Valid: Sat 09 Apr 2016 06:00 to Sun 10 Apr 2016 06:00 UTC
Issued: Sat 09 Apr 2016 00:43
A level 1 was issued for parts of W Russia mainly for large hail, severe wind gusts and in lesser extent for an isolated tornado event.
SYNOPSIS and DISCUSSION
A section of warm and moist air mass with available thermodynamic instability covers most of the E, SE Europe and CNTRL Mediterranean. Due to a broad lowering of the pressure over Balkans and Romania, 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. Locally a hail up to 1-2cm with an accumulation of small hail is possible. An increased amount of precipitation may also occur along Croatian, Albanian and Greece coast where a convective precipitation will superimpose with stratiform type. However, due to rather low PW values (~ 25mm), the risk of flash flooding is limited.
Due to a cutting off trough in W Mediterranean area, a couple of thunderstorms are expected in the early forecast hours on the waters between Balearic Islands and Corsica. With the passage of the day, a system should move eastwardly and thanks to the PVA and thermodynamic instability, produce during a nighttime a thunderstorms over Tyrrhenian Sea.
Given equilibrium levels below -20C and updrafts reaching a graupel growth zone, a small probability for lightning within low-topped convection falls on the cold section of the trough over British Isles. Even the boundary layer's moisture is poor, a steep lapse rates (> 8 K/km) contribute to a CAPE of around 100-400 J/kg. An isolated convective mode is expected in this area.
An area where a thermodynamic instability overlaps with an edge of the jet streak (and thus where a severe convective phenomena are possible) covers part of the W Russia. Within a very steep lapse rates in mid-levels (> 8 K/km), boundary layer's moisture up to 10 g/kg, but rather weak low-level lapse rate (2m temp. of around 15C), a CAPE up to few hundredths of J/kg develops in the afternoon hours. NWP models contain a poor signal in producing CI, but if yes, the environment is conducive for producing supercell thunderstorms (DLS ~ 20 m/s, SRH ~ 200 m2/s2). If the CI will begin, one or two supercells capable of producing large hail (up to 3-4cm) and severe wind gusts are possible. Due to increased LLS (~ 10 m/s), low-level SRH (~ 150 m2/s2) and low LCL, an isolated tornado event cannot be ruled out. The threat for the severe weather should significantly decrease after 18 UTC due to a drop in thermodynamic instability and a transformation into elevated convection.