We describe an implementation of the Variable Infiltration Capacity (VIC) macroscale hydrology model over the western U.S. at 1/8 degree spatial resolution for experimental ensemble hydrologic prediction at lead times of six months to a year. Climate forecast ensembles are downscaled from the NCEP Seasonal Forecast Model (SFM), the NASA NSIPP1 model and the CPC official seasonal outlooks. As a benchmark, we also use the VIC model to produce parallel forecasts via the well-known Extended Streamflow Prediction (ESP) method, and the ESP forecasts are further composited to provide ENSO and PDO-conditioned ensembles. The primary forecast products are: 1) monthly streamflow distributions and volume runoff statistics (similar to those provided by the NWS River Forecast Centers) for locations in the Pacific Northwest, California, and the Colorado and upper Rio Grande R. basins); and 2) westwide spatial maps of monthly forecast ensemble averages for runoff, soil moisture, and snow water equivalent (SWE). Initial testing in real-time began with bi-monthly updates for the Pacific Northwest (for winter 2002-3), and the domain was expanded to the U.S. west of the Rocky Mountains for winter 2003-4. To improve estimation of initial hydrologic conditions, we developed a simple method for assimilating observed snow water equivalent anomalies at the start of the forecast. We have also attempted to address the relative dearth of meteorological observations in the final months before the forecast start (which hampers the spin-up simulation of initial model state) using monthly interpolated monthly precipitation percentiles and temperature anomalies from a set of real-time index stations. In this presentation, we survey the methods and results (for 2003-4) of the forecasting system, and discuss some challenges inherent in real-time forecast system implementation. We also describe ongoing work to extend the system to incorporate multiple hydrologic models so as to form multi-model ensembles.