Storm Forecast
Valid: Sat 12 Nov 2016 06:00 to Sun 13 Nov 2016 06:00 UTC
Issued: Sat 12 Nov 2016 02:26
Forecaster: TASZAREK

A level 1 was issued for W Balkans mainly for excessive precipitation and in lesser extent for severe wind gusts and large hail.

A level 1 was issued for E Bulgaria, E Greece and NE Aegean Sea mainly for severe wind gusts and in lesser extent for tornadoes, excessive precipitation and large hail.

SYNOPSIS and DISCUSSION

1025 hPa high covers parts of CNTRL and E Europe. Troughs are located over W Russia, Iceland, British Isles and Balkan Peninsula. A shallow westerly moving frontal boundary stretches from Iceland through British Isles, W of France and W of Iberian Peninsula. Due to limited instability, only a marginal probability for lightning is placed in the southern section of this boundary where a CAPE increases to 300-500 J/kg in the late afternoon hours.

The main thunderstorm activity on Saturday falls on CNTRL Mediterranean and Balkans where a long-wave with a broad low and dynamic wind field passes. A mixture of 7-8 g/kg MIXR and ~ 7 K/km LR provides an instability of around 400-800 J/kg CAPE in majority over the sea surface. A jet stream stretching from Germany through Italy, S Balkan and then spreading to Romania, Black Sea and Turkey provides DLS values up to 25-30 m/s. A low-level jet with 15-20 m/s MLS and 10-15 m/s LLS extends from Sicilly, through Greece, up to Bulgaria. Although a well-pronounced upper divergent flow with solid QG-lift and strong kinematics are available, a potential for severe thunderstorms along frontal boundary is limited due to marginal (or almost absent) instability over land areas. Chances for thunderstorm producing severe weather (hail, wind) along frontal boundary will occur in the late afternoon hours over E Bulgaria, E Greece and NE Aegean Sea where a more pronounced CAPE will develop to 300-500 J/kg. Due to veering vertical wind profile (0-1km SRH ~ 200 m2/s2) and enhanced LLS (~ 15 m/s), a tornado event cannot be ruled out.

Higher chances for thunderstorms lie along W coastline of Balkans where westerly moisture advection from Adriatic Sea, orographic lift and steepening lapse rates behind frontal boundary take place. Convection will develop mostly over water surface and come ashore. Although PW values will be rather small (15-20mm), a superimposing convective and large-scale precipitation along orographic lift zones may result in a local excessive precipitation events. Thanks to increased low tropospheric airflow, a few severe wind gusts enhanced by convection cannot be ruled out. Thunderstorms will be mostly clustering into multicells, but 2-3 low-topped supercells capable of producing hail up to 2-3 cm and severe wind gusts cannot be ruled out. The same thing applies to NE Aegean Sea. Thunderstorm activity should drop in the nighttime hours after the passage of the cold front.