Storm Forecast
Valid: Mon 07 Aug 2023 06:00 to Tue 08 Aug 2023 06:00 UTC
Issued: Sun 06 Aug 2023 20:51
Forecaster: PUCIK/KUZMENKO
A level 2 was issued across Lithuania, Latvia, S Estonia, Belarus, N Ukraine and W Russia for damaging wind gusts, large hail, tornadoes and heavy rainfall.
A level 2 was issued across Sweden for heavy rainfall, tornadoes, some of which may be strong, and severe wind gusts.
A level 1 was issued across Norway for heavy rainfall and to the lesser degree for tornadoes and severe wind gusts.
A level 1 was issued across Finland mainly for severe wind gusts.
A level 1 was issued across Carpathians mainly for heavy rainfall.
A level 1 was issued across Croatia, Bosnia, Montenegro, Serbia mainly for severe wind gusts and large hail.
SYNOPSIS
At mid to upper troposphere, a deep trough will be located across central Europe with strong flow, exceeding 30 m/s at 500 hPa, surrounding its southern and eastern flank.Two short-wave troughs will rotate around the main trough. The first one will move across the Adriatic Sea towards Serbia. The second one will move from Romania towards Ukraine, Belarus and the Baltic countries. Close to the surface, an unseasonably deep low will be located over the Baltic Sea, its warm front moving from Sweden to Norway and its cold front moving from Belarus and Ukraine towards Russia and the Baltic countries. Within the warm sector, very warm and humid airmass is forecast with 850 hPa temperature up to 20 deg C and mixing ratios above 12 g/kg.
DISCUSSION
... Ukraine, Belarus, Lithuania, Latvia, Estonia, W Russia ...
Widespread thunderstorms are forecast along the advancing cold front ahead of the short-wave trough. Strong linear forcing will likely result in a fast upscale growth. Storms will form in a strong lower tropospheric flow, reaching around 20 m/s at 850 hPa and 25 m/s at 700 hPa level. This will yield strong shear both in 0-1 and 0-3 km layer with hodographs mostly straight in shape. Current thinking is that a mix of supercells and bow-echoes will form along the cold front moving N. Primary risks will be severe to even extremely severe wind gusts, followed by large hail and tornadoes. Convection allowing model has simulated numerous supercells with high values of updraft helicity in the area. Heavy rain risk will increase with increasing convective coverage towards the evening hours as storms may repetitively move over some areas as they train along the front. Limiting factors of the situation will be twofold. First, the cold front moving N may undercut the supercells and/or bow-echoes moving with more W component of motion. Second, significant dry layer in the mid-troposphere outside of the frontal boundary in the warm sector will reduce the strength of updrafts or chances that the storms can be maintained there.
... Finland ...
Presence of significant dry layer in the mid-troposphere significantly reduces the chances of convective initiation in the warm sector. Storms are simulated especially along the warm front lifting N. A Lvl 1 is introduced for the risk of damaging wind along the warm front given strong low-level shear. South of the warm front, probability of convective initiation will be close to 0.
... Sweden ...
Elevated storms capable of very heavy rainfall will move across the area as the warm front moves towards Norway. Another round of storms is forecast in the afternoon hours, but some questions remain concerning the exact location. Storms can be initiated either by orography or by a local boundary between warm airmass inland and cooler airmass from the sea. Long and curved hodographs are forecast with around 15 m/s of 0-1 km bulk shear and locally around 200 m2/s2 of SRH in the 0-500 m layer. If surface-based supercells manage to form in this environment, there will be a risk of strong tornadoes. Models are not in agreement concerning the lapse rates in the boundary layer and also the exact location of convective initiation in the afternoon hours. Nevertheless, Lvl 2 seems to be warranted due to the combined risk of tornadoes, severe wind gusts and heavy rainfall throughout the whole day.
... Carpathians ...
A small lvl 1 is introduced for a risk of heavy convective rainfall with slow moving storms forming in moist profiles.
... Croatia, Bosnia, Serbia ...
While models agree on the approach of the trough and strong deep-layer shear (> 25 m/s in 0-6 km bulk shear) across the region, the availability of CAPE is questionable. Nevertheless, Lvl 1 seems to be well warranted as supercells may form capable of large hail and/or severe wind gusts.
