Storm Forecast
Valid: Sun 10 Apr 2016 06:00 to Mon 11 Apr 2016 06:00 UTC
Issued: Sun 10 Apr 2016 06:39
Forecaster: TASZAREK

A level 1 was issued for W France mainly for the severe wind gusts, large hail, and in lesser extent for the tornado.

SYNOPSIS and DISCUSSION

Most of the CNTRL, and NE Europe is covered with rather stable polar air mass where DMC is unlikely. A deep trough W of British Isles influxes a cold air mass that over W France and parts of Iberian Peninsula results in a steepening lapse rates. Given S, SE advection of moist air in mid-levels from Mediterranean area and diurnal heating, a CAPE up to 400-600 J/kg will develop in the afternoon hours over W France and locally over Spain. Due to a favorable overlap of > 20 m/s DLS with a thermodynamic instability and QG-lift on the right flank of the trough, severe convective storms are possible in the afternoon hours over W France. NWP models indicate strongest PVA signal around 15-18 UTC and thus during these hours a thunderstorms may fire up in the level 1 threat area. Thanks to the curved hodographs resulting in a favorable SRH and low-level S moisture advection, an isolated supercells capable of producing large hail (up to 3-4 cm, especially considering steep lapse rates) and severe wind gusts are possible in the warm section of the trough (ahead of the cold front) in the late afternoon hours. Because of not high dew point depressions (~ 6-8 C) in the evening hours, and increased LLS (> 10 m/s) along with 0-1km SRH (~ 100 m2/s2), an isolated tornado event cannot be ruled out, especially if the supercells will remain isolated. Risk of severe convective phenomena will decrease in the late evening hours, when the thermodynamic instability will significantly drop. Although the thunderstorms due to a strong forcing may go one during nighttime hours, they will remain mostly elevated.

A section of warm and moist air mass with available thermodynamic instability covers parts of E and SE Europe. Due to a broad lowered pressure over Balkans, and intense diurnal heating with moist boundary layer (mixing ratio ~ 8-10 g/kg) , a widespread CI with DMC is expected during afternoon hours. Because of the weakly sheared environment (DLS ~ 10 m/s) and not significant CAPE (mostly up to 600-800 J/kg), a probability for severe convective phenomena is rather low, and below our level 1 threat criteria.

Over E Mediterranean, a passage of the shortwave trough with mid-level low is expected during a forecast hours. The best chances for TS within this system falls on the S Greece and Aegean Sea during evening and nighttime hours, where a CAPE and QG-lift will be available. However, due to a small jet streak located outside a CAPE areas (too far S of the instability zone), no severe weather phenomena is expected within this thunderstorms.