Storm Forecast
Valid: Sat 21 Nov 2015 06:00 to Sun 22 Nov 2015 06:00 UTC
Issued: Fri 20 Nov 2015 20:56
Forecaster: DAFIS
A level 1 was issued for Italy, Corsica, Slovenia, Croatia, Bosnia and Herzegovina, Montenegro and Albania mainly for excessive rainfall, severe wind gusts and tornadoes.
SYNOPSIS
The frontal set up over Europe is very complex but the main features of Saturday's weather will be the outbreak of polar air and the cyclogenesis in North Italy. A large frontal zone which runs all the way from Ukraine to the Gulf of Biscay will be disorganized by the Alps and we expect the formation of a low pressure system at the lee side of the mountain range.
As cold air enters the Mediterranean Sea, steep lapse rates are formed over the mild sea surface and models forecast CAPE values of up to 400 J/kg.
DISCUSSION
.... Italy, Corsica, Slovenia, Croatia, Bosnia and Herzegovina, Montenegro and Albania ....
Global NWP models are consistent with the location of a cyclone during Saturday, in North Italy with a slight movement to the North Adriatic Sea during the night. Steep lapse rates and quite moist environment suggest the formation of CAPE in a large part of level 1 area with values between 200 - 400 J/kg. We expect the formation of scatter thundery showers that will later be organized into multicells, especially in the East coast of Adriatic Sea during the passage of a cold front. Excessive rain will be the main threat (PW 30-35 mm) but also severe wind gusts as 850 hPa winds will exceed the 25 m/s. Strong DLS and mid-level shear could easily organize the storms into multicells or even supercells in the high lightning probability area. LLS shear of more than 10 m/s, SREH0-1km of >400 mē/sē and low LCL values are enough for tornado / waterspout threat. The risk is lower in west coast of Italy and Corsica.
Some more scattered thunders are expected, as shown in the map, like France that will be under the left exit of a jet streak, but there is low confidence for widespread convective phenomena along the polar air mass.
