Storm Forecast
Valid: Thu 05 Aug 2021 06:00 to Fri 06 Aug 2021 06:00 UTC
Issued: Thu 05 Aug 2021 00:08
Forecaster: GATZEN

A level 2 was issued across SE Poland to S Belarus for heavy rain and tornadoes.

A level 2 was issued for E Slovakia to W and central Ukraine for severe wind gusts and to a lesser extent tornadoes and large hail.

A level 2 was issued for NE Hungary to S Ukraine and N and E Romania for severe wind gusts and large hail.

A level 2 was issued for S Croatia, S Bosnia and Herzegovina and Montenegro for large or very large hail, tornadoes and severe wind gusts.

A level 1 was issued for the Adriatic, N and central Balkans for large or very large hail and severe wind gusts.

A level 1 was issued for W Russia for severe wind gusts.

A level 1 was issued for E Netherlands, central Germany, W Czech Republic for heavy rain.

A level 1 was issued for E Turkey, Caucasus for severe wind gusts.

SYNOPSIS

Low geopotential across NW Europe expands towards the east with a mid-level vortex moving towards the British Isles. An impressive Atlantic mid-level jet is directed towards the west Mediterranean and curves around the base of an intense short-wave trough progressing across the Adriatic into the Ukraine today.

At lower levels, a plume of hot and well-mixed air is pushed into SE Europe ahead of the short-wave trough, while a cold front progresses across the Adriatic and Balkans. A trough extends across central Europe where rather moist air is present.

DISCUSSION

Adriatic, Balkans, Ukraine and surroundings

Ahead of the approaching short-wave trough, strong QG forcing due to DCVA and WAA is expected to spread NE. A cold front enters the area form the west while a warm front intensifies across the Ukraine.

Convective activity is expected by latest models along the cold front across the Adriatic Sea and especially along the eastern shores, where upslope advection of a moist and unstable air mass is expected. Due to very strong vertical wind shear below the jet axis, with 30 m/s DLS, well-organized storms are forecast.

Due to strong forcing along the front, an MCS is likely to spread from N to south, with embedded supercells possible. Main threat if this MCS will be high winds and large hail, and also very large hail is not ruled out. Additionally, due to strong low-level shear, tornadoes are not ruled out.

Dry conditions to the east will limit severe potential. Additionally, as QG forcing spreads NE, CAA and frontolysis is expected over the S Adriatic Sea, and the MCS is forecast to become weaker during noon.

Farther east, a rather dry and well-mixed air mass will be affected by the cold front. Due to dry profiles and strong vertical wind shear, convection initiation is limited, and storm mode is expected to be isolated. Storms that manage to form will rapidly organize posing a threat of high winds and large or very large hail. Convective activity is forecast to spread from W to NE rather quickly as cold air advection sets in during the afternoon.

Better low-level moisture is expected from E Romania towards the Ukraine and E Slovakia. This moisture will also partly overlap with steep mid-level lapse rates advected ahead of the approaching trough. MLCAPE in the range of 1000 J/kg is expected in the afternoon and evening.

Some storms are forecast along the warm air advection regime in the afternoon across SE Poland, N Ukraine into W Russia. Limited CAPE and shear will also limit severe potential at first, with some large hail and severe wind gusts the main threat. Heavy rain is most likely in the western parts where moist profiles and skinny CAPE are present together with strong QG forcing.

Farther south, the cold front will support widespread initiation in the afternoon. Due to strong vertical wind shear, supercells are expected that move east, capable of producing large or very large hail and severe wind gusts. Tornadoes are not ruled out although the LCL is expected to be rather high and low-level moisture is limited. Tornado potential increases close to the warm front across NW Ukraine with long and favorably curved low-level hodographs and also lower cloud bases.

Late in the period, storms are forecast to merge into one of two MCSs along the cold front, spreading ENE into Belarus and W Russia. Severe threat gradually shifts to severe wind gusts that may go on until the morning across W Russia.

Netherlands, Germany, W Czech Republic

In a rather cool but moist air mass, slow-moving thunderstorms are expected to develop along a broad convergence zone and topography-induced convergence. These storms are capable of producing locally heavy rain in the noon and afternoon before decaying after sunset.

E Turkey, Caucasus

Warm air advection affects this area in the range of a well-mixed, hot air mass. Mountain-valley circulations will support some diurnally-driven thunderstorms with a potential of severe wind gusts due to inverted-v profiles.