Storm Forecast
Valid: Wed 02 Dec 2009 06:00 to Thu 03 Dec 2009 06:00 UTC
Issued: Tue 01 Dec 2009 22:44
Forecaster: PUCIK

A level 2 was issued for Northeastern Greece mainly for excessive precipitation.

A level 1 was issued for Greece, Macedonia, Southern Bulgaria, Turkey mainly for excessive precipitation.

A level 1 was issued for Central and Southern Greece mainly for excessive precipitation and to the lesser extent for tornadoes.


SYNOPSIS

Rather complex synoptic pattern is forecast for Europe. A highly amlified trough, stretching from Scandinavia to the Central Mediterranean, will move eastwards, slowly decaying and transforming into a cut-off low over the Aeagen Sea by Thursday morning. Strong mid and upper level jet-max is forecast around its southern flank. To the west, in a prevaling northwesterly steering flow over the Atlantic, an amplifying trough will make its way towards Western Europe with its base located over Spain by Thursday 06Z.

At the surface, a cyclogenesis is forecast over Greece, under the exit region of the cyclonically curved jet-stream. The central pressure of the surface low should be around 1004 hPa. With strong synoptic scale lift from the trough/cut-off low and unstable tropospheric profile, widespread thunderstorms are expected in vicinity of this surface low. Thunderstorms will be especially confined to the cold front associated with the surface low. This frontal system is expected to reach coast of Turkey by Wednesday 15 UTC. Large low pressure system will cover most of Western Europe with attendant fronts.

DISCUSSION

... Greece, Albania, Macedonia, Southern Bulgaria, Western and Southwestern Turkey...


This area will be under the influence of the robust trough, turning into the cut-off low, as mentioned above. Ahead of the cold front, a tongue of enhanced Theta-E airmass is expected to destabilize with around 500 J/kg of MLCAPE, locally up to 1000 J/kg. Strong synoptic-scale forcing will contribute to slight instability even in the post-frontal airmass, suggesting a widespread area of thunderstorms around the surface low. The major threat in the area will be an excessive precipitation, as a parallel stratiform, back-building MCS is possible around the cold front. With "cell-training" pattern and strong coastal convergence, locally high amounts of convective precipitation might result. The highest threat is expected over Northeastern Greece and Southwestern Turkey.

In case of Northeastern Greece, strong southeasterly flow at 850 hPa level, ranging from 15-25 m/s will have its delta over the region. Also with low level southeasterly flow impinging on the coast for a long period (actually lasting almost the whole forecast period, well into Wednesday night), numerous series of showers and thunderstorms are anticipated. Rainfall amounts of locally over 100 mm/24h migh result, much of it coming from convective activity. Low-end Level 2 is introduced for this region to highlight the area with the greatest excessive precipitation potential.

As cold front with strong flow at lower levels of troposphere ahead of it starts crossing Greece, overlap of instability with enhanced low-layer shear (over 10 m/s) is forecast. Also, low LCLs and LFCs are quite favorable for a slight tornado potential. Deep-layer shear should reach values over 15 m/s and SREH in 0-3 km layer around 150 J/kg in the frontal zone, values suggestive of well organised thunderstorms. Detrimental factor to tornadoes should be a lack of isolated development and also probably lack of instability in the boundary-layer. Despite these factors, slight chance of tornadoes will still exist in this region. The threat will be the greatest between 06 and 09 UTC.

Front will make its way towards Turkey and back-building MCS is expected to redevelop over the Aegean Sea. Western coastal areas will be under the threat of excessive precipitation but the highest risk is expected over the Southwestern coasts where a prolonged strong convergence is simulated by models along with unstable airmass.