Storm Forecast
Valid: Sun 12 May 2013 06:00 to Mon 13 May 2013 06:00 UTC
Issued: Sun 12 May 2013 02:23
Forecaster: VAN DER VELDE
A level 1 was issued for eastern Poland and eastern Lithuania mainly for large hail.
A level 1 was issued for northern Algeria mainly for large hail and severe wind gusts.
SYNOPSIS
Slight low pressure is present over the Balkan at the surface. In the mid levels, a large trough stretches all the way from a North Atlantic low to Greece, with a marked cold pool passing from Netherlands to Germany and another small trough moving into northern Italy during the evening. Cooler air is advancing eastward into central Europe and Italy. Warm dry air from the high pressure over Ukraine/Russia flows westwards. An elongated convergence zone exists in the middle, with relatively warm, unstable air. Most of the indicated thunder areas do not have sufficient vertical shear to support severe weather threats, although an isolated marginally large hail event cannot be excluded. Over the southern Balkan storm motion will be slow, and local flash floods can occur. Adriatic/Ionean/Aegean areas might see an isolated waterspout.
DISCUSSION
...Poland and Lithuania region...
The convergence zone with reasonable CAPE (500-1000 J/kg) forms a cyclonic circulation here where northeasterly surface winds meets southwesterly mid level winds, creating 15-20 m/s 0-6 km shear and more than 200 mē/sē SREH if cell motion is northeastward. Supercells can result from this, and will primarily cause large hail and isolated severe wind gusts. Upper support is lacking a bit, but this may prevent formation of an organized linear mesoscale convective system.
...northern Algeria...
Uncapped CAPE and steep lapse rates are available under the strong subtropical jet stream. GFS predicts values of 300 mē/sē SREH and cloud bases of 2500m. Supercells with large hail and severe gusts )with dust) are likely.
