SINGLE EXPONENTIAL SMOOTHING METHOD IN FORECASTING NUMBER OF RAINY DAYS PER YEAR BY DISTRICT OF OBSERVATION STATIONS LAMONGAN
In Lamongan regency, East Java, especially in the rainy season, the observation station recorded every year the average rainy day is still around 130 rainy days. This is very important for some sectors, especially agriculture, fisheries, industry and other business sectors in the region. As many methods of forecasting are used in predicting a situation. Then the need for a data forecasting system to determine the number of rainy days per year according to Lamongan district observation station using Single Exponensial Smoothing method in order to assist the rain observation station in predicting the results of his observations every year.
From the results of this study it can be concluded that the result of forecasting with the smallest error value obtained at observer station Prijetan when forecasting using α value of 0.7 and forecasting results with the largest error value obtained at observer station Mantup when done prediction using α value of 0.1. From a total of 25 observer stations, the best forecasting results were obtained when using α values of 0.9 for 9 stations, namely Sukodadi, Bluluk, Baru / Girik, Pucuk, Babat, Brondong, Bluri, Pangkatrejo and Karanggeneng, as the 9 observer stations have day data The rain is steep.