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 Kevin Berghoff, 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 • 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 • Statistical Water Supply • Seasonal Volumetric Forecasts • Regression techniques

5. Statistical Water Supply 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. 2006 WS Forecast Recap 30 yr Normal 3.55 MAF 30 yr Normal 63 MAF Jan-Jul Volume Forecasts Jan-Jul Volume Forecasts Oct 06 ESP FX 3.5 MAF – 99% 2006 Obs volume 3.5 MAF – 99% 2006 Obs Volume 69 MAF – 106% Oct 06 ESP FX 63.8 MAF – 101% 30 yr Normal 30 MAF 30 yr Normal 107 MAF Jan-Jul Volume Forecast Jan-Jul Volume Forecasts Oct 06 ESP FX 98.5 MAF – 92% Oct 2006 ESP FX 26.7 MAF – 89% 2006 Obs Volume 115 MAF – 107% Oct 06 ESP FX 26.7 MAF – 89% 2006 Obs Volume 32.2 MAF – 107%

10. 2006 ESP/Regression WS Comparison

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 • Also incorporating CPC climate forecasts

12. 57412 KAF-91% 98130 KAF - 91% 29470 KAF-98% 2007 Outlook – ESP Forecast 3351 KAF-94%

13. Climate Discussions • CPC ENSO Discussion – Oct 5, 2006 • …Typical El Nino conditions are likely to develop over North America during the coming winter season…warmer than average temperatures over western and northern U.S. … drier than average conditions in the PNW… • UW Climate Impacts Group – Sep 13, 2006 • …Weak El Nino conditions are likely to continue, and possibly intensify, into early 2007… • International Research Institute for Climate Prediction – Sept 20, 2006 • …thresholds for El Nino conditions (SST anomolies) have been crossed recently…probability of developing El Nino conditions is 55-60% by the end of 2006…and that of maintaining neutral conditions is approximately 40%...

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

15. CPC vs Non-CPC ESP ForecastDworshak Reservoir Inflow Example 2007

16. CPC vs non-CPC ESP ForecastJan – Jul Volume Comparison

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

18. New Web Tool

19. New Volumetric Forecast Display Tool New Web Tool

20. New Web Tool

21. New Web Tool

22. New Web Tool

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