Evaluation of postprocessing of the numerical model forecast

Cilj verifikacije vremenske prognoze je kvantificirati uspješnost promatrane prognoze, tj. nakon što se prognozirani događaj zbio, utvrditi stupanj sličnosti između prognozirane i ostvarene vrijednosti promatrane veličine. U ovom radu prognoze se verificiraju u svrhu adekvatnog odabira prognoze udara vjetra na visini od 10 m za različita geografska područja Republike Hrvatske koristeći podatke sa 61 postaje u 2018. godini. Uz prognozu numeričkog modela ALADIN, verificirane su i 3 dodatne prognoze koje se temelje na metodi analogona: najjednostavnija prognoza, AnEn, prognoza s dodatnom optimizacijom težina, AnEnT, i prognoza s dodatnom korekcijom radi utvrđivanja uspješnosti za velike brzine udara vjetra, AnEnK. Kod analize vjetra kao kontinuirane varijable prognoza ALADIN najveće vrijednosti pogreške poprima kod obalne grupe postaja, dok se analizom vjetra kao kategoričke varijable pokazalo da prognoza ALADIN najlošije rezultate ima u kontinentalnoj grupi postaja. Pokazano je da prognoze dobivene metodom analogona većinom daju bolje rezultate od prognoze ALADIN. Najveća poboljšanja prognoza dobivenih metodom analogona u odnosu na prognozu ALADIN postignuta su pritom kod obalne grupe postaja, dok su najmanja poboljšanja postignuta kod kontinentalne grupe postaja. Kod klimatološki uobičajenih brzina udara vjetra metoda analogona uspješnija je od prognoze ALADIN. Isto vrijedi i za prognozu ekstremnih događaja, osim što prognoza ALADIN pokazuje veću točnost za kontinentalnu grupu postaja. Rezultati navedeni u ovom radu sugeriraju da sve razmatrane prognoze bolje modeliraju buru nego jugo. Iako su u konačnici postignuti bolji rezultati nakon primjene metode analogona na sjevernom Jadranu, relativno poboljšanje primjenom metode analogona više je izraženo na južnom Jadranu, gdje je češća pojava juga. Od samih prognoza dobivenih metodom analogona bi se AnEnK mogla izdvojiti kao najbolja, posebno za velike brzine udara vjetra, no razlike između rezultata tih prognoza su često vrlo malene.The goal of weather forecast verifcation is to quantify the quality of given forecast, i.e. to determine the degree of similarity between the values of forecasted and observed quantity after the forecasted event has occurred. In this thesis, the verifcation is performed in order to adequately select the wind gust forecasts at a 10 m height for different geographical areas of the Republic of Croatia using data from 61 stations in 2018. In addition to the ALADIN numerical model forecast, 3 additional forecasts based on the analog method are verifed: a simplest AnEn forecast, a forecast with additional weight optimization, AnEnT, and a forecast with an additional correction to determine performance for high wind speeds AnEnK. In the analysis of wind gust as a continuous variable, the ALADIN forecast takes on the largest error values in the coastal group of stations, while the analysis of wind as a categorical variable shows that the ALADIN forecast exhibits the worst results in the continental group of stations. It is shown that predictions obtained by the analog method mostly perform better than the ALADIN forecast. The largest improvements in the forecasts obtained by the analog method, when compared to the ALADIN forecast, are achieved in the coastal group of stations, while the smallest improvements are achieved in the continental group of stations. At climatologically prevailing wind gust speeds, the analog method is more successful than the ALADIN one. The same is valid for the extreme events, except for the continental group of stations, where ALADIN performs better. The results presented in this paper suggest that all the considered forecasts better model the bora than the sirocco wind. Overall, better results are achieved after the application of the analog method in the northern Adriatic then 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 analog method are often very small