Storm Forecast
Valid: Sun 18 Oct 2009 06:00 to Mon 19 Oct 2009 06:00 UTC
Issued: Sat 17 Oct 2009 21:52
Forecaster: SCHLENCZEK

A level 1 was issued for the Tyrrhenian Sea, Sicily, S Italy, S Adriatic, Albania and W Greece mainly for tornadoes and to a lesser extent for large hail.

A level 1 was issued for N Adriatic mainly for waterspouts.

A level 1 was issued for E Aegean Sea, W Turkey, Bosporus region, E Bulgaria, E Romania and W Black Sea mainly for tornadoes and large hail and to a lesser extent for severe wind gusts and excessive precipitation.

SYNOPSIS

Between an upper high over the British Isles and a trough over eastern Europe, a strong northerly upper flow has established. In the wake of the trough, cold air is advected into S France and parts of the W Mediterranean. At 500 hPa, a 35 m/s jet streak stretches from C France via S Sardinia towards Sicily. In the left exit region of this jet, a small surface low developed over the Tyrrhenian Sea and is moving eastward towards Greece. Further east, a well-defined frontal boundary stretches from W Egypt via C Turkey and E Ukraine towards N Russia. As the surface low approaches Greece, advection of very moist and warm air towards the Aegean Sea, SW Turkey and the W Black Sea will continue.

A strong low pressure system near Iceland will deepen during the period, moving northward towards the Arctic Sea. In the vicinity of this low, a very strong gradient flow is expected with gusts in order of 25 - 30 m/s.

DISCUSSION

...Tyrrhenian Sea, Sicily, S Italy, S Adriatic, Greece...

Steep mid level lapse rates and quite high SSTs lead to MLCAPE in order of 200 - 500 J/kg. The area with most instability overlaps with the left exit region of a 35 m/s jet streak at 500 hPa. The airmass is weakly capped and DCVA at the left exit should be strong enough for convective initiation. SRH3 is slightly enhanced and deep layer shear in order of 20 m/s should be favourable for organised multicells and a few supercells which may produce marginally severe hail and strong wind gusts. Rich BL moisture leads to LCL heights in order of 600m and an isolated tornado may develop.

...N Adriatic...

Very steep LL lapse rates and rich BL moisture are observed in the N Adriatic. If convection develops, an isolated funnel / waterspout is likely to occur. GFS shows some signals of convective precipitation and EL cloud top temperatures near -10°C and therefore a level 1 was issued for this region.

...Aegean Sea, SW / W Turkey, Bosporus region, W Black Sea region...

In the vicinity of the frontal boundary, warm and moist air is advected northward into W Turkey and the Bosporus region. MLCAPE should be in order of 1 kJ/kg, decreasing towards the west. An approaching upper shortwave trough will provide some QG forcing in the afternoon and thunderstorms should develop. Deep layer shear and SRH are decreasing, but 15 - 20 m/s DLS and 150 - 250 m²/s² SRH3 will be sufficient for some rotating updraughts. Especially in coastal areas, LL shear is enhanced and this may allow a few tornadoes. Apart from tornadoes, storms may produce isolated severe gusts and marginally severe hail. The threat of severe weather is forecast to decrease in the second half of the forecast period.

Excessive precipitation and local flooding is likely where storms persist for several hours.