Storm Forecast
Valid: Wed 09 Dec 2009 06:00 to Thu 10 Dec 2009 06:00 UTC
Issued: Tue 08 Dec 2009 23:39
Forecaster: PUCIK

A level 1 was issued for Northeastern Greece and Western Turkey mainly for excessive precipitation.

SYNOPSIS

A complex synoptic scenario is forecast with a mid-level ridge present over Southwestern Europe, building towards Scandinavia. On its east flank, a cut off low will move southward towards the Ionian Sea, surrounded by strong mid level jet. To the west, a significant synoptic change is forecast for the following days. In a strong westerly flow a short wave trough will emmerge from the cyclonic vortex present to the west of Iceland, influencing the weather over Great Britain and BENELUX during Wednesday night/Thursday morning. Following the short wave trough a ridge will start significant amlification over Western Europe with omega flow pattern establishing by Friday.

At the surface, a belt of high pressure will stretch from the Southwestern Mediterranean and Iberian penninsula, through Central Europe into Russia. To the Southeast, a shallow surface low is forecast to deepen slightly with its center over the Aegean Sea. Cyclogenesis is also forecast to occur over BENELUX during the early morning hours of Thursday, under the exit region of mid and upper level jet.

DISCUSSION

....BENELUX...

During the early morning hours of Thursday a mid and upper level disturbance is forecast to induce a cyclogenetical process over the North Sea, with first closed isobar developing by 06 UTC. At the same time, a strong upward motion is diagnosed via Q-vector forecast and advection high PV airmass behind the disturbance at upper levels. Strenghtening wind field in response to the cyclogenesis should boost the values of low layer shear, so that it reaches values over 10 m/s for this region. Wind shear in 0-6 km layer should exceed 20 m/s, so environment will be conducive to well organised deep moist convection. Very questionable variable is the availability of unstable stratification, albeit models forecast very weak CAPE values over the region ( less than 200 J/kg). It is difficult to determine the real degree of instability at the moment and even though it seems that strongly forced convective line with marginal risks of severe gusts or a tornado is possible, no level is introduced (an update might become necessary later on though).

...Northeastern Greece ...

As the surface low forms over the Aegean Sea, easterly winds with windspeeds of 15-20 m/s at 850 hPa level will have a delta over the region. A tongue of unstable airmass should form over the sea, providing a breeding grounds for the thunderstorms and showers with the help of synoptic scale forcing from the cut off low. Models produce significant precipitation amounts for this region, perhaps resulting from the upslope flow and a low level airmass convergence near the coast. It seems that embedded convection might add to the overall precipitation amounts and a Level 1 is introduced for the region.

...Western Turkey...

Coasts of Western Turkey might be up to an excessive precipitation event due to the prolonged period of thunderstorm and shower activity, lasting from Wednesday night well to Thursday. Long lasting convergence of moist and ustable airmass around the coasts should continuously initiate new cells over the area. Level 1 is introduced, even though the major portion of the convective precipitation might fall out during the Thursday forecast period.