Storm Forecast
Valid: Wed 29 Sep 2010 06:00 to Thu 30 Sep 2010 06:00 UTC
Issued: Wed 29 Sep 2010 06:26
Forecaster: PUCIK

A level 2 was issued for Western Turkey, Eastern Aegean Sea mainly for large hail, severe wind gusts, tornadoes and excessive rainfall.

A level 1 was issued for Western Greece, Albania, Macedonia for marginally severe hail or wind gusts.

A level 1 was issued for Southern Bulgaria/Northeastern Greece mainly for excessive precipitation.

A level 1 was issued for the Black Sea and its coasts mainly for excessive precipitation, severe wind gusts and tornadoes.

SYNOPSIS

Rather complex synoptic scenario is forecast with amplified troughs at mid-levels of troposphere over the Atlantic and over Eastern Europe. The latter one will have a slight positive tilt and will decay to a cut off low centered over Romania by Thursday morning. Between these troughs, a ridge will stretch from France to Scandinavia. At upper levels, a jet-streak will emmanate from Southern Tunisia and stretch into Turkey and to the Black Sea.

At the surface, dominant feature will be a high pressure system over Scandinavia and at its eastern flank, cold arctic airmass will advect into Eastern and Central Europe. During the day, a low is forecast to form over the Aegean Sea, continuing towards the Black Sea, where in the left exit region of the jet-streak, further deepening is forecast. A large low pressure system is forecast over Atlantic, with little movement and change in its depth. Most of Europe will be under rather dry and cool airmass with prevailing stable conditions.

DISCUSSION

... Eastern coasts of the Ionian Sea, Greece, Macedonia, Albania, Southern Bulgaria, Aegean Sea, Turkey ...

In the prevailing southwesterly flow, a plume of high lapse-rate airmass from Northern Africa will advect over the Mediterranean Sea, where high SSTs and high dewpoint temperatures in 2 m above the sea are forecast. These factors should result in a moderate to strong destabilisation in a belt from Tunisia coastline towards the Ionian, Aegean Sea and Turkey. With CIN values over -200 J/kg and no forcing, southern half of this stretch will experience mostly no thunderstorms during this forecast period.

Towards the northeast, where less CIN is forecast along with a forcing from the surface cold front and a DCVA from the mid-level trough, convective initiation is expected. With strong southwesterly flow aloft, DLS values will reach 25-30 m/s and bulk values between 0-3 km over 20 m/s. With 40 m/s jet-streak at 300 hPa level and enhanced SREH values, conditions will be very favorable for organised convection including supercells or squall lines with bowing segments. Overlap of the moderate instability (1000 to 1500 J/kg of MLCAPE) and such favorable wind shear will be most pronounced (from the areas that will experience the initiation) over the western coastal areas of Turkey, for which, Level 2 is issued.

In the area with Level 2 (Western Turkey, Eastern Aegean Sea), numerous supercells might form, posing a wide variety of severe weather, including large hail, damaging wind gusts and with very high moisture content in the troposphere, also excessive precipitation. This threat will be maximized over Northeastern Greece, Northeastern Aegean Sea and Northwestern Turkey, where numerous rounds of thunderstorms are possibe. Due to the cyclogenesis over the Aegean Sea, low level wind shear will increase as well and close to the coastal areas where humid airmass will result in low LCLs, tornadoes can not be ruled out, especially in the case if isolated supercell manages to form. Overall threat will be the highest during the evening and early night hours and should spread progressively towards the south during the night.

Further to the north or west, less instability is predicted and lower intensity and/or coverage is forecast, which warrants a Level 1 for marginally severe hail, wind gusts and towards the east (Southern/Southeastern Bulgaria) also excessive precipitation.

...The Black Sea...

As the low pressure system will deepen over the sea during the late evening and night hours of Wednesday into Thursday, large threat of excessive precipitation will arise especially at the northwestern flank of the low, where significant lift is forecast along the warm front. Accelerating cold front in a strong low level flow reaching over 20 m/s at 850 hPa might force a rapidly advancing squall line with a threat of severe wind gusts or even a tornado if mesovortices develop within MCS.