Evaluation of analog-based post-processing in Croatia for the wind gust NWP

The potential goal of weather forecast verification is to quantify the quality of given forecasts to determine the best possible setup available for the predictand tested in a certain area. Such procedure is performed to adequately select the wind gust forecasts at a 10 m height for different geographical and topographical areas of the Republic of Croatia using data from 61 stations in 2018. In addition to the raw ALADIN numerical model forecast, 3 additional forecasts based on the analog post-processing method are verified: a simple AnEn forecast, an AnEn forecast with predictor weight optimization, AnEnT, and a forecast with an additional correction for the high wind speed AnEnK.

In the analysis of wind gust as a continuous variable, the raw ALADIN forecast is the least successful in the coastal group of stations, while the analysis of wind as a categorical variable shows the deficiencies of the raw forecast in the continental group of stations. It is shown that predictions obtained by the analog method improve the predictions overall, compared to the raw ALADIN forecast. The largest improvements are achieved in the coastal group of stations, while the improvements in the continental group of stations are not as emphasized. For the climatologically more common wind gust speeds, there is a noticeable improvement made with the analog-based post-processing over the raw ALADIN NWP. The same result is shown even for the extreme events, except for the continental group of stations.

The results presented in this work suggest that all the forecasts considered are more suited to predict the bora than the sirocco wind. Overall, better post-processing results are achieved in the northern Adriatic than in the southern Adriatic. However, the relative improvement gained by the analog method is more pronounced in the southern Adriatic, where the occurrence of the sirocco wind is more frequent.

Among the forecasts obtained by the analog method, the AnEnK variant could be singled out as the best one, especially for high wind gust speed. However, the differences in performance between the three variants of the analog method are often very small.