Cloud Seeding Annual Report Southern and Central Utah Program 2019-2020 Winter Season Prepared For: State of Utah Division of Water Resources Utah Water Resources Development Corporation Lower Colorado River Basin States Prepared By: David Yorty Garrett Cammans North American Weather Consultants, Inc. 8180 South Highland Dr. Suite B-2 Sandy, UT 84093 Report No. WM 20-10 Project No. 19-442, 19-446 August 2020 WEATHER MODIFICATION The Science Behind Cloud Seeding The Science The cloud-seeding process aids precipitation formation by enhancing ice crystal production in clouds. When the ice crystals grow sufficiently, they become snowflakes and fall to the ground. Silver iodide has been selected for its environmental safety and superior efficiency in producing ice in clouds. Silver iodide adds microscopic particles with a structural similarity to natural ice crystals. Ground-based and aircraft-borne technologies can be used to add the particles to the clouds. Safety Research has clearly documented that cloud seeding with silver-iodide aerosols shows no environmentally harmful effect. Iodine is a component of many necessary amino acids. Silver is both quite inert and naturally occurring, the amounts released are far less than background silver already present in unseeded areas. Effectiveness Numerous studies performed by universities, professional research organizations, private utility companies and weather modification providers have conclusively demonstrated the ability for Silver Iodide to augment precipitation under the proper atmospheric conditions. TABLE OF CONTENTS Section Page EXECUTIVE SUMMARY 1.0 INTRODUCTION .....................................................................................................................................1-1 1.1 Project Extension Period..........................................................................................................1-4 1.2 Installation and Operation of Icing Rate Meters .............................................................1-4 2.0 PROJECT DESIGN...................................................................................................................................2-1 2.1 Background ...................................................................................................................................2-1 2.2 Seedability Criteria.....................................................................................................................2-1 2.3 Equipment and Project Set-Up...............................................................................................2-2 2.4 Suspension Criteria ................................................................................................................. 2-10 3.0 WEATHER DATA AND MODELS USED IN SEEDING OPERATIONS.....................................3-1 4.0 OPERATIONS...........................................................................................................................................4-1 4.1 Operational Procedures............................................................................................................4-8 4.2 Operational Summary ...............................................................................................................4-8 5.0 ASSESSMENTS OF SEEDING EFFECTS ..........................................................................................5-1 5.1 Background ...................................................................................................................................5-1 5.2 Evaluation Approach .................................................................................................................5-2 5.3 Evaluation of Precipitation in the Target Area................................................................5-4 5.3.1 Precipitation Target Sites ..........................................................................................5-4 5.3.2 Precipitation Control Areas ......................................................................................5-5 5.3.3 Precipitation Data Compilation...............................................................................5-7 5.3.4 Results of Precipitation Analyses ...........................................................................5-8 5.3.4.1 Eastern Tooele Target Results............................................................. 5-12 5.3.4.2 Primary Target Results........................................................................... 5-13 4.3.4.1 Eastern Tooele Target Results 4-16 4.3.4.2 Primary Target Results 4-18 5.4 Snowpack Water Equivalent (SWE) Evaluations ........................................................ 5-15 5.4.1 Target Area SWE Sites.............................................................................................. 5-16 5.4.2 Control Area SWE Sites............................................................................................ 5-18 5.4.3 SWE Regression Equation Development .......................................................... 5-18 5.4.4 Results of Snowpack Water Content Analysis ................................................ 5-19 5.4.4.1 Eastern Tooele Target Results............................................................ 5-20 5.4.4.2 Primary Target Results.......................................................................... 5-21 4.4.4.1 Eastern Tooele Results 4-25 4.4.4.2 Primary Target Results 4-28 5.5 Multiple Linear Regression Analyses ............................................................................... 5-24 5.6 Double Mass Plots.................................................................................................................... 5-25 5.7 Summary of Evaluation Results ......................................................................................... 5-27 i Table of Contents Continued Section Page 6.0 SUMMARY, CONCLUSIONS, AND RECOMMENDATIONS........................................................6-1 6.1 Summary ........................................................................................................................................6-1 6.2 Conclusions ...................................................................................................................................6-3 6.3 Recommendations......................................................................................................................6-4 References APPENDICES A CLOUD SEEDING SUSPENSION CRITERIA B SEEDING OPERATIONS TABLE, 2019-2020 C PRECIPITATION AND SNOWPACK CONTROL/TARGET STATIONS D PRECIPITATION AND SNOWPACK ANALYSIS RESULTS TABLES FigureE GLOSSARY OF METEOROLOGICAL TERMS Page 1.1 Seeded target areas in central and southwestern Utah..........................................................1-2 1.2 Utah average annual precipitation .................................................................................................1-3 2.1 Target areas and seeding site locations........................................................................................2-4 2.2 Portions of the Southern/Central Utah Program that contribute to the Colorado River..................................................................................................................................... 2-10 3.1 Visible spectrum satellite image......................................................................................................3-2 3.2 Weather radar image ...........................................................................................................................3-3 3.3 500 mb map.............................................................................................................................................3-4 3.4 GFS model forecast ...............................................................................................................................3-5 3.5 HYSPLIT plume dispersion forecast...............................................................................................3-6 3.6 Special instrument suite at Brian Head Ski Area.......................................................................3-7 3.7 Close-up photo of the special instrument suite at Brian Head ............................................3-8 3.8 Radiometer sites at the Brian Head Ski Resort....................................................................... 3-10 3.9 Example of radiometer data........................................................................................................... 3-10 4.1 Cumulative and budgeted seeding hoursst for core program .................................................4-1 4.2 Snow water content in Utah on April 1 , 2019..........................................................................4-4 4.3 NRCS SNOTEL precipitation and snow water content plot, Dry Fork ..............................4-5 4.4 NRCS SNOTEL precipitation and snow water content plot, Mammoth Cottonwood .......................................................................................................................4-6 4.5 NRCS SNOTEL precipitation and snow water content plot, Webster Flat ......................4-7 4.6 November 2019 precipitation, percent of normalth................................th ....................................4-9 4.7 Brian Head ice detector site data, November 25 -26 ....................................................... 4-11 ii Table of Contents Continued Figure Page 4.8 December 2019 precipitation, percent of normalth ................................th ................................