Storm Forecast
Valid: Sat 05 Aug 2017 06:00 to Sun 06 Aug 2017 06:00 UTC
Issued: Sat 05 Aug 2017 01:10
Forecaster: TASZAREK

A level 1 was issued for a corridor extending from NE Spain up to Czech Republic mainly for the large hail, severe wind gusts, and excessive precipitation.

A level 1 was issued for E Slovakia, SW Ukraine and SE Poland mainly for the large hail, severe wind gusts, and excessive precipitation.

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

A level 1 was issued for W Turkey mainly for the large hail, severe wind gusts, and excessive precipitation.

SYNOPSIS and DISCUSSION

On Saturday Europe is divided by a jet stream on a cool polar airmass at the north and warm and moist tropical airmass at the south. Broad low covers N Baltic Sea and moves eastward. The quasi-stationary frontal boundary extends from France, through CNTRL Germany, Poland, Belarus and parts of W Russia. A shortwave passes by a western side of this boundary (France, Germany, Alps) in the late afternoon and night-time hours. The highest thermodynamic instability along with rich moist BL is located on the warm side of the boundary, with peak values over S France, Alpine area, Ukraine and W Russia. The same areas are covered (thanks to the jet stream) with an enhanced DLS extending from 15 m/s over Ukraine, up to 20-25 m/s over Alps and W Russia. Given PVA over France and Germany, and LL convergence within Poland/Slovakia/Ukraine border, storm should initiate in the afternoon hours according to current NWP scenarios. In the environment of ~ 1500 J/kg ML CAPE and aforementioned vertical wind shear, storms should be able to evolve into multicell clusters and supercells capable of producing large hail, downburst type severe wind gusts and excessive rain, especially given moist profiles (35-400mm PW) in the tropical airmass. The best veering wind profiles are expected over S France, NE Spain and Ukraine becoming even better in the late afternoon. Storms on the E and S flank of the low over Baltic, should evolve before noon and fade in the late evening. The best chances for the organized severe convection within this feature is located on its eastern flank where instability area line up with the position of jet stream. Although ML CAPE is expected to be rather low (~ 600-800 J/kg), a support of the high DLS (25-30 m/s) and strong 700 hPa flow (> 20 m/s) may help to organise convection into supercells and linear multicell clusters with a potential of producing severe wind. Storms evolving over Turkey will remain in the weakly sheared environment and moderate instability. However, few large hail incidents are not ruled out given steep lapse rates and higher terrain elevation. Slowly moving storms may also cause heavy rain and local flash flooding, especially in the mountain area. CI is the most likely in the afternoon hours along with intensifying diurnal heating. Storms over this area should fade in the late evening.