Storm Forecast
Valid: Tue 13 Jun 2017 06:00 to Wed 14 Jun 2017 06:00 UTC
Issued: Tue 13 Jun 2017 06:31
Forecaster: DAFIS
A level 2 was issued for France mainly for excessive precipitation, large to very large hail, severe wind gusts and tornadoes.
A level 2 was issued for NW Spain mainly for excessive precipitation, large to very large hail and severe wind gusts.
A level 1 was issued for N Portugal, N Spain, parts of France, Switzerland, N Italy, S Austria and Slovenia mainly for excessive rainfall, severe wind gusts and large hail.
A level 1 was issued for E Ukraine and parts of W Russia, mainly for excessive rainfall, severe wind gusts, large amounts of small hail and tornadoes.
SYNOPSIS
A wide ridge over the W Mediterranean basin brings hot and moist air masses and the jet stream that extends from NW Europe towards Russia increases the vertical wind shear to unseasonably strong values. A short-wave trough over Scandinavia is associated with a low-pressure system near the surface, and its cold front is expected to leave Ukraine and enter Russia during Tuesday, pushing some moist unstable masses to the east, creating a line of thunderstorm activity. The cut-off low over S Aegean Sea is gradually fading but the low mid-level temperatures and some weak impulses will create a favorable environment for storm activity over S Turkey. The main areas of interest are highlighted with level 1 and 2 threat areas, where we do expect severe storms.
DISCUSSION
.... N Portugal, N Spain, parts of France, Switzerland, N Italy, S Austria and Slovenia ....
The low-level air masses will experience difficulties in overcoming the strong inversion cap in France, but diurnal diabatic heating will provide enough lift in the afternoon to create some storms into this highly unstable and moist environment. The best chances for CI are found in Massif Central region in France and in NW Spain. A short-wave trough is also approaching Spain from the west and it will provide additional lift. Global NWP models and limited-area models based on GFS suggest the formation of 2000-3000 J/kg CAPE over a large part of France and Spain. GFS calculates more than 15 g/kg mixed-layer mixing ratios, delta-theta-e of up to 20K in France and 14K in Spain and PW of more than 40mm. Local convergence zones in the valleys of Massif Central can contribute to CI even between 12z-15z and every storm that forms will be able to produce large to very large hail, severe wind gusts and excessive precipitation. DLS will oscillate between 15-30 m/s, wind shear 0-3km about 10 m/s and SREH0-3 100-200 m^2/s^2, so supercells are well possible. Excessive rainfall and severe wind gusts are expected in the south Alpine region of Italy, Austria and Slovenia, also in the extreme NW parts of Spain due to training storm activity even during the night. Even though LLS is not calculated to exceed 5-7 m/s, low LCL heights in the afternoon and some signals of LL directional shear, increase the probability of landspouts or a tornado event in S France.
In the early morning of Wednesday, a belt of elevated storms is expected to affect the borders of France Switzerland NW Italy, where also excessive precipitation may lead to flash flood events.
.... E Ukraine and W Russia ....
As the cold front of the low-pressure system over NW Russia moves gradually to the east, it pushes very moist, unstable air masses. In the warm sector of the front we expect storms to organize into multicells supercells, producing excessive precipitation and severe wind gusts. The vigorous LL wind field suggest the formation of tornadoes, as the LLS exceed 10 m/s and overlaps with 800 1200 J/kg SBCAPE. On the frontal storm activity and behind the front, large amounts of small hail are possible as geopotentials decrease rapidly and wind speeds decrease.
