The October 2011 devastating flash flood event of Antalya: triggering mechanisms and quantitative precipitation forecasting

Abstract

The Gulf of Antalya was affected by very heavy precipitation (238 mm in 6 h) that resulted in a devastating flash flood on 9 October 2011. Analysis of numerical model products, based on diagnostics and comparison with conventional and remote-sensing observations, indicates that the remarkable amount of accumulated precipitation was strongly modulated by mesoscale effects induced on the synoptic-scale flow. There was a sustained co-alignment of an upper-tropospheric tongue of high potential vorticity (PV) over a pre-existing low-level baroclinic region. Thermal advection by the low-level circulation at 925 hPa formed a warm equivalent potential temperature (EPT) anomaly ahead of the PV-streamer, enhancing the effects of pre-existing warm-moist advection. Interaction between the PV-streamer and thermodynamic processes at low levels set the scene for an enhanced dynamical feedback from the warm low-level anomaly to upper levels, and the tighter coupling led to further reinforcement of low-level warm-moist advection. A southwesterly low-level jet (LLJ) with high EPT transported conditionally unstable and moist air from the relatively warm Mediterranean Sea, and the sustained northeastward moisture flux was directed toward the concave segment of the Taurus Mountains. Quantitative precipitation forecasting (QPF) of the phenomenon is explored using the recently developed mesoscale ensemble prediction system - which is constructed by combining the Weather Research and Forecasting model with various ensemble approaches. QPF studies give the timing, location and amount reasonably well 72 h in advance. Sensitivity experiments have been carried out to explore the mesoscale aspects of the precipitating structures and their dependence on orography, surface (sensible and latent heat) fluxes and latent heating due to convection.