1. Long Term Streamflow Forecast Validation Western Washington Watersheds Water Year 2004 If only we’d seen this one coming... Pascal Storck 3TIER Environmental Forecast Group

2. Water Year 2004: Outlook Outlook in fall 2003 (last year’s CIG meeting in Kelso): ENSO Neutral: Expect equal probabilites of past streamflows: Trend toward historic mean Colombia River Forecasts Guidance from UW, NRCS etc - expect near normal What actually happened?

3. Water Year 2004: An interesting year Seattle breaks one day precipitation record in October, Back to back huge flood events on the Skagit Watershed Great start to ski season in November: Stevens open by Thanksgiving Somewhat dry - warm winter: Low snow accumulation at mid elevations Most Rapid snowmelt ever recorded in March - April Hot Summer Summer Streamflow significantly below normal Record amounts of Precipitation in August and September - very high streamflow Long Term Climate and Streamflow Forecasting is a very humbling business for all of us.

4. So how did our streamflow forecasts perform in Western Washington during such an interesting year.

5. First Relive the (Glorious) Past: Results for Water Year 2002 - 2003

6. Average May to Sept Inlfow (cfs) Boxplots of the May to September Average Ross Lake Inflow Forecast Compared to Climatology Water Year 2002

7. Water Year 2003

8. Water Year 2004

9. Water year 2004 Climate forecast ENSO Neutral: Hedge toward normal Climatology

10. Dec ‘03 Looking Normal Early Feb ‘04 Slightly Low Mar ‘04 A full St Dev low Apr ‘04 Record Low WY 2004

11. Predicted Climatology Water Year 2004 Seattle City Light Ross Reservoir Inflow Forecast

12. We’ve shown results for SCL for 3 years now... It’s time to showcase some new clients.

13. New Long Term Streamflow Forecast Clients in 2004. Tacoma Power: Mayfield Project: Cowlitz River PacifiCorp: Merwin Project: Lewis River Both in the Southern Washington Cascades Highlight Tacoma Power forecast performance

14. Dec ‘03 Looking Normal Early Feb ‘04 Above Normal Mar ‘04 A full St Dev High April 21: It’s still a normal year. Is it really? WY 2004

15. Predicted Climatology Water Year 2004 Tacoma Power Mayfield Reservoir Inflow Forecast

16. Summary and Conclusions Water Year 2004 was a challenge. Forecasts were dynamic and skill came from initial state. The year started off near normal - or slightly above -and then the bottom fell out. Nevertheless, long term forecast guidance for these watersheds was more skillful than those based on snow survey data only - rapid updating based on integration of met observations (including SNOTEL) was key.