarus, Ukraine). Enhanced boundary layer's moisture covers also Italy and Turkey. Within the support of a strong diurnal heating, local convergence zones and orographical lift thunderstorm development is possible in the all aforementioned areas as the healthy CAPE will exceed 800-1000 J/kg. Thunderstorms developing over W parts of Iberian Peninsula will have the support of a strong lapse rates (> 7.5 K/km) and moderate shear (> 15 m/s). Multicells and supercells capable of producing large hail, severe wind gusts and heavy rain are a possible scenario for this area. Heavy rain may support local flash flooding events as some of the thunderstorms may remain stationary. High PW with CAPE exceeding 1000-1500 J/kg and locally even 2000-2500 J/kg in the corridor from W Balkan Peninsula to Baltic Countries will promote thunderstorms with a potential for heavy rain and downburst-type severe wind gusts. The best chances for organized severe thunderstorms are within E flank of the approaching long-wave (Poland, Baltic Countries, Czech Republic) where a prominent forcing and favorable vertical profile of wind (> 10 m/s LLS, > 15 m/s MLS and > 150 m2/s SRH) may promote supercells with a potential for large hail, severe wind gust and tornadoes, especially in the late afternoon hours after 16-18 UTC. However, probability for the tornadoes will be limited by the enhanced LCL and dew-point depressions. In such kinematic wind field, development of a linear system with a potential for damaging wind gusts cannot be ruled out. Thunderstorm activity will shift to Belarus and W Ukraine during the night and maintain potential for severe wind gusts. Majority of thunderstorm activity should develop in the afternoon hours along with enhancing diurnal heating. Thunderstorms with the highest severe weather potential over E parts of Poland are expected to develop in the late afternoon hours. A night-time lightning activity will maintain in the corridor stretching from Serbia to Belarus.