A região sudeste do Brasil é afetada o ano todo por sistemas transientes como as frentes frias. A incursão de sistemas frontais, além de afetar o dia a dia da população, pode causar danos e prejuízos a diversos setores da sociedade. Um modelo que é utilizado operacionalmente para a previsão de tempo no sul de Minas Gerais desde 2014 no Centro de Estudos de Previsão de Tempo e Clima de Minas Gerais (CEPreMG) da Universidade Federal de Itajubá é o Weather Research and Forecast (WRF). Em 2019, em decorrência da disponibilidade de dados do Global Forecast System (GFS) com maior resolução horizontal para a geração das condições iniciais e de fronteira necessárias como entrada ao modelo e do aumento da capacidade computacional disponível para as simulações, foram implementadas alterações no sistema em operação no CEPreMG. Assim, este estudo objetiva avaliar o desempenho do WRF na simulação de um sistema frontal que atuou no sudeste do Brasil em agosto de 2021. De forma geral, o modelo WRF simulou corretamente a posição e tempo de atuação do sistema, mas com algumas diferenças na intensidade. Isso não representa propriamente um problema uma vez que a resolução do WRF e dos dados usados na validação são diferentes.                                                                                                                                 Evaluation of the Weather Research and Forecasting (WRF) model in the operational simulation of a cold weather event in southeastern Brazil A B S T R A C TThe southeastern region of Brazil is affected throughout the year by transient systems such as cold fronts. The incursion of frontal systems, in addition to affecting the daily life of the population, can cause damage and losses to various sectors of the society. A model that has been operationally used for weather forecasting in the southern region of Minas Gerais since 2014 at the Minas Gerais Weather and Climate Forecast Studies Center (CEPreMG) at the Federal University of Itajubá is the Weather Research and Forecast (WRF). In 2019, due to the availability of higher horizontal resolution data from the Global Forecast System (GFS) to generate the initial and boundary conditions necessary as inputs to the model and due to the increase in the computational capacity available, changes were implemented in the operational forecast system at CEPreMG. Thus, this study aims to evaluate the performance of the WRF in the simulation of a frontal system that was registered in the southeastern of Brazil in August 2021. In general, WRF model correctly simulated the position and evolution of the system, but with some differences regarding the intensity. This is not really a problem since the resolution of the WRF and the data used in the validation are different.

Extreme precipitation events are becoming increasingly frequent and intense in southeastern Brazil, leading to socio-economic problems. While it is not possible to control these events, providing accurate weather forecasts can help society be better prepared. In this study, we assess the performance of the Weather Research and Forecasting (WRF) model in simulating a period of extreme precipitation from 31 December 2021 to 2 January 2022 in the southern region of Minas Gerais (SMG) state in southeastern Brazil. We conducted five simulations using two nested grids: a 12 km grid (coarse resolution) and a 3 km grid (high resolution). For the coarse resolution, we tested the performance of five cumulus convection parameterization schemes: Kain–Fritsch, Betts–Miller–Janjic, Grell–Freitas, Grell–Devenyi, and New Tiedke. We evaluated the impact of these simulations on driving the high-resolution simulations. To assess the performance of the simulations, we compared them with satellite estimates, in situ precipitation measurements from thirteen meteorological stations, and other variables from ERA5 reanalysis. Based on the results, we found that the Grell–Freitas scheme has better performance in simulating the spatial pattern and intensity of precipitation for the studied region when compared with the other four analyzed schemes.