1. Cloud Seeding in the Walker River Basin Arlen Huggins Desert Research Institute Scientific basis for wintertime cloud seeding Determining the potential for increased snowfall Seeding methods and materials Detecting the impact of cloud seeding Current activities in the Walker Basin Future directions

2. Cloud Seeding: A Brief History Cold Box Experiments: 1940’s Operational Projects: 1950’s to present Research Projects –Field Studies (1960’s - 1990’s) –Statistical Experiments (1960’s and 1970’s) –Proof of Concept Experiments (1980’s- 1990’s) –New Evaluation Techniques (1980’s - ?)

3. Current Wintertime Seeding Projects

4. Concepts for Cold Cloud Seeding Winter clouds contain some water that has not been converted to ice crystals and snow Amount of supercooled liquid determines seeding potential –Ice forming particles (nuclei) required to produce ice –Natural ice “nuclei” are less numerous at warmer temperatures Artificial seeding either adds more ice nuclei or reduces the temperature so ice can form Seeded ice crystals grow and fall as snow

5. Sizes of Cloud Water and Ice Particles 1 mm

6. The Potential for Cloud Seeding Storm Frequency and Duration The Amount of Supercooled Liquid Water in a Storm Targeting Considerations

7. Seasonal Precipitation

8. Supercooled Liquid Water Remotely Sensed Microwave Radiometer Measures Cloud Liquid Depth and Water Vapor Depth

9. Supercooled Liquid Water: Integrated Effect

10. Conceptual Model for Cloud Seeding Seeding Generator

11. Modeling to Evaluate Generator Locations Seeding Simulation: Time = 1700 2/14/94

12. Modeling: Plume after 30 minutes

13. Modeling: Plume after 1.5 hours

14. Modeling: Plume after 7 hours

15. Aircraft Cloud Seeding AgI Solution Burners AgI Flares in Aircraft Flare Rack Dry Ice from an Aircraft Hopper Nighttime Flare Test

16. Ground-based Cloud Seeding DRI Remotely-controlled cloud seeding generators. Left: Mobile Unit Above: Semi-permanent Unit

17. Generator Ice Crystal Production

18. Detecting the Effects of Cloud Seeding 1. Statistical Methods California 1969:AgI Seeding0.1 mm/h Colorado 1971:AgI Seeding0.1-0.7 mm/h Montana 1986:AgI Seeding0.3 mm/h

19. Detecting the Effects of Cloud Seeding 2. Direct Observation Washington 1975:AgI/CO 2 0.15 - 0.9 mm/h Nevada 1987: CO 2 0.1 - 0.6 mm/h Montana 1988:AgI0.05 - 0.2 mm/h Colorado 1988:AgI0.1 mm/h California 1988:AgI/CO 2 0.3 - 1.0 mm/h Utah 1994:AgI0.5 - 1.5 mm/h 0.25 mm/h = 0.01 in/hr Over 35 sq. miles: Seeding effect = 18.7 acre-feet/hour For 8 storm hours = 149.6 acre-feet For 20 storms = 2992 acre-feet

20. Seeding Effects: Detection Methods Aircraft or Vehicle-mounted Particle Probes

21. Seeding Effects: Detection Methods Short-wavelength Radar Snow profiling for chemical analysis

22. Seeding Effects: Some Results A 1-hour AgI Seeding Experiment in Utah Seeded Period

23. Seeding Effects: The Aerosol Plume

24. Seeding Effects: A Radar Plume

25. Seeding Effects: Precipitation Data

26. Walker Basin Seeding Program 6 ground-based generators for 2001-02 8-9 generators by 2002-03 Aircraft Seeding over Sierra Nevada

27. Future Directions Detailed Sub-basin Evaluation of Seeding Opportunities and Impacts –SLW climatology from radiometer data –Snow Core and Chemical Analysis of Snowpack Modeling Study to Evaluate Future Ground Generator Locations –Emphasis on targeting high SLW regions –Generator network expansion Observation/Modeling Study to Evaluate Runoff Impacts