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 Grand Coulee Dam The Willamette at Salem The Dalles Dam Lower Granite Dam Columbia and Snake River Basins Coastal Drainages of Oregon and Washington 6 States & CANADA Support for 9 NWS Field Offices (WFOs)

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

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

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

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

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

9. 2006 WS Forecast Recap Jan-Jul Volume Forecasts 30 yr Normal 63 MAF 2006 Obs Volume 69 MAF – 106% Jan-Jul Volume Forecast 30 yr Normal 107 MAF 2006 Obs Volume 115 MAF – 107% 30 yr Normal 3.55 MAF 2006 Obs volume 3.5 MAF – 99% Jan-Jul Volume Forecasts 2006 Obs Volume 32.2 MAF – 107% 30 yr Normal 30 MAF Oct 06 ESP FX 3.5 MAF – 99% Oct 06 ESP FX 63.8 MAF – 101% Oct 2006 ESP FX 26.7 MAF – 89% Oct 06 ESP FX 26.7 MAF – 89% Oct 06 ESP FX 98.5 MAF – 92%

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

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

15. CPC vs Non-CPC ESP Forecast Dworshak Reservoir Inflow Example 2007

16. CPC vs non-CPC ESP Forecast Jan – Jul Volume Comparison Jan-Jul 30 Yr Normal-kaf Std. ESP (% Normal) CPC adj ESP (% Normal) % Diff Dworshak3547 3350 (94%) 3170 (89%) -5.3% Lower Granite 30016 29500 (98%) 28700 (96%) -2.0% Grand Coulee 62899 57400 (91%) 56000 (89%) -2.5% Dalles107302 98100 (91%) 95800 (89%) -2.3%

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

18. New Web Tool

19. New Volumetric Forecast Display Tool New Web Tool

23. Northwest River Forecast Center www.nwrfc.noaa.gov