1. NOAA’s National Weather Service National River Forecast Verification System NOAA Science Advisory Board Meeting July 16, 2003 Gary Carter Director, Office of Hydrologic Development

2. NOAA’s National Weather Service Verification of River Stage Forecasts Started April 2001 for 194 locations nationwide Data archived at each River Forecast Center Mean Absolute Error (MAE) results stratified by: Flow Level - above and below flood stage Forecast Lead Time - 6 to 72 hours Forecast Lead Time - 6 to 72 hours River Response to Rainfall - fast, intermediate, and slow Note: more robust verification methodology will be introduced, data points are not statistically independent

3. NOAA’s National Weather Service River Forecasting Challenges: Conceptual Catchment Representation Evapo- transpiration Rainfall Infiltration Soil moisture storage Groundwater storage Fast flow Percolation Slow flow Base flow Total flow

4. NOAA’s National Weather Service Above and Below Flood Stage Sample Sizes April 2001 to March 2003

5. NOAA’s National Weather Service Below Flood Stage Forecasts Mean Absolute Error (feet) April 2001 to March 2003

6. NOAA’s National Weather Service Above Flood Stage Forecasts Mean Absolute Error (feet) April 2001 to March 2003 Above Flood Stage Forecasts Mean Absolute Error (feet) April 2001 to March 2003

7. NOAA’s National Weather Service Summary of Verification Issues MAEs range from about 0.2 to 2.5 feet and generally increase with forecast lead time NWS River Forecast System performs well for locations below flood stage and for Slow rivers with 3 days, or more, delay between heavy rainfall and the crest (e.g., Ohio River at Evansville, IL) Intermediate Rivers with 1 - 2 days between heavy rainfall and crest (e.g., Russian River at Guerneville, CA) are difficult to forecast above flood stage: investigate impacts of improved quantitative precipitation forecasts and deploy high resolution hydrologic models

8. NOAA’s National Weather Service On-going Projects Water Predictions for Life Decisions Probabilistic River Forecast Verification Methodology - University of Arizona Evaluation and Enhancement of River Forecast Verification Procedures – NWS PhD Dissertation