Storm Forecast
Valid: Sat 23 Dec 2006 06:00 to Sun 24 Dec 2006 06:00 UTC
Issued: Fri 22 Dec 2006 18:47
Forecaster: TUSCHY

SYNOPSIS

No significant change compared to yesterday. A developing upper-level trough south of Greenland will continue to amplify. On its downstream side, strong warm air advection will support a broad high pressure area , placed over the southern North Sea / Germany.
A cut-off low spins around over Spain and Portugal and a slow S-ward motion can be expected over the day. This system should undergo slight weakening, but another active convective day can be anticipated over parts of the Mediterranean.
The pool of very cold mid-level air is forecast to move rapidly towards the SE, crossing extreme western Russia and an isolated, weakly electrified storm can't be ruled out.

DISCUSSION

... West - / Central Mediterranean ...

Scattered to widespread thunderstorm acitvity can be expected over the area of interest.
Shear will stay too weak for any significant storm organisation.

Main concern for isolated stronger storms evolves during the late evening / early night hours just east of Tunisia. A broad and N-S elongated LL depression should develop somewhere over Tunisia, shifting leisurely towards the ENE. SSTs of 19-20°C and rapidly cooling mid-levels should create an environment with steepening lapse rates and hence a broad area of 500 - 1000 J/kg SBCAPE release.
A cluster of storms will evolve south of Sicily in a weak-shear environment.
Latest model outputs indicate that thunderstorms should stay south of Sicily as far as possible. Any marginal shift torwards the north could place Sicily under this cluster with an excessive rainfall threat due to high PWAT values and slow storm motion / possible training effects.
The same risk exists for NE/E Tunisia.

Excessive and convective related rainfall is a threat which is not incorporated in our warning scheme and no higher probabilities were issued!

A small level -1 was released over parts of Tunisia due to increasing LL shear and low LCLs just north of the surface depression. An enhanced tornado / severe wind gust threat can be expected!