Storm Forecast
Valid: Sun 07 Sep 2014 06:00 to Mon 08 Sep 2014 06:00 UTC
Issued: Sun 07 Sep 2014 07:15
Forecaster: VAN DER VELDE
A level 2 was issued for northeastern Spain mainly for large hail and severe wind gusts.
A level 2 was issued for Algeria mainly for severe convective wind gusts.
A level 1 was issued for northern Turkey mainly for large hail.
A level 1 was issued for southern Portugal mainly for large hail.
SYNOPSIS
Upper level lows are present over the Atlantic west of the Iberian Peninsula, over the North Sea and over the Balkan and Black Sea. At the surface the main lows are situated over Spain, Germany/Poland and Turkey. Unstable airmasses are present in the region of steep lapse rates from Spain to Poland. Limited low-level moisture keeps southern France and northern Italy partially capped. A mid-level cold front of the Atlantic low moves over Spain to the east. A cold front of the North Sea low enters Germany during the evening while its warm front advances slowly over Poland. Isolated flash floods may occur in central Europe and Balkan where storm motion vectors are weak.
DISCUSSION
...Iberian Peninsula, SW France...
Very high moisture content along the east coast and in the Ebro Valley combines again with very strong lapse rates. The result is MLCAPE values of 1500-2000 J/kg with MUCAPE locally over 2000 J/kg. High cloud bases of 1500-2500 m will help support broad, strong updrafts capable of producing large hail, and cool downdrafts with chances of severe wind gusts. Vertical shear is maximized over the Ebro Valley to the Bay of Biscay, with 10-15 m/s effective 0-6 km shear. This has proven sufficient for development of supercells in the past days. Very large hail again is likely to occur in this region. Storms will likely cluster in the evening over the higher Ebro Valley and move towards France or the Bay of Biscay as an MCS with a chance of severe wind gusts.
The southwestern corner of the peninsula will be affected by a vorticity and shear maximum and should not have the very low LCLs as in the northwest, also with steeper lapse rates. Although MLCAPE is only around 500 J/kg this can result in isolated large hail.
...Turkey...
Relatively modest CAPE under 500 J/kg, particularly lacking buoyancy in upper levels is a negative factor for large hail, but should be partially compensated by the moderate LCL height of 1500 m and the shear environment of 10-15 m/s deep layer shear with SREH in northern Turkey of 150 mē/sē in support of supercells. A level 1 is issued because of the weak CAPE, although the mid level vorticity advection most likely increases the coverage of storms and could support a mesoscale convective system.
...northeastern Morocco and northern Algeria...
GFS shows intense PV disturbances and propagating low level convergence signals with upper level divergence. More than 15 m/s deep layer shear can support supercells and MCSses. With super high cloud bases over 2500m, primary threat is severe wind gusts and dust storms. But also large hail is possible given any supercells. Weak point is the actual modest CAPE values and strong entrainment of dry air. Strong are the meso/synoptic scale lifting factors.
