Storm Forecast
Valid: Tue 01 May 2018 06:00 to Wed 02 May 2018 06:00 UTC
Issued: Mon 30 Apr 2018 22:32
Forecaster: DAFIS

A level 2 was issued for parts of Poland, Lithuania, and Belarus for large or very large hail, severe wind gusts, excessive precipitation, and tornadoes.

A level 1 was issued for parts of Poland, Lithuania, Latvia, Russia, Belarus, and Ukraine mainly for large hail, severe wind gusts, excessive precipitation, and tornadoes.

A level 1 was issued for E Croatia, SW Hungary, N Serbia and N Bosnia and Herzegovina mainly for large hail, severe wind gusts, tornadoes and excessive precipitation.

SYNOPSIS

A long-wave trough in W Europe has brought unseasonably cold air masses and torrential rainfall and snowfall in NW France. Two vorticity maxima will be found tomorrow, one over the Iberian Peninsula and another one over N Germany – Denmark. East Europe is under the influence of warm and moist air masses where a slow-moving front will be the steering mechanism of convective activity on Tuesday 1 May. Steep lase rates and unstable air masses can also be found in the Balkans, Asia Minor, Middle East and S-E Spain. Finally, NWP models forecast the development of a low-pressure system in Algeria which will propagate NE in C Mediterranean on Wednesday.

.... Poland, Lithuania, Latvia, Russia, Belarus, and Ukraine ....

The level-2 areas will reside below steep lapse rates and a strongly sheared environment, able to produce all kinds of severe weather. At the warm sector of a slowly moving front, we expect widespread CI before noon as storms will cluster in the afternoon in an MCS or supercell. Forecast hodographs suggest that a squall line can form, able to produce severe wind gusts and tornadoes. The highest probability of tornadogenesis is in C-E Belarus where LLS and SREH0-1km are maximized. More discrete storm cells will be capable of producing large to very large hail, since 15-20 m/s DLS and up to 2000 J/kg MLCAPE will overlap during the maximum diurnal heating. Moreover, dry mid-levels and deep PBLs increase the chance for severe wind gusts and large hail. Convective activity will continue during the night of Tuesday and early morning of Wednesday.

A level 1 surrounds the level 2 area for the same threats but with lower probability. The main threat in level-1 areas will be excessive precipitation from training convection (Poland, Belarus) and slowly-moving storms in Russia.

.... E Croatia, SW Hungary, N Serbia and N Bosnia and Herzegovina ....

Diurnal heating will drive convective phenomena in the Balkans and the level-1 area shows where we expect the most severe weather events. High-resolution models forecast up to 1500 J/kg MLCAPE in E Croatia and 10-15 m/s DLS. Veering wind profiles in forecast hodographs support the idea of strong MCSs or supercells which will be able to produce large hail, severe wind gusts, and tornadoes. The storms will slowly propagate N to Hungary late in the afternoon and flash floods may occur. Storms may survive in Hungary until Wednesday morning but elevated convection will decrease the severe weather threats.