Hot-air balloon forecasts at KNMI, a validation study for the application of ECMWF and HIRLAM data

This validation study focuses on the input data quality for the special hot-air balloon forecasts at KNMI of two models HIRLAM and ECMWF. The HIRLAM model will be out-phased in 2021 and therefore replaced by ECMWF model as data source. It is shown that the ECMWF model slightly outperforms HIRLAM in predicting the wind speed and direction. This has been assessed subjectively by eighteen on-duty forecasters and objectively by analyzing statistical scores where model outcome and observations are compared. Regular wind observations at 10 m height in the Netherlands have been used as well as upper-air wind observations from the Cabauw meteorological tower and from Hot-air Balloon (HAB) tracks. The validation period is August - October 2020.