Storm Forecast
Valid: Sat 03 Oct 2015 06:00 to Sun 04 Oct 2015 06:00 UTC
Issued: Sat 03 Oct 2015 00:51
Forecaster: DAFIS
A level 2 was issued for South France mainly for excessive rain, large hail, severe wind gusts and to a lesser extent for tornadoes.
A level 1 surrounds level 2 area for the same threats but with less spatial coverage.
SYNOPSIS
A shortwave trough over the Bay of Biscay shifts eastward during Saturday and crosses France. At the surface a cold front will cross Cevennes-Vivarais area where convergence zones between the Massif Central and the Alpes will propagate some MCS able to produce severe weather phenomena. At the other parts of the continent high geopotentials and stable conditions will lead to fair weather, except from the Mediterranean Sea where CAPE is present, CIN is absent and several storm cells are expected. Moreover, a cyclonic vortex in the Black Sea and another one in NW Russia dissipate until Sunday morning.
DISCUSSION
.... France and NW Italy ....
The aforementioned shortwave trough with a vorticity max over southern parts of France during Saturday results in abundant convective initiation even from the early morning hours. Unstable Mediterranean air masses (BL mixing ratio 10-13 g/kg) are advected onshore at the Gulf of Lion area and we forecast severe weather in the Cevennes-Vivarais area where MLCAPE of about 1000 J/kg overlaps with strong DLS of 20-25m/s. Two or more MCS are forecast within this area and/or probably a supercell given the high SREH values of 0-3km exceeding the 400 mē/sē. High resolution models predict the formation of a QLCS in the level 2 area, so a bow echo is also possible with sereve wind gusts being the main threat and tornadoes of lesser concern, as strong LLS is juxtaposed with CAPE. Some slow storm cells will be able to produce excessive rainfall and large hail. In the level 1 area we expect excessive rain and large hail but also some waterspouts on Sunday morning at the Gulf of Genoa because of the LLS and the presence of CAPE. Furthermore, waterspouts are also forecast for the Adriatic Sea coastline.
