The NOAA GAPP Core Project is collaborating with NCEP and the University community to develop a system to produce probabilistic hydrological forecasts for lead times from a month to a year. This is an integral part of the AHPS program. The initial focus is on experimental forecasts of natural runoff. The main purpose of this system is to serve as a test-bed for hydrologic application of monthly and seasonal precipitation and temperature forecasts. If it can be demonstrated that valid long-range runoff forecasts can be produced from this system, a national NWS long-range runoff forecast product will be developed. Monthly and seasonal forecasts from CPC as well as experimental forecasts from IRI will be used together with Advanced Hydrologic Prediction Services (AHPS) ensemble pre-processors to provide the ensemble forcing for the NHLPS hydrological model(s).