The Upper Mississippi River Basin (UMRB) is crucial for water transportation, power generation, and agriculture, among other uses. It is highly sensitive to precipitation extremes, which can significantly impact the streamflow across the entire system. Understanding projected changes in streamflow is vital for managing the basin and its economic activities. This study evaluates changes in streamflow extremes using RegCM4 downscaled climates driven by MPI and GFDL GCM simulations under historical conditions and the RCP8.5 scenario. The data were bias-corrected as part of the NA-CORDEX program. Outputs from these simulations, including daily precipitation, minimum temperature, and maximum temperature, were input into the Soil and Water Assessment Tool (SWAT) model to simulate streamflow for the UMRB at Grafton, IL, for contemporary (1981-2010) and future (2041-2070) climates. We analyze monthly extremes of high flow (upper 5th percentile) and low flow (lower 5th percentile) in Grafton discharge and investigate how extremely wet and dry precipitation periods influence and sustain these streamflow extremes. The analysis examines precursor conditions in monthly precipitation, evapotranspiration (ET), and potential evapotranspiration (PET) in the months preceding the streamflow extremes for both contemporary and future periods, with particular attention to high flows that exceed USGS flood stages. Additionally current work is being done to conduct four 25-km variant simulations of the Community Earth System Model Large Ensemble (CESM-LE) downscaled by the Weather Research and Forecasting (WRF) model and SWAT model to examine UMRB weather, climate, hydrology, and the climate change signal versus noise of unforced variability.