Storm Forecast
Valid: Sun 23 Mar 2014 06:00 to Mon 24 Mar 2014 06:00 UTC
Issued: Sun 23 Mar 2014 04:38
Forecaster: VAN DER VELDE
A level 1 was issued for Italy, Slovenia and Croatia for a combined chance of isolated large hail, tornado and excessive rain events.
A level 1 was issued for northern Tunesia mainly for large hail.
SYNOPSIS
A meridionally elongated upper trough stretching from arctic regions to the western Mediterranean Sea shifts eastwards. Very steep lapse rates and low dynamic tropopause (strong PV) sharply outline the cold airmass with unstable conditions favorable for deep convection. The central Mediterranean has also a warmer unstable regime with large scale lifting ahead of the approaching low dynamic trpopause (trough) and more moisture to work with. The cold front will drag first over Corsica, then progressively affects the Italian and Adriatic west coasts, mainly, by strong lifting over higher terrain. Stronger winds in the mid/upper levels create good vertical wind shear (>25 m/s 0-6 km).
DISCUSSION
...Italy and western Balkan...
At an isolated scale convective rainfall may reach more than 60 mm due to enduring convective cells riding the upwind side of elevated terrain. Deep layer shear supports persisting cells with some rotation and updraft enhancement favorable for large hail, although weak CAPE and low LCL preclude a significant hail threat. Low level shear below 1 km may be just enough at isolated scale for developing a tornado.
...northern Tunesia...
GFS and some WRF models simulate storms here in afternoon and evening, building in an environment with some 250 mē/sē 0-3 km SREH sufficient for supercells with large hail and severe wind gusts. The cold front, however, does not seem to be supported by large scale lift, rather subsidence and unfavorable differential advection of theta-w, which may lead to stabilization.
