Storm Forecast
Valid: Wed 19 May 2021 06:00 to Thu 20 May 2021 06:00 UTC
Issued: Tue 18 May 2021 20:38
Forecaster: PUCIK

A level 1 was issued across parts of Balkans mainly for severe wind gusts and marginally large hail.

A level 1 was issued across western Russia / eastern Belarus / eastern Ukraine mainly for heavy rainfall, with severe wind gust and hail threat increasing towards the east and north.

A level 1 was issued across Finland mainly for large hail and to the lesser degree for severe wind gusts.

SYNOPSIS

Deep and extensive low continues to cover much of central Europe with a strong jet at its base. Several short-waves surround the low. The first one will cross the Aegean Sea and western Balkans. Another one will rotate from the Black Sea towards southern Russia and the third one will move from northwestern Russia towards Finland. Closer to the surface, a frontal boundary runs across the southern Mediterranean through Balkans, Turkey, curving northward/northeastward from Caucasus towards southern Finland. A pronounced frontal wave is forecast to develop over northwestern Russia and proceed across Finland during the forecast period.

Isolated to scattered storms are forecast across much of western and central Europe under marginal CAPE and/or weak shear conditions. Here, severe threat will be rather marginal. Marginal CAPE, but strong vertical wind shear combined with decent synoptic-scale lift is forecast across Bosnia and surrounding area and also Caucasus. Over these areas, few supercells may form and produce large hail and/or severe wind gusts.

More extensive severe weather threat is forecast over parts of Russia and Finland. This area requires more detailed discussion.

DISCUSSION

... Western Ukraine, Eastern Belarus into northwestern Russia (Lvl 1 with >50% lightning probability) ...

Skinny CAPE profiles together with high RH throughout the mid-troposphere are forecast across the area, suggesting heavy rain threat. Moderate 0-6 km bulk shear, mostly between 10 to 15 m/s suggests multicellular storm organisation. Locally, higher values of shear may result in better organised storms and enhanced threat of either large hail or severe wind gusts. The highest severe weather threat is forecast across northwestern edge of Russia, where a short-wave trough will eject towards Finland and where 0-6 km bulk shear values will be the highest.

... Russia (Level 1, but < 50% probability of lightning) ...


This area will be displaced from the surface frontal boundary, which combined with higher values of CIN and higher LFC will make the convective initiation more uncertain. ECMWF and ICON break out isolated storms at best over the area. GFS is more aggresive, but this is likely due to the dewpoint overestimation. The area will reside underneath a plume of steep lapse rates. Forecast soundings and hodographs reveal Inverted-V profiles and 0-3 km bulk shear exceeding 15 m/s, suggesting a threat of severe wind gusts. Large hail may also occur with stronger updrafts. While coverage of storms remains highly uncertain, will keep a rather large Lvl 1 as any storm that forms in the environment will have high chance of producing severe weather, especially severe wind gusts.

... Finland ...

Considerable uncertainty remains in this forecast scenario as a short-wave trough, together with a frontal wave cross the region. Ahead of the short-wave, a zone of steep mid-tropospheric lapse rates will be advected over southeastern / eastern Finland. Warm sector will be characterized by rather dry boundary layer, very steep lapse rates and 0-3 km bulk shear exceeding 20 m/s. Given successfull convective initiation, this would be a very dangerous setup for severe convective wind gusts. That said, CIN values / LFC height will remain high in the warm sector and the synoptic-scale lift will likely stay confined to the cool side of the frontal boundary, making convective initiation unlikely or uncertain. The cool side of boundary will also involve strongly sheared environment, but will only support elevated storms, which will not utilize the strong shear present in the bottom 1 - 2 km of troposphere. Nevertheless, severe weather threat will be non-zero even with the elevated storms. All NWP simulates widespread convective rainfall in the wake of the boundary, yielding high chances of lightning in this zone. Lvl 2 was considered for parts of Finland for the risk of more widespread severe wind gusts, but was discarded due to the uncertainty in the surface-based development during the day. Nevertheless, the area needs close monitoring for any signs of initiation in the zone with SBCAPE > 0 J/kg.