Forecast Update
Valid: Tue 12 Oct 2010 06:00 to Wed 13 Oct 2010 06:00 UTC
Issued: Tue 12 Oct 2010 09:37
Forecaster: TUSCHY

A level 1 was issued for E-Spain, the Balearic Islands, Sardinia and Corsica mainly for excessive rainfall.

A level 1 was issued for Malta, Sicily and S-Italy mainly for large/significant hail, severe wind gusts and tornadoes (significant event possible).

SYNOPSIS

A multi-center LL depression is ongoing over the central/western Mediterranean with one depression affecting the Balearic Islands and E-Spain and the other one is about to evolve north of Tunisia. This results in a broad area of unstable conditions with scattered to widespread thunderstorm activity. No DMC is forecast for the rest of the outlook area.

DISCUSSION

... E-Spain, the Balearic Islands, Corsica and Sardinia ...

Latest synop data takes center of gradually intensifying LL depression SE of the Balearic Islands, which is in line with the northward shift (just over/ north of the Balearic Islands) of attendant deformation zone to its north. As long as this LL vortex keeps strengthening, no real relaxation is forecast reagrding the strength of this zone of deep convergence, running from E-Spain all the way to Corsica. Main risk is heavy rainfall with clustering storms, especially over E-Spain and Corsica. Overall activity decreases in intensity after sunset, as surface low weakens betimes. However, scattered showers/thunderstorms still occur in a weakly sheared environment.

... Sicily and Malta ...

Similar set-up as yesterday. A very unstable air mass works its way to the north during the following hours, overspreading Malta and Sicily. A combination of strong lapse rates/very moist BL overlap favor MLCAPE values in the range of 1500 - 2500 J/kg. Shear well above 20 m/s (3-km and 6-km bulk shear) and strong veering all support long-lived and well structured multicells/supercells. The missing ingredient again is the weak forcing as ridging resided atop of the area of interest. We went with a broad level 1 to reflect probably limited storm coverage, but any developing thunderstorm will be able to produce all kind of severe, probably significant events included. GFS remains the most optimistic model with WRF/EZ only indicating lower-end probabilities for initiation. However, all models indicate an increase of initiation probabilities around sunrise.