Storm Forecast
Valid: Sat 02 Feb 2013 06:00 to Sun 03 Feb 2013 06:00 UTC
Issued: Fri 01 Feb 2013 18:02
Forecaster: PISTOTNIK

A level 1 was issued for the Tyrrhenian Sea mainly for severe wind gusts.

SYNOPSIS and DISCUSSION

The zonal flow finally starts to turn into a more meridional pattern, as warm air advection over the Northern Atlantic pushes a ridge towards Iceland and the British Isles. Downstream development leads to a rapid amplification of a negatively tilted trough over Western Europe which pushes deeply into the Mediterranean region during the forecast period. At the surface, this process is accompanied by the formation of a deep Genoa cyclone with a forecast minimum pressure around 985 hPa Saturday noon which will move eastward into the Central Adriatic region until Sunday morning.
In the range of the trough, vertical wind shear is weak throughout the troposphere, and cold mid-levels can create humble CAPE and weakly electrified showers over relatively warm water bodies. This affects the Bay of Biscay and the Western Mediterranean Sea.
The trough is rounded by a jet streak with maximum 500 hPa winds between 40 and 50 m/s in a belt from Southern Ireland via Portugal and Algeria to the Tyrrhenian Sea, which would provide a better setting for organized convection, mostly in Northwestern Spain early and along the Croatian and Montenegrin coast late in the forecast period. However, the overlap of instability and shear is limited, synoptic lift support omits these areas, and the mediocre boundary layer moisture doesn't point to an enhanced threat of heavy rain with onshore and upslope flow, either. Hence it was decided to go without any level area, even though one or two borderline severe wind or rain events may occur.
The only noteworthy severe weather threat evolves over the Tyrrhenian Sea and the Western shores of Italy in the afternoon to evening hours, when the cold front of the Genoa low pushes eastward into an environment of 200-500 J/kg CAPE and up to 30 m/s deep-layer shear. Positive vorticity advection ahead of the main trough is another player to facilitate convective initiation. A few better organized thunderstorms with a primary threat of severe wind gusts are expected in this area, which is why a low-end level 1 was issued. However, CAPE buildup in the forecast models seems rather optimistic, the setup is diffuse and storm coverage is nowhere expected to be high enough for a >50% thunder area.