Ensemble Flood Forecasting at the NWS Northwest River Forecast Center

For much of its history, the National Weather Service (NWS) River Forecast Centers (RFCs) have produced operational deterministic short-range streamflow forecasts designed to help communities anticipate and manage flooding. For longer lead times, RFCs have produced probabilistic hydrologic predictions to support water and energy management, but these have made little use of real-time climate forecast information. Answering a call to “complete the forecast” at the short range by adding uncertainty estimates, the NWS has developed an approach for integrating weather to climate scale ensemble forecasts from a frozen version of the current NCEP GFS model and from the NCEP CFS model into the NWS Ensemble Streamflow Prediction (ESP) approach. At the Northwest RFC, experimental ensemble forecasts using the new weather and climate forecasts are now being generated for use by water managers. The new NWS approach has the potential not only to improve water management at seasonal range, but also to change the paradigm for NWS forecasting at flood time scales. This presentation describes these advances for a case study basin the Pacific Northwest.