Storm Forecast
Valid: Wed 09 Sep 2015 06:00 to Thu 10 Sep 2015 06:00 UTC
Issued: Tue 08 Sep 2015 20:48
Forecaster: PUCIK

A level 2 was issued for E Sicily, SE Italy, S Albania, NW Greece mainly for excessive precipitation, large hail and to the lesser degree for tornadoes and severe wind gusts.

A level 1 was issued for Sardegna, NE Tunisia and parts of Italy mainly for excessive precipitation and to the lesser degree for large hail.

SYNOPSIS

A blocking pattern has evolved over Europe with a ridge over NW Europe and a trough stretching from Russia into the Central Mediterranean. Closer to the surface, a large high pressure system will be centered over Norway with cooler airmass being advected from Russia over much of Central and W Europe.

Cyclogenesis is forecast over the Ionian Sea, on the forward flank of the trough, with surface low tracking towards the S Adriatic Sea. There is disagreement between the models regarding the exact track and degree of deepening of the low. Along the frontal wave of this low, widespread DMC activity is forecast and will be discussed in greater detail below.

Much less pronounced DMC activity is forecast over parts of Central and E Europe, under the cold core of the trough. Modestly steep lapse rates may result in a few tens to 200 J/kg of MLCAPE, which may be sufficient for a few weakly electrified tstms over the region. Despite rather weak instability, rather cool environment may support non-severe hail with stronger cells.

DISCUSSION

... Tunisia towards Albania and Greece ...

Surface observations show dewpoints over 20 deg C over E Tunisia and Sicily coastlines. As the surface low forms along the frontal wave, in conjuction with the approach of the mid and upper tropospheric trough, abundant low-level moisture will be advected towards NE. Southwesterly flow at upper levels will advect a plume of steep lapse rates, contributing to high CAPE values especially over the Inonian Sea. At the same time, strong 0-6 and 0-3 km shear is forecast, reaching up to 25 m/s in the belt from S Sicily towards Albania. Actually, at the time of writing this forecast, abundant tstm activity is already ongoing east of Sicily.

Current thinking is that in the morning hours, abundant tstm activity will be still ongoing around and/or over Sicily. Activity will spread towards NE during the day. The highest threat of severe weather will shift from Sicily and SE Italy (day hours) towards Albania and W Greece (evening and night). Primary threat will likely be excessive precipitation, especially just NW and N of the surface low, where strong lift is forecast. Apart from the precipitation, large hail, severe wind gusts and also tornadoes will be possible as conditions support strong, well organised, supercell convection. The highest threat of these three phenomena will be over E Sicily and NW Greece.

There is much uncertainity on the exact tracks of the MCS with heavy precipitation and the situation will likely depend also on the initial position of storms in the morning hours. Due to this fact, we issue a broad Lvl 2, where conditions may support more widespread severe weather.

Lvl 1 is introduced where less favourable conditions are forecast and/or where initiation of tstms will be less likely.