Storm Forecast
Valid: Tue 26 Sep 2006 06:00 to Wed 27 Sep 2006 06:00 UTC
Issued: Tue 26 Sep 2006 02:02
Forecaster: VAN DER VELDE

SYNOPSIS

A cut-off low is situated over the central Mediterranean Sea, while high pressure resides over the Baltic states and the Iberian peninsula. In between, a frontal band stretches from Italy to Norway.

DISCUSSION

Organized thunderstorm activity will prevail around southern Italy and the western Balkan in the unstable airmass within the cut-off low. Within the level 1 area, two convective regimes will be present. A strong jet stream (45 m/s at 350 hPa in Trapani 00Z sounding) rounding the south side of the upper low overlaps an area of several hundred J/kg CAPE and has its left exit region near Albania.

Most intense convection is expected here, in the form of persistent MCSes, mostly remaining over coastal zones as the warm sea provides the most abundant moisture. Deep-layer shear conditions are moderate to strong, around 20 m/s (0-6 km), best from Albania southeastward. The roughness of land surfaces increases 0-1 km shear to values good for tornadoes (>10 m/s, but not overlapping with DLS), also some 300 m2/s2 SREH in GFS and NMM models. These conditions indicate potential for development of mesocyclonic storms. Flash flooding may occur with persisting convection over the Balkan coast.

In the eastern and southern half of the area, storms are expected to produce severe gusts due to the strong flow and locally dry mid-levels (best in the south), large hail, and tornadoes (waterspouts).

In the western half of the area, shear conditions and winds are weaker, low-level lapse rates steep, with deep moisture, and storms over lines of convergence may yield waterspouts.