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Radar-derived NEXRAD Process 3 (P3) data offer high spatial resolution precipitation data that might improve accuracy of streamflow simulations using watershed models. The objective of this study was to assess the performance of spatially-averaged subwatershed-specific P3 data on streamflow simulations using the SWAT hydrologic model. The SWAT model was chosen for this study to simulate the hydrologic processes in North Fork Ninnescah Watershed (2400 km2) located in south-central Kansas. A precipitation gauge station for each subwatershed was created using an area-weighted average of P3 precipitation estimates for all 16-km2 grid cells covering the subwatershed. The SWAT model was calibrated with both P3 data and precipitation gauge (PG) data from 1 January 2002 to 31 December 2008. The P3-calibrated model was validated using PG data for the same simulation period (2002-2008), and vice versa. The PG-calibrated model yielded slightly higher daily Nash-Sutcliffe efficiency (ENS = 0.40) than the P3-calibrated model (ENS = 0.35), but the yearly ENS for the P3-calibrated model (ENS = 0.80) was much better than PG-calibrated model (ENS = 0.43); percent bias was very good (<2%) for both P3 and PG calibrated models at all time scales. The P3-validated model (with PG calibration) had yearly ENS of 0.70, whereas the PG-calibrated model had ENS of 0.43. Even though the model was calibrated with PG data, the validated model with P3 data had comparatively higher ENS. The spatial representation of precipitation data by P3 improved model performance and provides evidence that NEXRAD P3 data is an improvement to precipitation gauge measurements.