where Ltis the single exponential smoothing series at time t; ˛ is the smoothing constant (0 < ˛ < 1); ytis the actual yield at time t;Ltis the double exponential smoothing series at time t; Ct is the intercept of the L forecast series at time t; Ttis the slope of the L forecast series at time t;ˆyt+his the forecast yield at time t + h; h is the number of time periods a head