Storm Forecast
Valid: Sat 15 Oct 2016 06:00 to Sun 16 Oct 2016 06:00 UTC
Issued: Fri 14 Oct 2016 23:54
Forecaster: TASZAREK

A level 2 was issued for E Adriatic, SW Croatia, SW Montenegro and NW Albania mainly for large hail, severe wind gusts, excessive precipitation and in lesser extent for tornadoes.

A level 2 was issued for S Italy mainly for large hail, severe wind gust and in lesser extent for excessive precipitation.

A level 1 was issued for Italy, Adriatic Sea, and W Balkan Peninsula mainly for large hail, severe wind gusts and excessive precipitation.

SYNOPSIS

Broad low covers British Isles while extensive high is placed over Scandinavia and NW Russia. Such setup enforces an advection of warm and moist airmass from CNTRL Mediterranean into CNTRL Europe. A shortwave trough travelling along far SE edge of low from British Isles creates favourable conditions for the development of DMC involving moderate instability and strong vertical wind shear. A weak jet streak supporting better storm organization stretches from Tunisia up to Hungary. Within the support of QG-lift, severe thunderstorms are expected to develop over CNTRL Italy, Adriatic Sea and W Balkan Peninsula, and form MCS in the afternoon hours. Enhanced probability for lightning is placed also SW of Ireland where within the support of QG-lift, the overlap of ~ 7 K/km lapse rates and 6-7 g/kg MIXR develops ~ 400-600 J/kg CAPE with equilibrium levels cold enough (-20C) to produce lightning. Thanks to enhanced low and mid-level airflow, convective-supported local severe wind gusts over W British Isles are not ruled out, but the probability is too low to reach level 1 criteria.

DISCUSSION

...Italy, Adriatic Sea, W Balkan Peninsula...

Thanks to the passage of shortwave trough, severe thunderstorms over CNTRL Italy and along W Balkan Peninsula coast benefit from moist and unstable environment, and develop early at around 10-12 UTC. Together with remaining MCS from the previous day, PW values exceeding 30mm, and rather slow-moving "stationary" type of convection poses a threat for excessive precipitation and local flash flooding. Increased lapse rates exceeding 7.5 K/km along with 1000-1500 J/kg CAPE and ~ 20 m/s DLS creates conditions for the development of supercell thunderstorms capable of producing large hail and severe wind gusts. The most favourable vertical wind profile for these is expected to develop along Croatian, Montenegro and Albanian coast where SRH will jump to 300-400 m2/s2. Thanks to LLS exceeding 10 m/s and 0-1 km SRH locally up to 200 m2/s2, also an isolated tornado event along the coast cannot be ruled out. Impressive values of ~ 15-20 m/s MLS may arrange convection into well-organised linear multicell cluster capable of producing severe wind gusts. Thanks to this, MCS in the afternoon hours over Adriatic is likely. Due to lower forcing factor and uncertain CI, severe thunderstorms are less likely over S Italy, but if they develop, the environment of high CAPE and high shear may quickly organize convection into supercells and result in a local event of large to very large hail. Although convective activity should drop over Italy in the late evening hours, thanks to the support of orographic and QG-lift it will remain active over W Balkan Peninsula until end of the forecast validity period.