Storm Forecast
Valid: Tue 20 Dec 2011 06:00 to Wed 21 Dec 2011 06:00 UTC
Issued: Mon 19 Dec 2011 23:34
Forecaster: KOROSEC

A level 1 was issued for parts of south-central Mediterranean mainly for strong/severe wind gusts, marginal hail, intense rainfalls and brief tornado threat.

SYNOPSIS

The pattern across Europe is slowly changing, where a large trough continues moving east, while upper ridge is intensifying from the WSW Europe and progressing east. By midday, a short wave trough disturbance becomes more defined on the back side of the main trough and results in a surface cyclogenesis along the west side of Italy, moving SE.

DISCUSSION

... parts of south-central Mediterranean ...

During the 2nd half of the period, deep convection is expected to take place over the Tyrrhenian sea as a response to a deepening surface low and developing frontal zone. A narrow tongue of WAA overspreads the area and storms will form mainly along the SE-wards moving cold front. As the mid-level jet around the trough intensifies, near 10-20 m/s of deep layer shear will become available. Therefore, some organized storms are possible, capable of producing marginal hail, strong to severe winds and a brief tornado or two, given the good LL shear/SREH also in the lowest layer. Storms will continue moving SE towards Sicily and S MEditerrranean overnight. Locally, some intense rain could cause flash floods as well. A level 1 seems warranted.

Elsewhere, high probability lightning line has been places over the Ionian sea and south Adriatic sea where widespread showers and thunderstorms will continue forming within the polar airmass in the wake of the dacaying trough. Severe storms are unlikely given the lack of shear, however marginal hail and a few waterspouts cannot be excluded given the good LL buoyancy and weak wind field along the numerous SFC convergence zones.