Storm Forecast
Valid: Sun 17 Jan 2010 06:00 to Mon 18 Jan 2010 06:00 UTC
Issued: Sun 17 Jan 2010 05:40
Forecaster: SCHLENCZEK

A level 1 was issued for Crete and SW Turkey mainly for excessive precipitation and to a lesser extent for large hail, severe wind gusts and tornadoes.

A level 1 was issued for parts of the Aegean Sea / eastern Mediterranean mainly for waterspouts.

SYNOPSIS

On Sunday 06 UTC, the upper flow pattern is characterised by a blocking high over western Russia and a large low pressure system over Iceland / S Greenland. Ahead of an upper trough over the British Isles, a maritime polar airmass with 1 - 2°C at 850 hPa is advected into most parts of western / central Europe, leading to freezing rain in central and eastern Germany. Steepening mid level lapse rates near the trough axis over Scotland and the Scottish / Norwegian Sea will create some low-end instability that will result in showers and weakly electrified thunderstorms.

Another low over the Azores is moving towards northwestern Portugal. Near its centre, some showers and thunderstorms may develop in an airmass with 100 - 200 J/kg MLCAPE. Most of the convection will stay offshore in this period.

The focus for convective activity will be an upper low over the eastern Mediterranean. Ahead of this low, warm and unstable air is advected from N Libya / NW Egypt towards SW Turkey and Cyprus. MLCAPEs in order of 1000 J/kg are expected but deep layer shear will likely stay below 15 m/s in the western part of this thunderstorm area which is still on our forecast map. Storms are expected to be most intense outside our forecast area, i.e. the sea region between NW Egypt and Cyprus. This feature moves slowly eastward, its core should be located between Crete and Cyprus on Monday morning.

DISCUSSION

...Crete, SW Turkey...

Convective precipitation over the Aegean Sea will likely continue through the period as a plume of very moist and moderately unstable air is placed over this part of the Mediterranean. Shear at all levels is considerably weak but persistent thunderstorm activity will result in a heavy precipitation event over Crete and SW Turkey. Besides heavy rain, some waterspouts are expected to occur as rich BL moisture, weak winds and more than 200 J/kg CAPE in the lowest 3 km are forecast. The left exit region of a 25 m/s jet streak at 500 hPa points towards E Greece / S Turkey. Instability decreases towards the east, but strong QG forcing and moderate (15 - 20 m/s) deep layer shear plus slightly enhanced SRH3 (values around 150 - 200 m²/s² over Crete) are forecast which may result in some organised multicells and / or a few supercells that may pose a threat of large hail and isolated severe wind gusts. Some of the mesocyclonic storms may produce a tornado, even though LL shear will stay below 10 m/s in most places. As the upper trough moves eastward during the second half of the period, the large hail / severe wind gust threat will diminish in the evening hours. Heavy rainfall and flooding are also expected in the extreme NE parts of the Mediterranean which includes S-central Turkey and Cyprus.