Storm Forecast
Valid: Thu 04 Dec 2014 06:00 to Fri 05 Dec 2014 06:00 UTC
Issued: Wed 03 Dec 2014 23:05
Forecaster: GATZEN

A level 1 was issued for western and south-western Turkey mainly for excessive precipitation.

SYNOPSIS

The large amplified trough across south-western Europe starts to move eastward and weakens. A strong jet stream will affect northern Africa at its southern flank and will extend to southern Italy and Greece late in the period. Downstream, a short-wave trough moves from the Aegean Sea across Turkey.

DISCUSSION

Turkey and surroundings

Main focus will be the short-wave trough that travels across Turkey during the period. It is associated with a well-developed low-level jet that transports a moist air mass into the Aegean Sea, as latest observations with dewpoints around 15°C indicate. Differential vorticity advection ahead of the trough is currently leading to lift and steepening mid-level lapse rates, so that CAPE in the order of 500 J/kg as in latest Athinai sounding is expected. Widespread thunderstorms have currently formed along the cold front that is forecast to move across Turkey on Thursday.

Current thinking is that the cold front will affect western Turkey with numerous back-building storms that slowly spread eastward. With easterly surface winds and a strong mid-level westerly jet, around 25 m/s DLS will assist in well-developed multicells capable of producing excessive rain and locally large hail. Furthermore, a tornado is not ruled out given about 10 m/s low-level vertical wind shear and quite good low-level buoyancy. Storms are forecast to become weaker in the afternoon as the mid-level trough lifts into Turkey and the Black Sea.

Western and central Mediterranean

The large south-west European trough will slowly move east and affect the Mediterranean. With southerly low-level winds, relatively rich boundary-layer moisture has evolved, with dewpoints around 11°C. Given the cool mid-level air mass near the trough centre, instability will build and spread eastward with the trough. Numerous showers and thunderstorms are therefore expected across the Mediterranean. Weak vertical wind shear will be in place across the Sea, and severe thunderstorms are not likely except for the chance of excessive precipitation due to slow moving storms. Additionally, waterspouts are not ruled out. Due to the lack of a clear focus, a level was not issued.

Further to the south, stronger deep layer vertical wind shear can support supercells capable of producing large hail and maybe a tornado. The overall threat is quite low due to the limited low-level moisture.