A new software system for assessing the uncertainty in short term river stage forecasts has been developed at the Office of Hydrologic Development of the National Weather Service (NWS). This method explicitly accounts for the uncertainty in the future precipitation and temperature conditions, a major portion of the uncertainty in the river stage forecasts. The method requires deriving a forecast distribution for a given deterministic forecast from the joint distribution of historical forecasts and observations. Once the forecast distribution is known, the climatological distribution is mapped into the new forecast distribution to create ensembles of precipitation and ensembles of temperature. The existing Ensemble Streamflow Prediction technique within the NWS River Forecast System is used to generate stream flow ensembles from the precipitation and temperature ensembles. Using the system, the Mid-Atlantic River Forecast Center has been producing forecast ensembles for the Juniata river basin in Pennsylvania on a daily basis since July 2002. Presented here are some the results for the Juniata basin obtained during the Summer and Winter of the year 2002.