Storm Forecast
Valid: Thu 31 Dec 2009 06:00 to Fri 01 Jan 2010 06:00 UTC
Issued: Wed 30 Dec 2009 21:09
Forecaster: GATZEN

A level 2 was issued for western Portugal, Sardinia, Corsica, central Italy, and western Croatia regions mainly for excessive rain and to a lower extend for tornaodes.

A level 1 was issued for southern Iberiy and the north-west Mediterranean mainly for excessive rain and to a lower extend for tornadoes and severe wind gusts.

SYNOPSIS

To the south of low geopotential over Europe, a strong mid-level jet affects the Mediterranean. A very strong jet streak will travel eastward at the flank of an intense short-wave trough and is expected to reach the central Mediterranean late in the period. Strong cyclogenesis is forecast over southern France, and excessive precipitation will affect portions of the north Mediterranean region.

DISCUSSION

Southern Iberia and north-west Mediterranean

An active forecast period is forecast given a broad frontal zone will strech across the north-west Mediterranean that will slowly spread southward. In the warm sector, a moist and warm air mass is present. Latest soundings indicate rich low-level moisture and steep mid-level lapse rates, creating CAPE in the order of 200 J/kg. On Thursday, models predict increasing lift ahead of the approaching jet streak, and increasing lapse rates will likely be associated with CAPE. Focus of lift is forecast along and just north of the frontal boundary, where stratiform precipitation with embedded thunderstorms will likely evolve. Excessive rain is forecast especially where upslope flow will be present. Given strong vertical wind shear, storms will likely organize, and shallow mesocyclones are not ruled out, capable of producing tornadoes. Late in the period, the chance of severe wind gusts will also increase given the strong low-level winds at the southern flank of the low pressure centre.