Obtaining representative meteorological data for watershed scale hydrological modeling can be difficult and time consuming. Data scarcity has been a huge problem in modeling the water resources of the Upper Blue Nile basin, Ethiopia. This study evaluate the applicability of Climate Forecast System Reanalysis (CFSR) and European Center for Medium–Range Weather forecasts (ECMWF) global weather data on three watersheds (Gumara, Muger Chancho and Andit Tid) of Blue Nile basin, using the hydrological model. The HBV Light model was used to compare the performance of bias corrected CFSR and ECMWF weather with that of conventional weather in simulating observed stream flow at three river gauging stations in the upper Blue Nile basin. The effect of both datasets on the simulation was assessed using Coefficient of Determination (R2), Nash-Sutcliff Efficiency (NSE), and Percent Bias (PBIAS).The simulation of stream flow after Calibration both with the observed and bias corrected CFSR and ECMWF weather data were satisfactory and above (e.g., NSE ≥ 0.5) for all of the three watershed .The bias Corrected CFSR and ECMWF weather data also performed reasonably for the three watersheds with the Nash Sutcliffe efficiency and coefficient of determination of NSE (0.734, 0.641, 0.607 and 0.747, 0.739,0.703) and R2(0.738, 0.648, 0.509 and 0.762, 0.722, 0.711) for Gumara, Muger Chancho and Andit Tid respectively. Overall the simulation result with observed weather data performed better than the bias corrected CFSR and ECMWF weather data, but can be valuable option for data scares regions of Blue Nile Basin. Generally, using bias corrected CFSR and ECMWF global weather data is important water resource planning and managements in data scarce area of Blue Nile