Long term estimation of wind resource has a mean deviation of wind speed. The uncertainty associated with the wind speed has an impact on energy production, which influences wind farm’s viability, thereby, adding greater investment risk for the investors. This study answers, if an uncertainty due to long term predictions can be reduced. This is done by defining an initial process for this study, where different cases are studied and analysed initially. Results from the case studies, show that there are inconsistent time periods associated with uncertainty. A new method called, consistent period method is defined and when predictions are made using this method, has led to the reduction of uncertainty. Therefore, it is concluded that the above approach can be used for reducing uncertainty in the long term prediction using short term measured time series.