Seasonal Volume Forecasts Using Ensemble Streamflow Prediction for the 2007 Water Year Kevin Berghoff, Hydrologist Northwest River Forecast Center

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

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)

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

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

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

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

Volume Forecasts Available at Statistical Water Supply ESP Volume Forecasts

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%

2006 ESP/Regression WS Comparison

Spring Outlook  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

2007 Outlook – ESP Forecast 3351 KAF-94% KAF-91% KAF-98% KAF - 91%

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%...

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

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

CPC vs non-CPC ESP Forecast Jan – Jul Volume Comparison Jan-Jul 30 Yr Normal-kaf Std. ESP (% Normal) CPC adj ESP (% Normal) % Diff Dworshak (94%) 3170 (89%) -5.3% Lower Granite (98%) (96%) -2.0% Grand Coulee (91%) (89%) -2.5% Dalles (91%) (89%) -2.3%

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

New Web Tool

New Volumetric Forecast Display Tool New Web Tool

Northwest River Forecast Center