Storm Forecast
Valid: Wed 14 Oct 2015 06:00 to Thu 15 Oct 2015 06:00 UTC
Issued: Tue 13 Oct 2015 22:14
Forecaster: PUCIK

A level 2 was issued for parts of Central Italy mainly for excessive precipitation, tornadoes and to the lesser degree for large hail.

A level 1 was issued for Italy, the Eastern Adriatics coastline mainly for excessive precipitation and to the lesser degree for large hail and tornadoes.

A level 1 was issued for parts of Northern Africa mainly for severe wind gusts and large hail.

SYNOPSIS

Main macrosynoptic feature will be a large and deep cyclonic vortex centered near BENELUX and NW Germany. Its trough will stretch all the way towards Algeria with southwesterly prevailing flow over much of the central Mediterranean. In this flow, a plume of steeper lapse rates will be advected from N Africa over the moist boundary layer of the sea, contributing to moderate to high CAPE values, especially over the Tyrrhenian Sea and near Tunisia. At the same time, a surface cyclogenesis is forecast over N Italy with a tongue of abundant low-level moisture impinging on the coastlines of Central Italy and the Adriatics. Abundant DMC activity is forecast here. Rest of Europe will be under relatively stable and/or dry conditions.

DISCUSSION

... Tyrrhenian Sea towards the Adriatics ...

Surface observations reveal dewpoints between 15 - 20 deg C over the region. Dewpoints are forecast to increase especially over the Adriatic Sea during the day thanks to the southerly component of the low-level flow. A belt of CAPE is forecast to develop as the southwesterly flow advects plume of steeper lapse rates over the area with values mostly between 500 - 1500 J/kg with higher values possible over the Tyrrhenian Sea. At the same time, strong SW-ly flow will contribute to DLS reaching 15 - 25 m/s over a wide area. LLS will exceed 10 m/s locally, especially close to the coastlines. Conditions thus seem to be prime for well-organised DMC.

DMC is forecast to be organised especially in the large clusters, possibly one or more MCS as the cells are repeatedly initiated along the coastlines or convergence zones. One prominent convergence zone is simulated over Tyrrhenian Sea near Central Italy, where it could linger for numerous hours. Thanks to the very moist boundary layer and high chance of cell training as inititiation is focused on one spot, excessive rainfall is the primary threat. In case that supercells manage to form, large hail and tornadoes may occur as well, the latter especially along the convergence zones. A Lvl 2 is introduced for the region with the highest threat of flash flooding during the period.

... N Africa ...

As the NW-ly flow advects moister airmass inland, in combination with steep lapse rates, CAPE build-up on the order of few hundreds J/kg is forecast. Thanks to the presence of rather steep lapse rates and strong DLS, well organised cells (including supercells) will be capable of isolated large hail and severe wind gusts.