Storm Forecast
Valid: Fri 07 Sep 2007 06:00 to Sat 08 Sep 2007 06:00 UTC
Issued: Thu 06 Sep 2007 19:42
Forecaster: TUSCHY

SYNOPSIS

An omgea-like pattern has evolved and is characterized by a weaker trough over the Atlantic Ocean, a strong high pressure area over western Europe and an intense trough over SE Europe.
There are no changes over northern Europe and unsettled weather conditions will continue during the forecast period.
Spain and Portugal will heat up and stay dry, as hot desert air spreads northward.

DISCUSSION

...Strait of Otranto, eastern / central Ionian Sea, northern and eastern Aegean Sea, Sea of Marmara, Bosporus and parts of the SW Black Sea ...

Not much changed compared to yesterday. We continue to watch a weakening thermal trough over Greece and the Aegean Sea, which becomes quite diffuse during the daytime hours while another thermal trough is forecast to reach the Ionian Sea during the night hours.
The orientation of the trough axis should stay neutral, as a combination of polarfront / subtropical jet on the downstream side and a weakening, but still potent upper-level streak on its upstream side prevent any lifting. This will result in a slow eastward motion of the upper-level system, while no appreciable amplification is anticipated.

SSTs of 24°C and above are present and overspreading cooler airmass should help to release some instability, but there are some negative points.
One is the fact that the atmosphere just to the south of the cyclonic upper-level vortex remains quite warm and latest sounding reports confirm this environment.
The other point is that the airmass is pretty dry ( latest dewpoint readings are well below 10°C ). Some improvement can be expected over the Aegean Sea, the Sea of Marmara and the southwestern Black Sea region, where dewpoints reached around 15°C yesterday and could increase a few more degrees.

During the early morning hours, ongoing and developing thunderstorms over the Ionian Sea and western Greece should undergo a rapid weakening trend, as the thermal trough weakens, EL temperatures continue to warm and NVA approaches. Right now we will go with the wind shear axis as the outer border line for storm evolution and hence shear remains weak over the thunderstorm area. LL lapse rates weaken but stay supportive for a somewhat enhanced spout environment ( at least during the first morning hours ).

The attention then turns towards the N/E Aegean Sea and the Sea of Marmara. As mid-levels cool and strong forcing crosses the area, scattered thunderstorms are forecast to evolve. The majority of models hint on the possible development of an organized line of storms / a storm cluster over the NE Aegean Sea and the Sea of Marmara during the evening and night hours. DLS will be significantly enhanced ( between 20 and 30 m/s ) and storms could pose mainly a severe wind gust threat, although weak shear in the lowest 3km should preclude a more significant wind event.

Further towards the south ( eastern Aegean Sea ) the initiation is more questionable. Even with a more robust thunderstorm scenario, the risk for severe weather should be defined, as instability eases rapidly over western Turkey. Despite this fact, a level-1 was issued because of the intense DLS. The main threat are severe wind gusts.

The complex of storms will rapidly move northeastwards and will enter the Black Sea from the SW. Attendant severe wind gust risk will develop northeastwards, too.

...Most parts of the Ukraine...

Yesterday's frontal boundary over Moldova continues to slowly shift towards the E / NE, while disbanding. A broad channel of lower pressue will cover the Ukraine and widespread thunderstorm activity can be expected. Shear remains weak and although isolated multicells could evolve, a level-1 would be too aggressive. Stronger storms could contain small hail and produce gusty winds.