Seasonal Volume Forecasts Using Ensemble Streamflow Prediction for the 2007 Water Year Steve King, 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  Statistical Water Supply  Seasonal Volumetric Forecasts Regression techniquesRegression techniques  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 Suppy 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 ‘06) Jan-Jul Volume Forecasts Jan-Jul Volume 30 yr Normal 51 MAF 2006 Jan-Jul Cumulative Obs Volume 54 MAF – 106%

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

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  Soon to incorporate climate forecasts

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

 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 Standard ESP Forecast Median = 3.44 KAF CPC Adjusted ESP Forecast Median = 3.22 KAF 30yr Norm = 3.55 KAF 2007

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