Storm Forecast
Valid: Mon 19 Sep 2016 06:00 to Tue 20 Sep 2016 06:00 UTC
Issued: Mon 19 Sep 2016 02:36
Forecaster: VAN DER VELDE
A level 2 was issued for Greece to Moldova mainly for excessive convective precipitation, tornadoes, large hail and severe wind gusts.
A level 1 was issued for S Greece and W Turkey mainly for tornadoes and severe wind gusts.
A level 1 was issued for Hungary, W Balkan and Adriatic Sea mainly for excessive convective precipitation and spout-type tornadoes.
SYNOPSIS
A large low pressure system causes unstable weather in southeastern Europe while an Atlantic ridge extends across western and northern Europe. The low can be divided into a cold air and a warm air advection regime. The latter is the case in Greece, Bulgaria, W Turkey and SE Romania, while Italy, western Balkan and Hungary are in cooler but still warm wet-bulb potential temperature conditions. The Saharan Air Layer with steep lapse rates extends over Greece and Turkey to N Bulgaria. This feature associates also with low relative humidity at low levels resulting in high lifting condensation levels. But also significant inhibition over much of the Aegean Sea.
A shortwave mid level trough focuses dynamic lifting over the region SE Italy - NE Greece.
DISCUSSION
...Hungary/Romania to Bosnia and Adriatic Sea...
Moist airmass with slight CAPE, weak capping, weak vertical shear environment and slow predicted storm motion vectors allow isolated excessive convective precipitation events. Waterspouts can be observed over the Adriatic Sea below convection along surface convergence lines.
...Albania, Greece, E Serbia, Macedonia (FYR), Bulgaria and E Romania...
A jet stream positioned over the frontal zone and warmest air mass creates 15-25 m/s deep layer shear (0-6 km) and 150-200 mē/sē 0-3 km SREH over this large region, locally higher. The inland region should have quite high cloud bases supporting stronger/broader updrafts. MLCAPE maxima of 1500-2000 J/kg advect onto the southern Balkan coasts, at night the western Turkey coastal region. The rest will have about 500-1000 J/kg MLCAPE. The sheared environment likely will produce a number of supercells besides multicellular clusters, and is likely to produce large hail and severe wind gusts. At the coast the storms may persist and move slowly and create a larger excessive rain threat.
A threat of tornadoes is present thanks to 10-15 m/s 0-1 km shear particularly present in GFS for S Greece and W Turkey, where also 25 m/s propagation speed (Corfidi vector) can cause severe wind gusts.
The region E Romania and N Black Sea will get 300 mē/sē SREH in a moist environment. Supercell severe weather phenomena will combine with larger chances of excessive convective rainfall. It is less certain how much initiaion there will be in Bulgaria, S Romania and E Greece, but ingredients could allow more than isolated severe weather.
