Storm Forecast
Valid: Wed 26 Jul 2023 06:00 to Thu 27 Jul 2023 06:00 UTC
Issued: Tue 25 Jul 2023 23:07
Forecaster: GROENEMEIJER
A level 2 was issued across a part of Russia for tornadoes, which may be strong, and to a lesser extent for extreme rainfall, large hail, and severe wind gusts.
A level 2 was issued across the central Balkans for large hail and severe wind gusts, and to a lesser extent for heavy rainfall.
A level 1 was issued across an area surrounding these level 2 areas, with tornadoes and hail more important across Russia and Ukraine, and the risk of hail and wind stronger across the Balkans.
A level 1 was issued across northeast Italy and western Slovenia, and across eastern Italy, both for large hail and to a lesser extent for severe wind gusts.
SYNOPSIS
A mid-/upper-level trough initially across eastern Germany and Czechia is elongating, reaching an axis from eastern Poland to northern Greece on Thursday morning. At the surface, a cold front is moving southeastward across the Balkans and Central Mediterranean with some severe storms forming ahead of it and isolated marginally severe storms across the northern Adriatic. Further downstream, several baroclinic waves have developed across the front, which stretches roughly from Northern Romania to the Moscow region. Ahead of the low-level troughs at the tip of these waves, i.e. across the level 2 regions Ukraine and Russia, considerable helical flow indicates the risk for a few tornadoes near the front in spite of somewhat meagre instability.
DISCUSSION
Central Balkans...
Ahead of the southeastward moving cold front, considerable instability of about 1000 - 2000 J/kg of MLCAPE is expected to build in a rather strongly sheared environment with 20-25 m/s of 0-6 km bulk shear. Promoted by some quasigeostrophic forcing for upward motion ahead of the mid/upper-level trough axis, some storms are expected to form across the level 2 area centered over Serbia and its surroundings. A few supercells with large, and locally very large hail are expected. Some severe wind gusts may also develop with such storms and with storms that cluster and organize linearly.
Moldova and Ukraine...
Along the front that should move little in these areas, a wave is developing associated with pressure falls across far southwestern Ukraine. A narrow zone of high low-level storm-relative helicity is expected on the cool side of the front, where some 1000 J/kg of instability should be present. However, the numerical models suggest that this instability stays slightly elevated during the day. As a result, not more than a level 1 is warranted. The area should, however, be monitored for a higher risk of tornadoes that could develop if surface-based instability would evolve.
Russian level 2 area and surroundings...
A surface cyclone tracks northwastward from far eastern Belarus with an associated frontal wave. In contrast to the area across Ukraine, considerable surface-based instability is expected in this region within the wave's warm sector with MLCAPE in the 1000 - 2000 J/kg range. In combination with strong storm-relative helicity with values of 100-200 m2/s2 in the 0-1 km layer, this indicates a serious tornado potential with the storms that are expected to become surface-based during the morning as the low moves northeastward. Given the strength of the shear, some of the tornadoes may be strong.
Northeast-Italy...
A few storm may develop in the afternoon in a postfrontal environment still boasting considerable CAPE and moderate deep-layer shear. Some multicells and low-topped supercells with large hail are likely to develop.
East-Italy...
Models devierge quite a bit about the magnitude of the risk across this area, which is highly sensitive to the amount of low-level moisture that is advected inland, as this modulates the available CAPE. Taking a moderate scenario, it seems likely that 1000-1500 J/kg of MLCAPE and 20 m/s of deep-layer bulk shear are the parameters a few isolated storms will have to work with. This suggests that some large hail, and, possibly, some severe winds might occur locally.
