Storm Forecast
Valid: Tue 18 May 2021 06:00 to Wed 19 May 2021 06:00 UTC
Issued: Mon 17 May 2021 22:12
Forecaster: DAFIS
A level 2 was issued for parts of W Russia mainly for large hail and severe convective wind gusts.
A level 1 was issued for a large part of eastern Europe for large hail, excessive precipitation, and severe convective wind gusts.
A level 1 was issued for SE Bulgaria, NE Greece and N Turkey mainly for large hail and excessive convective precipitation.
A level 1 was issued for Central Europe mainly for excessive convective precipitation and large hail.
SYNOPSIS
An unseasonably cold air mass has invaded western and central Europe, and its interaction with the subtropical, much warmer air mass over the Mediterranean, results in a wavy strong jet stream. The strong zonal flow is interrupted in eastern Europe where a meridional WAA brings unstable air masses north, all the way north to Scandinavia. Another mid-level jet in W Russia will be the main reason for DMC events during this outlook.
DISCUSSION
.... Eastern Europe ....
A very moist and warm, and thus unstable air mass flows north over eastern Europe, resulting in severe weather events where CI occurs. The confluence that will result in between a high-pressure system in Russia and a low-pressure system over Ukraine is expected to create a convergence zone just where the level-2 area is placed. Along with the maximum diurnal heating in the early afternoon, CI is more than certain. Apart from the lifting mechanisms, there is a consensus among the available NWP models that the steep mid-level lapse rates and the high theta-e low-level air mass will build locally more than 2000 J/Kg MLCAPE. At the same time, DLS is calculated to exceed 15-20 m/s and high values of CAPESHEAR increase the threat for severe DMC. Rather straight forecast hodographs limit the probability of isolated supercell development, but this scenario cannot be excluded. Any isolated supercell will be able to produce large or very large hail. The storms that will organize into MCSs will be able to produce severe convective wind gusts and excessive precipitation. The storm motion vectors will point north and elevated storms may reach Finland and the Arctic Cycle during the night of Tue 18/05 where excessive precipitation will be the only threat.
More to the south, in Belarus and Ukraine, the main threat will be excessive convective precipitation from diurnally-driven convection. DLS is much weaker over this region and storms will be slow-moving and highly efficient in producing rainfall as the forecast saturated vertical profiles show. Storms should completely stop during the night.
.... Bulgaria, Greece and Turkey ....
Placed under a mid-level jet streak, storms that will manage to form during the traverse of a short-wave trough will be able to produce large hail. First, CI will have better chances in the mountainous S Bulgaria and storms will propagate fast east, towards Greece and Turkey where also unstable air masses lie. In the afternoon and evening on Tue 18/05, only Turkey is expected to experience thunderstorm activity, but the organization and lifetime of these storms will depend on the mid-level ventilation due to the very strong mid-level flow (15-20 m/s) and whether they will become elevated.
.... Central Europe ....
Quite similar conditions with the Balkans are expected also in Central Europe on Tue 18/05. A high-shear / low-CAPE configuration complicates the forecast, but a level 1 area is placed to show the areas with the higher chances of severe DMC. Storms that will develop into this strongly sheared environment will be able to produce hail and severe wind gusts. Hail may not exceed in size the 2cm, but in large quantities can also pose a threat. In the evening, storm activity will completely stop.
