Storm Forecast
Valid: Sun 01 Jun 2014 06:00 to Mon 02 Jun 2014 06:00 UTC
Issued: Sun 01 Jun 2014 06:45
Forecaster: VAN DER VELDE
A level 2 was issued for northern Algeria mainly for large hail and severe convective wind gusts.
A level 1 was issued for Ukraine, Belarus and Russia for large hail and excessive rain.
A level 1 was issued for NW Italy mainly for large hail.
SYNOPSIS
In mid and upper levels a large cluster of low pressure areas is situated across Europe with cores near southern Spain, Adriatic Sea, western Ukraine, northern Germany, Turkey, northern Scandinavia and Ireland. The strongest lift and vertical wind shear are forecast across Algeria. At the surface level, a pronounced low is present over Ukraine, collocated with a zone of warm, humid air bounded by an occlusion front in the west and dry advancing air from Russia in the east. The largest CAPE values (>1000 J/kg) are reached over eastern Ukraine.
Slight CAPE is present elsewhere as indicated, and is weakly capped.
DISCUSSION
...Algeria...
The strong lift from the advancing upper low meets relatively modest CAPE (<500 J/kg) but under very strong deep layer shear (30 m/s) and 0-3 km storm-relative helicity (300-450 mē/sē). This strongly favors supercell storm mode (perhaps clustering into an MCS) with large hail and severe wind gusts, if the initial updraft attempts can be sustained. The Saharan dry air entrainment and cap is more problematic to the south and east, so that most likely just the incoming lift from the west triggers storms.
...northwestern Italy...
Under a band of ascending motion from the German upper low moving to the south, a modest CAPE signal (in GFS) combines with moderate deep layer shear (15 m/s). This and the effects of the terrain on the flow can briefly create supercell or multicell storms with a chance of large hail.
...Ukraine, Belarus, western Russia...
Low LCLs and weakly capped profiles with relatively high precipitable water combined with weak storm-relative winds in the central Ukraine part of the area suggest chances of excessive precipitation, particularly due to training of storms. The southwest and eastern border of the area have moderate vertical shear which may favor isolated large hail. Along the Russian border the 0-1 km shear appears good for tornado chances, but this overlaps with the presence of CIN. More low-level veering is predicted by GFS east of Estonia without a cap, so an isolated supercell with tornado is not ruled out.
