Storm Forecast
Valid: Wed 11 Sep 2013 06:00 to Thu 12 Sep 2013 06:00 UTC
Issued: Wed 11 Sep 2013 05:47
Forecaster: PUCIK

A level 1 was issued for Northern Algeria and Tunisia mainly for large hail and severe wind gusts.

A level 1 was issued for Southwestern Italy mainly for excessive precipitation

A level 1 was issued for the Adriatics and the eastern coastline areas mainly for excessive precipitation and to the lesser degree for marginally large hail, severe wind gusts and tornadoes.

SYNOPSIS

The two main macro-synoptic features remain in form of A/ the low gepotential area, split into two separate cyclones, the most prominent one centered over Northern Germany, the other one over the southern Russia and B/ ridge over the Atlantic. In such configuration, drier northerly to northwesterly flow will affect much of Western and Central Europe, yielding mostly unfavorable conditions for DMC (apart from right below the mid-tropospheric cyclone) over much of the continetal Europe. Situation should be different over the Mediterranean, especially close to the North African coast and over the Adriatic / Ionian Sea, these areas discussed in more detail below. Generally speaking, combination of boundary layer moisture from the sea along with the passage of short-wave trough associated with the cyclonic vortex over Germany should provide

DISCUSSION

... Northern Algeria, Tunisia and adjacent coastlines ...

Combination of southwesterly flow in the mid troposphere, advecting steeper lapse rates with northeasterly flow deepening boundary layer moisture in the coastal areas should result in further destabilisation over the area. Nevertheless, a "capping layer" with significant CIN values will likely develop as well, possibly strongly limiting convective initiation. This hinderance might be overcome especially in the night hours with the approach of the trough. Conditions featuring moderate latent instability and strong vertical wind shear (with enhanced SREH) might favour some isolated supercells, capable of large hail and/or severe wind gusts, so that Level 1 seems to be warranted.

... Southwestern Italy ...

NWP shows concentrated area of initiation along the coastline with perpendicular flow, yielding possibility of a training pattern with well organised backbuilding MCS in strong vertical wind shear. Confidence in such event does not seem particularly high, but will keep a Level 1 for a possibility of local excessive precip event.

... Adriatic Sea and eastern coastline ...

Moderate to strong DLS is simulated over the region in 15 to 20 m/s of westerly flow in the 700 to 500 hPa layer along with weak to moderate latent instability, increasing towards the south. Cyclogenesis over Northern Italy should result in the southerly surface flow over the Sea, so that enhanced SREH is expected there. Two short-wave troughs will affect the region - one in the noon / early afternoon hours and one in the late evening / night hours. Best forcing should be present over the northern part of the area, where several successive rounds of DMC will be possible, with attendant threat of excessive precipitation. To the south, forcing will be less significant but conditions for severe DMC will be slightly better, with primary threats shifting more towards marginally large hail / severe wind gusts range. An isolated tornado event is not ruled out completely especially in the evening, when LLS will reach higher values.