Storm Forecast
Valid: Wed 16 Dec 2009 06:00 to Thu 17 Dec 2009 06:00 UTC
Issued: Tue 15 Dec 2009 22:50
Forecaster: PUCIK

A level 1 was issued for Turkey mainly for excessive rainfall and to the lesser extent for tornadoes.

SYNOPSIS

An omega flow pattern has established with an intense, negatively-tilted trough stretching over Eastern and Central Europe. A ridge, placed to the west will have its center over the Iceland. With split-flow pattern, southern part of the jet-stream will eject over the Mediterranean with one embedded disturbance influencing the weather over the Iberian penninsula. Another, most prominent disturbance, will move eastwards with strong forcing over Southeastern Europe/Turkey.

At the surface a belt of high pressure systems will cover Northern Europe while Southern and Central Europe will be under the influence of a broad low centered over the Aegean Sea and another low to the west of Iberian penninsula. Moist and unstable airmass will be advected northward on the forward flank of the Aegean low with numerous showers and thunderstorms developing under the synoptic-scale forcing of the disturbance.

DISCUSSION

... Turkey ...

Both GFS and ECMWF show abundant latent instability in the warm sector of the surface cyclone at 06 UTC, but its magnitude should decrease afterwards. The tongue of instability will move eastwards in relation to the movement of the mid-level disturbance. Strong forcing is expected on its forward flank. Models show a belt of enhanced southerly/southeasterly flow at 925 and 850 hPa level, perpendicular to the southern Turkey coasts. Strong coastal convergence, very moist airmass together with relatively slow storm cell motions might lead to the isolated regions recieving excessive precipitation. Region with the greatest threat will be just to the east of the forecast area border.

Besides excessive rainfall, a marginal risk of tornadoes is also forecast mainly due to the overlap of low layer shear (with values over 10 m/s) and boundary layer rooted CAPE. Also, enhanced SREH is simulated by GFS along the western and southern coasts with low condensation levels. Detrimental factor is the questionable extent of the aforementioned overlap and the lack of isolated supercellular development. Mostly clustered storms are expected, possibly forming one or more MCS. The threat should be most prominent around 03-09 UTC and decrease afterwards.

... Western Iberia ...

As the disturbance approaches, a warm and humid airmass should be present over the region, characterized by marginal CAPE values over the sea. Strong low layer wind shear is forecast, over 15 m/s inland along with a belt of very high SREH values ahead of the front. Quite strong wind gusts might occur with the dying storms that manage to move inland as 15-20 m/s flow at 850 hPa level will be present. Due to the humid airmass and weak instability, gusts should not reach severe limits though. Tornado threat should be limited by the lack of overlap of boundary layer instability and low layer shear and no risk level is issued at the moment.