VALID FOR 02 / 03 / 04-11-2018
A large trough is located over the N Atlantic while a large part of Europe is under the influence of extensive ridge centered over the eastern Europe. To the south, two upper lows are located: one is the SE Mediterranean and one, the most robust one, in the southern Mediterranean. An associated surface cyclone ejects from northern Algeria towards N Tunisia and Sicily tonight, before turning towards Sardinia on Saturday.
HIGH and MDT RISK have been issued for SW Sicily across the Strait of Sicily, Lampedusa and extreme NE Tunisia with threat for severe storms capable of producing large hail, severe winds, tornadoes and especially extreme amounts of rainfall. An environment with good overlap of moderately strong instability (1000-1500 J/kg) and strong deep-layer shear (50-70 knots) will be conductive for an explosive development of organized storms tonight into tomorrow morning. Given the amount low-level instability and good helicity, strong tornadoes are possible as well. Locally, 150-200 mm or even more rainfall in a 18-24 hour period should lead to dangerous flash floods, resulting from both orographic and convective rainfall. A large MCS cluster with training storm cells is possible overnight into the early morning on Saturday.
MDT RISK has been issued for eastern Sardinia island into western Tyrrhenian sea with threat for excessive rainfall and locally 100+ mm per 24-hour period. A combination of persisting ESE moist low-level winds and shallow convection, heavy and excessive rainfall is likely through the day tomorrow.
ENH RISK has been issued for surrounding areas of HIGH / MDT RISK areas including eastern Sardinia and SE Corsica islands, parts of south-central Italy (Calabria region), Sicily across Gozo (Malta) into NE Tunisia where threat for mainly excessive rainfall is expected. However, given the at least marginal to even moderate MLCAPE along the NE-wards moving cold front, storms are also expected across the Tyrrhenian sea towards the southern Apennines mountain range and lead to torrential rainfall and enhanced flash floods threat locally.
SLGT RISK has been issued for surrounding areas of HIGH / MDT and ENH RISK areas where some isolated threat for severe storms exists. The main threat will be excessive rainfall.