Seasonal Volume Forecasts Using Ensemble Streamflow Prediction for the 2007 Water Year

1. Seasonal Volume Forecasts Using Ensemble Streamflow Prediction for the 2007 Water Year Steve King, Hydrologist Northwest River Forecast Center

2. Topics for Presentation • Northwest River Forecast Center: • Overview • NWRFC Long Range Forecasting Models and Products • Statistical Water Supply Forecasts • Ensemble Streamflow Prediction (ESP) • Recap of WY 2006 Forecasts • 2007 Volumetric Streamflow Outlook • New Web Tools for Users

3. Northwest River Forecast Center Total Area: 315,795 Columbia and Snake River Basins Coastal Drainages of Oregon and Washington 6 States & CANADA Support for 9 NWS Field Offices (WFOs) Grand Coulee Dam Lower Granite Dam The Dalles Dam The Willamette at Salem

4. NWRFC Forecasting Models • Statistical Water Supply • Seasonal Volumetric Forecasts • Regression techniques • NWS River Forecast System • Short, Medium, and Longterm capabilities • Generates output in deterministic AND probabilistic (ESP) formats • Variable Outputs for ESP • Adjusted Flow: similar to regression-based Water Supply (147 points) • Natural Streamflow (302 NWSRFS forecast points) • CPC Climate Adjusted

5. Statistical Water Suppy Combined Index: Observed Precip Observed Snow Observed Runoff Future Precip

6. Rain Plus Snow Melt NWS River Forecast System Model Components (simplified) Snow Model Soil Moisture/Runoff Consumptive Use River Routing Reservoir Regulation Flow and Stage Forecasts

7. Median Forecast (most expected) ESP Example showing 42 traces outcomes for The Columbia River at The Dalles, OR Traces represent ensemble of possible river flow behavior (Jan-Jul) Exceedance probability plot of flow volumes = area under each trace (Jan-Jul period) 50% Value (most expected) is comparable to WS forecasts

8. Volume Forecasts Available at www.nwrfc.noaa.gov ESP Volume Forecasts Statistical Water Supply

9. Jan-Jul Volume 30 yr Normal 51 MAF Jan-Jul Volume Forecasts 2006 Jan-Jul Cumulative Obs Volume 54 MAF – 106% 2006 WS Forecast Recap (Jan-Jul ‘06)

10. Jan-Jul Volume 30 yr Normal 107 MAF Jan-Jul Volume Forecast 2006 Jan-Jul Cumulative ObsVolume 115 MAF – 107% 2006 WS Forecast Recap(Jan-Jul ‘06)

11. Spring Outlook - 2007 • Ensemble Streamflow Prediction (ESP) • Adjusted Volume Forecasts Issued for Statistical Water Supply Points (147) • Natural Volume Forecast for all NWSRFS Points (302) • Updated weekly • Driven by: Antecedent Snow/Soil Moisture 10 day Precip and Temp Forecast • Soon to incorporate climate forecasts

12. 2007 Outlook (ESP Forecasts) 96 % of Normal (63 MAF) 96 % of Normal (107 MAF)

13. Taking Advantage of Climate Forecasts: • ESP Pre Adjustment Technique: • CPC Outlooks are used to shift distribution of model inputs (temperature and precipitation)

14. Standard ESP Forecast Median = 3.44 KAF CPC Adjusted ESP Forecast Median = 3.22 KAF 30yr Norm = 3.55 KAF 2007 CPC vs Non-CPC ESP ForecastDworshak Reservoir Inflow Example

15. ESP “Water Supply” Forecast Locations ESP “Natural” Forecast Locations ESP Products “Natural” Streamflow Forecasts

16. New Web Tool

17. New Volumetric Forecast Display Tool New Web Tool

18. New Web Tool

19. New Web Tool

20. New Web Tool

21. Northwest River Forecast Centerwww.nwrfc.noaa.gov