Valid: Sat 17 Jun 2017 06:00 to Sun 18 Jun 2017 06:00 UTC
Issued: Sat 17 Jun 2017 04:24
A level 1 was issued for a corridor extending from Greece up to Moldova mainly for excessive precipitation, large hail and in lesser extent for severe wind gusts.
A level 1 was issued for S Italy mainly for excessive precipitation, large hail and severe wind gusts.
A ridge with surface high covers SW Europe and is pushing towards CNTRL Europe. Tropical airmass is covering Iberian Peninsula. A broad but rather shallow mid-level trough travels with a cold front through Balkan Peninsula. A shallow low is placed over W Russia. Jet stream stretches from British Isles through S Scandinavia, E Germany, Adriatic Sea and S Balkan Peninsula. Main thunderstorm activity is associated with the trough travelling through Balkan Peninsula. Severe thunderstorm are possible on its eastern and southern flank where thanks to the support of the jet stream, a vertical wind shear is enhanced.
Surface based convection along PVA is predicted to fire up in the early hours around noon over NW Romania. Later along with the passage of the trough further storms will develop in the corridor from Greece to Moldova, and these will have the potential of producing severe weather. Environment ahead of the trough consists of 9-10 g/kg mixing ratio and roughly 6.75 K/km lapse rates. This produce not impressive ML CAPE ranging from 400 to 1000 J/kg. Only southern section of the instability zone covering Greece, FYROM and Bulgaria is supported by 15-25 m/s DLS. These storms may evolve into multicell clusters along with supercells and may be capable of producing severe wind gusts and large hail. Although storms over Romania and Moldova will be mostly in the low shear environment, they will have a potential of producing excessive precipitation due to slow storm motion and a high PW values (> 30mm). Convective precipitation superimposing with stratiform ones may also result in a local flash flooding event. The highest threat for this kind of phenomena cover E Romania and Moldova where NWP models expect high sums of precipitation. Along with diminishing instability storms should fade in the late evening hours. Nighttime activity is however possible over W Black Sea and N parts of Aegean Sea.
Thanks to relatively strong cap, this area is a bit uncertain in terms of CI. Due to lack of sufficient QG-lift models are not consistent in simulating storm activity. However, a weak flow over Apennines and a local convergence zones may help to organize thermals into updrafts. GFS expects convective cells to develop in the early afternoon hours along with intensifying diurnal heating and evapotranspiration. Under rich boundary layer's moisture (11-12 g/kg) ML CAPE develops up to 800-1200 J/kg and is covered by 15-20 m/s DLS values indicating a severe weather potential. Multicells and supercells may be capable of producing large hail, severe wind gusts and especially (given rather stationary character of the storms) heavy precipitation. Given PW values exceeding 35mm local flash flooding event cannot be ruled out. Storms should fade around 21-22 UTC when thermodynamic instability will significantly drop.