Storm Forecast
Valid: Sun 29 Sep 2013 06:00 to Mon 30 Sep 2013 06:00 UTC
Issued: Sun 29 Sep 2013 04:49
Forecaster: VAN DER VELDE
A level 1 was issued for parts of southern France, Corsica, Sardinia, Italy and the Adriatic coast of the Balkan.
SYNOPSIS
A low pressure system has entered southwestern Europe and maintains a warm unstable airmass over France and Italy. Blocking high pressure over southern Scandinavia is able to stop and reverse the advance of the warm airmass. The surface warm front remains near Belgium, southern Germany to Serbia, while low pressure displaces toward Italy. Later in the forecast period the massive depression over the Atlantic sends occluded fronts with warm unstable airmass in the direction of Portugal and France.
DISCUSSION
...Italy, Balkan coast...
The cold front belonging to the French low will pass over the region. There is up to 700-1000 J/kg MLCAPE present in a large area, with over 1000-1500 J/kg predicted along the southern half of Tyrrhenean and Adriatic Sea caused by steep Saharan mid level lapse rates. But the latter tends to be capped except for the northern fringe. Deep layer shear (0-6 km) ranges from 15-25 m/s with the highest values across central Italy and SW Balkan and sufficient for supercells. Storm motion can be fast (unless backbuilding over orography), 20-25 m/s with possible severe wind gusts. 0-1 km shear locally can reach over 10 m/s at the cold front and is favorable for tornado chances. Isolated large hail is possible. Corsica and Sardinia and western Italy will be affected by a second shortwave trough coming in at night.
Isolated waterspouts are to be expected in a large region of the Mediterranean.
...France...
As the flow becomes stagnant, convective cell motion is limited and locally excessive precipitation amounts may fall.
...Tunesia...
The area seems to remain capped except for the north coast. Storm-relative helicity increases over 300 mē/sē over these areas which can easily spin updrafts and create supercell thunderstorms with large hail.
