Storm Forecast
Valid: Tue 05 Feb 2019 06:00 to Wed 06 Feb 2019 06:00 UTC
Issued: Mon 04 Feb 2019 21:11
Forecaster: DAFIS

A level 2 was issued for S Greece mainly for excessive convective precipitation, large hail, severe wind gusts, and tornadoes.

A level 1 was issued for S Italy, Tunisia, Greece, and Turkey for the same threats but with less spatial coverage.

SYNOPSIS

An anticyclonic Rossby-wave-breaking event will form a cut-off low over Central Mediterranean. An elongated PV streamer, which is visible in the SEVIRI WV channels, is extending from Russia all the way SW to Italy and North Africa, and it is wrapped around the leading edge of the trough over North Africa. The strong PVA seems to assist in the intensification¬ of a strong low-level vortex just south from Italy. This cyclone will be the main feature for thunderstorm activity during this outlook. The ridge over western Europe is intensifying bringing milder temperatures in the Iberian Peninsula, while short-wave troughs parade in North Europe bringing gale-force wind gusts and rain/snow in the northern parts of the continent.


DISCUSSION

.... Italy, Tunisia, Greece, Turkey ....

Strong baroclinicity has been developed after the invasion of a cold air-mass over Central Mediterranean. A well-organized cyclone near the surface has formed south of Sicily, digging large quantities of dust from the Sahara Desert. Big uncertainties arise from the contribution of the dust particles to the precipitation outputs from numerical forecast models, especially for those which are not coupled with chemistry models. Nevertheless, a cold front has already started to develop at the NE quadrant which is expected to reach the coasts of S Greece in the morning of Tuesday 05/02. The occlusion at the NW and W part of the cyclone will bring torrential rainfall in S Italy and Tunisia, most of it convective. An alarming amount of rainfall and hail is forecast for the areas marked with a level-2 and 1 threat level.

Ahead of the cold front that will hit Greece a strong overlap of high CAPE and DLS will create the perfect environment for a linearly organized convective system bringing all kinds of severe weather. The linear forecast hodographs do not show favorable conditions for tornadogenesis, but the strong low-level wind speeds and shear, eg. wind speeds 20-30 m/s at 850 hPa, may enhance locally the low-level helicity, especially near the coasts of Peloponnese. Strong to severe wind gusts are well possible during these storms, aligned on the cold front. Large hail (2-3 cm) is mostly expected near the coasts where the most pronounced CAPE will be found, but large amounts of small hail are also possible inland, due to cold wet-bulb temperatures and steep lapse rates. Locally the DLS may exceed 30-35 m/s, but CAPE should remain in the range of 200-300 J/kg, not allowing for very big hail stones to develop.

Late in the afternoon thunderstorm activity should stop in Tunisia and after midnight also S Italy should see thunderstorms leaving the coasts, and be more localized at the west periphery of the cyclone in S Ionian Sea, which may eventually become a warm seclusion in the Gulf of Sirte. Excessive rainfall threat will still be high in S and SW Turkey during the night of Tuesday and early morning of Wednesday 06/02. Behind the cold front, mid-level cold advection over the Aegean Sea will further destabilize the environment, providing favorable conditions for numerous waterspouts.