GDAS and ECMWF: Sensitivity of initial conditions on the initiation of an intense thunderstorm in Córdoba, Argentina.

The location and timing of the initialization of convection is a key process in terms of properly forecast a severe weather event, particularly in the region around the Sierras de Córdoba (SDC) in Argentina, which is characterized by a high frequency of deep convection events. In order to analyze the sensitivity of the initialization of convection over that area, an ensemble of 12 simulations with the WRF model at convection-permitting 3 km resolution was carried out to study an intense convective system. It was constructed using different microphysics and boundary layer parameterizations and considering both analyses of ECMWF and GFS (GDAS) as initial and boundary conditions (IC and BC respectively) being the first time this type of study is done over the area. This single thunderstorm happened at SDC foothill at local afternoon hours with slow propagation to the east and two splittings. A previous analysis of the initial conditions was done noticing differences of low-level moisture between the global models. At a smaller scale, the output of the WRF model showed a difference between using different IC and BC, having a convergence line over the plains to the east of SDC for the GDAS configurations. To identify the observed cell in the simulations, a tracking algorithm using the modeled reflectivity was used resulting in a huge amount of convective initiations at both SDC hills and the plains. As regards the different IC and BC, with the ECMWF model, convective initiations were more concentrated at SDC hills with slow propagation to the east whereas, with the GDAS model, convective initiation was at both the hills and the plains with a faster velocity of propagation. In all the configurations the number of initiations was higher than the observed, having in some cases more than 20 initiations of cells. In addition, the simulations were evaluated considering the time of initiation and location. Overall, better performance of the WRF model was found with ECMWF IC and BC, as in some configurations using the GDAS model no storm was simulated. These preliminary results, remarks on the importance of an adequate selection of IC and BC when studying events of deep moist convection in Argentina.