Severe storms expected in Italy, Croatia, Bosnia and Herzegovina, Montenegro and Albania
Valid: Tue 05 Nov 2019 06:00 to Wed 06 Nov 2019 06:00 UTC
Issued: Mon 04 Nov 2019 23:21
- A level 2 has been issued for Italy for excessive precipitation, severe wind gusts and to a lesser extent, tornadoes.
- A level 2 has been issued for, Croatia, Bosnia and Herzegovina, Montenegro and Albania for excessive precipitation, severe wind gusts and to a lesser extent, tornadoes.
- A level 1 surrounds the level 2 areas for the same threats but with less coverage extent.
A positively-tilted trough over western Europe associated with an advection of cold maritime air masses results in the development of a deep cyclone with a center over the English Channel as of Tuesday 05/11 06z. The south propagation of this trough over the western Mediterranean creates a strong south-westerly flow over Central Mediterranean increasing the threat of severe weather events in Italy and western Balkans. Limited instability is found in the latest numerical output guidance but strong kinematics and high amounts of moisture over the Mediterranean may lead to severe weather events listed in the following discussion. Finally, limited convective activity is expected in the Gulf of Biscay, SW France, and SE Aegean Sea but thermodynamics will not support any severe threat apart from a local small hail/graupel event.
Italy, Croatia, Bosnia and Herzegovina, Montenegro and Albania
The approaching trough from the western Mediterranean is about to provide a large-scale lift to unstable air masses in the Central Mediterranean, even though mid-level lapse rates do not look promising to develop high CAPE values, especially over land.
Low-topped storms should start forming in the morning of Tuesday west of Italy and will propagate fast east embedded to a strong southwesterly flow and with weak lightning activity given the limited vertical extent of CAPE, placed mostly below 500 hPa.
In the northern parts of Italy, the vertically integrated water is forecast to be less than to the southern parts of the country, but the low and mid-level flow will be stronger and can be translated to the surface within the storms. An increased threat for severe wind gusts is forecast along the west coasts of Italy.
Moreover, orographic lifting will result in persistent rainfall which may lead to flash-floods, even though most of accumulated precipitation will be non-convective. In addition, the strong low-level flow increases the 0-1km wind shear and it locally overlaps with some hundreds of MLCAPE and high SREH, thus a few tornadoes cannot be ruled out.
The same analysis can be repeated for western Balkans as the same environmental ingredients are expected with a slight time shift, even with a stronger low/mid-level jet streak. An increased thread for flash-floods is expected and local severe wind gusts, as well as a few tornadic events. Forecasting hodographs do not seem impressive in terms of low-level storm-relative helicity but local orographic features may enhance the low-level flow and lead to tornadogenesis.