Storm Forecast
Valid: Sat 10 Mar 2012 06:00 to Sun 11 Mar 2012 06:00 UTC
Issued: Sat 10 Mar 2012 06:31
Forecaster: VAN DER VELDE

A level 2 was issued for eastern Sicily mainly for excessive convective rainfall as well as tornadoes, severe wind gusts and large hail.
A level 1 was issued for eastern Tunesia mainly for excessive convective rainfall.
A level 1 was issued for surrounding Mediterranean/Ionian Sea mainly for tornado/waterspout, hail and severe convective wind gust chances.

SYNOPSIS

Low pressure systems are found over Scandinavia and the southern Mediterranean, while high pressure centers lie west of France and over the Black Sea. The north African/Mediterranean depression is an unusually vigorous one with steep pressure gradients causing strong wind fields west and north of the core and a highly baroclinic configuration causing strong vertical wind shear overlapping with a few hundred J/kg CAPE:.

DISCUSSION

At 0600, a band of convective cells north of the core has formed not long ago near Malta and the south of Sicily. It will slowly shift northwards and convection is expected to grow. Another band visible on satellite just to its north will likely start producing deep convection as well. Judging from various models, one or two convergence lines will stall over the Sicilian east coast with continuous advection and orographic lifting of moist air and storms, posing a excessive rain / flash flood hazard. A large concern on top of that is the kinematic environment. HiRLAM, GFS and some WRF models produce 0-3 km storm-relative helicity with values between 300 and 500 m2/s2, favoring supercells. Deep layer shear is best farther to the east, but 20-30 m/s 0-6 km is likely. 0-1 km shear will be over 10 m/s and LCL heights are below 800m and supportive of tornadogenesis. Large hail could also occur given the shear, but rather weak CAPE and low LCL reduce this threat to some extent. Winds above the boundary layer are stronger than 20 m/s, so downward momentum transport in convective downdrafts can cause severe wind gusts at the surface.

While center of the low remains off the map, there are some indications that convective heating will likely transition it into a warm core system, but the strong asymmetry and horizontal shearing will not allow it a long life. HiRLAM and GFS start filling the core already after 12Z.