Storm Forecast
Valid: Sat 12 Dec 2009 06:00 to Sun 13 Dec 2009 06:00 UTC
Issued: Fri 11 Dec 2009 23:55
Forecaster: KOROSEC

A level 1 was issued for extreme southern Greece, eastern Mediterranean sea and SW Turkey mainly for excessive rainfall, strong winds and lesser extent for tornadoes/waterspouts.

SYNOPSIS

A large blocking pattern with strong ridge over western Europe persists throughout the forecast period, while a deep trough on its eastern flank continues spreading cold continental airmass southwards into central Europe and Mediterranean sea. West of Ibearian Peninsula, an upper-level low cuts off from the main polar vortex and moves SSE-wards towards western Marocco.

DISCUSSION

... extreme southern Greece, eastern Mediterranean sea and SW Turkey ...

Numerous disturbances are embedded in the polar jet stream around the large long-wave trough entering central Mediterranean early Saturday morning. Additionally, a few surface depressions will form near the short waves/PV anomalies. The first one over southern Ionian sea, moving eastwards during the day. Widespread ascent is expected ahead of this frontal system, placed under the favorable upper level divergence in the left exit jet region. This frontal system then moves over Crete towards SW Turkey throughout the day. Numerous showers and thunderstorms are expected to form. With moderate deep-layer shear in place (20-25m/s) overlapping with marginal instability (several hundreds of MLCAPE), organized convection is possible. The main threat will be severe wind gusts and excessive rainfall. Given the relatively high shear also in the lowest layers, a few supercells with better defined low-level mesocyclones can occur. Additionally, a tornado or two cannot be completely ruled out.

SW-erly flow over the eastern Mediterranean sea could result on persisting upslope flow and orographic precipitation over SW Turkey. There, an excessive rainfall threat will exist. Enhanced precipitation amounts are possible later towards the evening, if a cluster of storms forms near the surface low moving along the Turkish coast.

A low probability thunder line was extended over Ionian sea, western Greece and Albania where higher chances for a few isolated thunderstorms exist. Steep lapse rates, including low-level ones, suggest that a couple of waterspouts could form as well.

Another weak surface low forms over the northern Mediterranean overnight to Sunday and a few thunderstorms could form due to steeper lapse rates overspreading the sea, yielding marginal instability. Some organized convection is possible given the moderate shear in place within the jet's right entrance region.

... NW Marocco and northwards ...

During the second half of the forecast period, an upper low ejects from the main polar vortex over Atlantic sea and moves towards Marocco. A weak surface depression will serve as a focus for some convective activity, especially along the cold front. Only weak shear limits widespread deep moist convection or any organized convection.