Storm Forecast
Valid: Fri 22 Jan 2010 06:00 to Sat 23 Jan 2010 06:00 UTC
Issued: Thu 21 Jan 2010 21:41
Forecaster: TUSCHY

A level 2 was issued for the coast of SW Turkey mainly for excessive rainfall.

A level 1 surrounds the level 1 mainly for excessive rainfall and tornadoes.

A level 1 was issued for Crete mainly for tornadoes.

SYNOPSIS

A sharp short wave over Greece rounds a cold-core vortex and lifts northeastwards during the forecast, affecting Turkey. Meanwhile, the cold-core vortex starts to sink southwards towards the Ionian Sea, keeping its structure and strength. Another perturbation approaches Portugal during the end of the forecast, but won't have any significant affects until 06 UTC. Ridging covers west/central Europe, whereas the stout/persistent cold high block persists over NE-Europe.

DISCUSSION

... Coast of SW / S Turkey and Cyprus ...

A sharp trough enters the Aegean Sea in the morning, before shearing /opening up towards the northeast. This scenario is still well advertised by the models with minor discrepancies, mainly in respect of the strength of the attendant surface depression. The sheared trough gains a highly negative tilt, which creates a coupled jet configuration over Turkey between the polar front jet and a developing streak in the supergeostrophic environment along the NE part of an evolving ridge over NE Turkey. A broad shield of high-level divergence is the result, crossing Turkey from SW towards NE. This upper support overlaps with an active baroclinic zone in form of a northward pushing warm front, which crosses SW/W-Turkey until 18 UTC. The main attention for excessive rainfall arises along the coast, where the slope of the topography increases from sea level to 1-2km AGL. A 20m/s LLJ with a normal component to the coast advects abundant moisture towards the coast, especially, when the LL trajcetories veer from south to southwest, which increases the fetch over 16°C ( ) SSTs. Cross sections along the SW coast of Turkey reveal a deep column of moist air and impressive lift at noon and that's the time frame, where maximized precipitation amounts are forecast in the level 2 area. A backbuilding cluster of storms is a likely scenario with training storms and / or clustering along the coast. A sharp level 1/2 gradient was used, as complex terrain well inland precludes any organized activity. In addition, CAPE decays ashore and a broad shield with moderate, stratiform rain will be the most likely scenario - assisted by the diffluent upper streamline pattern and moderate, isentropic lift. Next to the rain risk, an isolated tornado event is possible especially along the SW coast, where the center of the surface depression comes ashore with additionally ageostrophic deflection next to the friction in the BL. In addition, quite warm waters along the coast enhance the LL temperature gradient, favorable for spin ups beneath stronger updrafts. It will take some time before all showers/thunderstorms exit the forecast area - probably until 21-00 UTC.

During the late afternoon hours, the complex of showers/storms spreads eastwards,out of the forecast area. The NE-ward moving trough axis will affect Cyprus and the S-coast of Turkey during the night hours, which should keep thunderstorm activity alife along the coast ... at least until midnight. As the trough opens up, a broad warm sector covers central/east Turkey with veering winds causing an extensive area with enhanced directional shear. Some weak elevated instability signals are forecat well inland, but main activity will stay confined along the coast, where strong rainfall persists at least until midnight. In addition, gradually increasing LL CAPE hints on a waterspout/tornado risk along the coast and over Cyprus. Midnight onwards, convection loses organization with showers, thunderstorms spreading eastwards.

... Crete until 15 UTC ...

Placed in the warm sector, thermodynamics are good for scattered showers/thunderstorms until roughly 15 UTC, as a cold front pushes through. Shear at all levels is modest at best, so organized storms are more isolated in nature. However, outflow boundaries, coastal convergence and good LL CAPE hint on a waterspout / tornado risk. Isolated higher rainfall amounts are possible in the moist warm sector, but no real focus for extreme amounts is present to increase probabilities. Postfrontal air mass is dry with NVA over the area, so thunderstorm risk abates after the cold front cleared the area.

... S Adriatic Sea and the Ionian Sea ...

A cold low traverses the highlighted area from the north ( roughly 21 UTC onwards) and causes some SBCAPE build-up over the warm Mediterranean. However, the air mass had no time to recover from the past cold intrusion, so overall activity may be limited, despite rapidly steepening mid-level lapse rates. An isolated spout could evolve, but there is no reason to increase probabilities into the level 1 due to the bad quality of the boundary layer. Thunderstorms spread southwards until 06 UTC.