Storm Forecast
Valid: Fri 22 Sep 2023 06:00 to Sat 23 Sep 2023 06:00 UTC
Issued: Thu 21 Sep 2023 23:14
Forecaster: PUCIK/KUZMENKO
A level 2 was issued across Corsica, Italy, W Slovenia and W Croatia mainly for heavy rainfall, tornadoes, damaging wind gusts and large hail.
A level 1 was issued across SW France mainly for severe wind gusts and tornadoes.
A level 1 was issued across Sardegna mainly for heavy rainfall and severe wind gusts.
A level 1 was issued across E Austria, NW Croatia, W Hungary, W Slovakia and NE Czechia mainly for severe wind gusts.
A level 1 was issued across Bulgaria mainly for severe wind gusts.
SYNOPSIS
A deep trough moves across the western half of Europe with strong flow surrounding it, reaching locally over 60 m/s at 300 hPa level. The strongest upper tropospheric forcing is forecast ahead of the base of the trough, which will move towards Italy during the forecast period. Closer to the surface, a cold front will stretch from the W Mediterranean through the Alps into Czechia, W Poland and Sweden at the beginning of the forecast period. Poor mid-tropospheric lapse rates will limit the thunderstorm and severe weather potential across northern half of the front, while high coverage of severe weather is forecast across parts of Italy.
DISCUSSION
... SW France ...
Scattered storms will form in strong lower tropospheric flow with 0-1 km bulk shear reaching up to around 15 m/s. Isolated severe wind gusts or tornadoes will be possible in more intense storms. The threat will be the highest in the early morning hours of Friday, when the strongest low level shear is forecast.
... Corsica to Italy, Slovenia and Croatia ...
A complicated forecast scenario will unfold over the area. Early into the forecast period, storms will already exist over or close to Corsica, over Gulf of Genoa and S Alps. Already these storms may be severe, posing combined risks of heavy rainfall due to saturated profiles and severe wind gusts and/or tornadoes given substantial shear in the bottom 1 and 3 km.
During the day, storms will spread further E and S. It is possible that numerous supercells will form during multiple times across N Italy. Continuous warm-air advection combined with the orographic lift is shown by the models. Forecast soundings and hodographs point to the risk of heavy rainfall and tornadoes owing to moist lower troposphere and 0-1 km bulk shear around 10 m/s. Hail risk will increase towards the late afternoon over NW Italy, where more abundant buoyancy in the hail growth zone is simulated.
Numerous storms, including supercells and well-organised convective systems, are forecast to develop and move across central Italy and the Adriatic Sea and its coastlines in the afternoon to late evening and night hours. Forecast soundings and hodographs suggest that all hazards are possible. Substantial CAPE will combine with 0-6 km bulk shear over 25 m/s and SRH exceeding 150 m2/s2 in the 0-1 km locally. The predominant type of severe weather may depend on the convective mode with supercells producing tornadoes and large hail while linear systems capable of severe wind gusts and heavy rainfall. The (very) large hail threat will increase towards S and higher CAPE values. A strong tornado is possible within a Lvl 2, especially along the W Italy and Croatian coastline, where some models depict very strong low-level shear. Severe weather threat is forecast to persist well overnight as the storms spread S along the cold front.
... E Austria, W Hungary, SW Slovakia, NE Czechia ...
While models do not agree on the presence of storms over the region in the afternoon to evening hours, strong low-level shear combined with Inverted V profiles is agreed on. The storms that do form in this environment will pose a risk of severe wind gusts.
... Sweden ...
Strong low-level shear is forecast along the cold front. In this environment,isolated to scattered, but weakly electrified, storms will form. A lvl 1 has been considered for the area, but it is questionable whether the storms will manage to become surface based.
... Romania and Bulgaria ...
Forecast soundings and hodographs reveal potentially severe situation with Inverted-V profiles and decent 0-3 km bulk shear reaching 10 - 15 m/s, especially over Bulgaria. However, majority of models don't show any convective precipitation over the area, the exception being ECMWF. A questionable Lvl 1 is introduced over parts of Bulgaria, where the strongest 0-3 km shear is simulated and where the forecast profiles suggest the highest likelihood of initiation.
