Storm Forecast
Valid: Tue 25 Oct 2016 06:00 to Wed 26 Oct 2016 06:00 UTC
Issued: Mon 24 Oct 2016 21:24
Forecaster: DAFIS
A level 2 was issued for NW Italy mainly for excessive precipitation, severe wind gusts and tornadoes.
A level 1 was issued for S France, N Italy and coasts of Slovenia and Croatia mainly for excessive precipitation, severe wind gusts and tornadoes.
A level 1 was issued for Spain and Portugal mainly for severe wind gusts, large hail and excessive precipitation.
SYNOPSIS
A wide ridge has formed over Mediterranean Sea where warm air masses are advected to the North as well as dust from the Sahara desert. Several short-wave troughs exist over North Europe and wide low pressure system swirls off the shore of Portugal with no significant change of its center. The advection of warm and moist air masses towards, the coasts of Spain, France and Italy in association with a jet stream aloft are going to enhance probabilities of DMC events.
DISCUSSION
.... France, Italy and coasts of Croatia-Slovenia ....
Several thermodynamic ingredients overlap over this area of interest, where LL advection of moist air masses and steep mid-level lapse rates create some hundreds of CAPE. Especially around the Gulf of Genoa, NWP models forecast MLCAPE up to 1200 J/kg overlapping with 20-25 m/s DLS and 15-20 m/s 0-3km bulk shear, but also they predict a vorticity lobe in the mid-levels crossing the area after 12z. The main threat for all the aforementioned countries will be excessive precipitation from multicells or supercells and training convection. Clustering of storms over France may lead to limited coverage of thunderstorm activity but yet the threat of excessive precipitation is high over the Rhone valley and westward slopes of the Alps. High resolution models indicate the CI NE of Corsica in the afternoon where strong kinematics enhance the potential of supercell development. PW exceeds 30-35 mm and NCAPE is not expected to exceed 0.2 m/sē, so large hail is difficult to form. The main threats will be excessive precipitation and severe wind gusts as the storms will travel fast and winds at 850 hPa may exceed the 17 m/s according to latest WRF runs. A level 2 is issued to highlight the areas with the most serious threat for severe weather occurrence. LLS is also of serious concern during Tuesday afternoon, where it overlaps with SBCAPE and in case of a supercells we may have the formation of one or two tornadoes, apart from waterspouts.
.... Portugal and Spain ....
The low pressure system SW of Portugal pushes warm and moist air masses towards the coasts of the country, where some hundedrs of CAPE are forecast and persistent storms are already affecting this part of Iberian Peninsula. For this part of level 1 area the main threat will be excessive precipitation and severe non-convective wind gusts. For Central and SE Spain, steep mid-level lapse rates and moist PBL create about 500 J/kg of MUCAPE and any storm that will manage to form into this strongly sheared environment, may become severe by producing large hail and severe wind gusts. These threats are mostly expected in the areas highlighted by 50% of lightning probability. The thunderstom activity should diminish after 21z.
