Comparison of calibration techniques for a limited-area ensemble precipitation forecast using reforecasts

The calibration of the precipitation forecasted at high resolution is currently a challenge for the ensemble community working with Limited Area Models. Here, the potential of using reforecasts to achieve this goal was investigated. Different calibration techniques were tested. The impact of the application of these techniques to the precipitation forecasts provided by a Limited-area Ensemble Prediction System was verified over the Emilia Romagna Region (Northern Italy), Switzerland and Germany. The results revealed a beneficial impact of the calibration process for Switzerland and Germany; rather, no significant improvements were obtained for Emilia Romagna. As the model error is likely to have a systematic dependence on geography, orography and flow direction, weather-regime dependent correction functions should be generated for improving the calibration strategy.