Storm Forecast
Valid: Sun 08 Sep 2024 06:00 to Mon 09 Sep 2024 06:00 UTC
Issued: Sat 07 Sep 2024 21:17
Forecaster: PUCIK
A level 2 was issued across NW and central Italy mainly for heavy rainfall, (very) large hail, severe wind gusts and tornadoes.
A level 2 was issued across NE Italy, W Slovenia and Istria mainly for very heavy rainfall and to the lesser extent for tornadoes.
A level 2 was issued across Algeria mainly for damaging wind gusts and large hail.
A level 1 was issued from the Balearic towards Tyrrhenian Sea, including Corsica and Sardegna mainly for heavy rainfall, severe wind gusts and large hail.
A level 1 was issued across E France and S Germany mainly for marginally large hail and severe wind gusts.
A level 1 was issued from central to N Germany mainly for heavy rainfall.
A level 1 was issued across Turkey mainly for large hail and heavy rainfall.
DISCUSSION
... N and central Italy ...
A classic autumn severe weather situation is forecast across the region. Moderate to high MLCAPE is forecast to be present over the area basically during the whole forecast period before the frontal passage. Some storms will be present over Liguria and Tuscany already in the morning hours. These will pose risks of very heavy rainfall and large hail. Further increase in the storm coverage is anticipated in the evening to overnight hours with the passage of a front and approach of a sharp trough at the upper troposphere. While there is a possibility of a long-lasting rainstorm in the morning and early afternoon hours, evening to overnight storms will quickly shift E/SE in conjuction with the fast translation of the initiation mechanism.
Severe weather threat will increase towards the evening hours. Model simulate considerable increase in the hodograph length and curvature. 0-6 km bulk shear will exceed 25 m/s with 0-1 km bulk shear approach locally 15 m/s with 0-1 km SRH over 200 m2/s2. Dominant severe threat will depend on the convective mode and the thermodynamic profile. If surface-based supercells form, there will be a risk of tornadoes, including strong ones. However, this is questionable with some models simulating profiles conducive only to elevated storms. High-resolution models show a window for surface-based supercells forming in strong low-level shear especially over the Apenines in the late afternoon hours. Numerous high updraft helicity tracks are simulated. Elevated supercells would still be capable of at least (very) large hail and severe wind gusts. While hail threat may be diminished by CAPE getting skinnier towards the upper troposphere, significant effective shear above the inflow base could well compensate for that. Given strong windfield in the lower troposphere, any forward propagating MCS will be capable of damaging wind gusts. Repetitive passage of storms over an area will result in significant risk of heavy rainfall given low LCLs and moist profiles. The highest risk of heavy rainfall will be over Tuscany, where areas may receive rainfall from both the morning and late afternoon/evening storms. Combined risks of all mentioned threats easily warrant a Lvl 2 due to the expected high coverage of severe weather.
... NE Adriatic ...
A strong WAA regime is forecast to develop across the area during the overnight hours. Due to the cyclogenesis across N Italy, 850 hPa windspeed may ramp up to 25 m/s, yielding powerful low-level jet and pronounced curved hodographs with significant low-level shear. Inland, elevated storms are expected, riding the low-level jet. Efficient rainfall processes are forecast with CAPE mostly confined to the warm part of the cloud and low LCLs. Repetitive passage of cells will be likely and local models suggest rainfall amounts possibly exceeding 200 mm at some locations. Heavy rainfall will be the dominant threat. Tornadoes are not ruled out if surface-based storms will develop. This threat will be pronounced especially over the S flank of the area.
... N Africa ...
A subtle frontal boundary is forecast to initiate scattered to widespread storms as it crosses the region. Over the past days, substantial low-level moisture has advected quite far inland with multiple rounds of (severe) storms. Saturday will be no exception. The main threat will be severe wind gusts with fast-moving storms developing in unidirectional hodograph with 0-6 km bulk shear between 15 and 25 m/s. The strongest shear is forecast towards the S with ICON-EU and ECMWF painting a serious setup with 0-6/0-3 km bulk shear approaching 25 m/s and forecast hodographs suggestive of environment conducive to both intense supercells and bow-echoes. Such scenario warrants a Lvl 2 for multiple swaths of severe wind gusts and large hail.
... SE France ...
Scattered storms are forecast to develop along the cold front. CAPE and shear overlap will allow for a couple of stronger multi or supercells with main threats being heavy rainfall and large hail.
... Germany ...
Models indicate storms developing along and behind the cold front. The highest threat of severe weather will exist over S Germany, especially near the Alps, where models indicate several pre-frontal supercells initiated by the orography. Marginally large hail and severe wind gust threat will accompany the strongest storms. High-resolution models consistently indicate this scenario. Further N, storms will develop mostly behind the front, in an area of elevated CAPE. Repetitive passage of cells training over the front may result in a local heavy rainfall event.
... E Turkey ...
Scattered storms will be initiated by the orography on the forward flank of a stationary mid to upper tropospheric trough. While low-level moisture will be modest, lapse rates exceeding 7 K/km will allow for MLCAPE values around 1000 J/kg. With much of CAPE being confined to the temperatures below 0 deg C and shear allowing for at least transient supercells, expect large hail to be the dominant threat.
