Storm Forecast
Valid: Tue 06 Sep 2016 06:00 to Wed 07 Sep 2016 06:00 UTC
Issued: Mon 05 Sep 2016 21:09
Forecaster: DAFIS
A level 2 was issued for parts of Greece, Albania and SE Italy mainly for excessive rainfall and severe wind gusts.
A level 2 was issued for parts of Italy - Sardenia, Corsica and N Tunisia mainly for large hail and severe wind gusts.
A level 1 surrounds the level 2 areas for the same threats but it was also issued for tornado threat at the coasts of the aforementioned countries.
SYNOPSIS
A cut-off low makes its way from Central Europe towards Central Mediterranean basin during Tuesday, while a ridge is forming in West Europe. This low pressure system attains high vorticity values, with a jet streak at its western flank over Italy where scattered but strong thunderstorms are forecast. Very moist and unstable air masses will be advected towards Greece where excessive rainfall events are expected to be numerous. Furthermore, a short-wave trough will cross the NW Iberian Peninsula but CI is questionable due to a strong low level cap. Two more short-wave troughs are visible in the upper level maps, east and west of Scandinavia but apart from strong dynamics (high PV values), instability is weak. Rather stable conditions at the rest parts of the continent will suppress any convective phenomena.
DISCUSSION
.... Greece, Albania and SE Italy ....
During the early morning of Tuesday we expect a cold front on the surface to move from N Adriatic Sea towards Greece, where a first round of organized thunderstorm activity will take place, possibly in a form of a squall line. As the front will propagate eastward, locally strong convergence lines in the southern and eastern parts of Greece after 18z, will pose a serious threat for flash floods as a plume of unstable air masses with mixing ratios up to 15 g/kg build MLCAPE values up to 1000 J/kg. Moreover, GFS predicts 200-300 mē/sē SREH0-3km over this area and a vorticity maxima will be found over the eastern mainland of Greece during the night, increasing the probability of supercell development. High resolution models (WRF, BOLAM, etc.) forecast a strong BL convergence zone in and around the Gulf of Taranto, in S Italy where DLS reaches 20 m/s and PW exceeds 35 mm. Even though DLS is weak in the rest parts of level 1, small hail is not excluded, but severe wind gusts and heavy downpours will be the main threats. In the morning of Wednesday, LLS is increasing over Ionian Sea, overlapping with some hundreds of SBCAPE and waterspouts or/and tornadoes are expected.
.... Italy - Sardinia, Corsica and N Tunisia ....
For these areas, abundant synoptic lift, the upper-level jet configuration, the strong divergence atop and the overlap of 25-30 m/s DLS over unstable air masses suggest serious threats for any storm that will form. GFS does not produce abundant CAPE in level 2 area, but signals of 1000-1200 J/kg with weak cap, steep mid-level lapse rates and strong DLS cannot rule out large to very large hail events and severe wind gusts, with less confidence for N Italy as CAPE is expected to be in the range of 400 - 800 J/kg.
