The National Center for Atmospheric Research will undertake a comprehensive assessment that quantifies and documents the major sources of uncertainties in hydrologic monitoring and model-prediction products. The goal of this work is to quantify the effects of different sources of uncertainty on different types of hydrologic forecasts used by the U.S. Army Corps of Engineers (USACE) water managers for different forecast time horizons and different forecast initialization times and for the different hydroclimates where USACE operates.