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Cloud Seeding Annual Report

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Cloud Seeding Annual Report Cloud Seeding Annual Report Six Creeks Program 2019-2020 Winter Season Prepared For: Salt Lake City Department of Public Utilities Prepared By: Todd R. Flanagan Garrett Cammans North American Weather Consultants, Inc. 8180 South Highland Dr. Suite B-2 Sandy, UT 84093 Report No. WM 20-13 Project No. 19-443 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 EXECUTIVE SUMMARY ...................................................................................................................................... iii 1.0 INTRODUCTION........................................................................................................................................ 1 2.0 CLOUD SEEDING THEORY .................................................................................................................... 3 3.0 PROJECT DESIGN ..................................................................................................................................... 5 3.1 Background ............................................................................................................................................ 5 3.2 Seedability Criteria ............................................................................................................................. 5 3.3 Equipment and Project Set-Up ....................................................................................................... 6 4.0 WEATHER DATA AND MODELS USED IN SEEDING OPERATIONS ...................................... 9 5.0 OPERATIONS .......................................................................................................................................... 15 5.1 Operational Procedures ................................................................................................................. 22 5.2 Operational Summary ..................................................................................................................... 23 6.0 ASSESSMENT OF SEEDING EFFECTS ............................................................................................ 36 6.1 Background ......................................................................................................................................... 36 6.2 Evaluation Approach ....................................................................................................................... 37 6.3 Target and Control Data Resulting Equations ....................................................................... 38 6.4 Results for the 2020 Water Year ................................................................................................ 43 References Figure Page E.1 Utah Percent of Median April 1, 2020 Snow Water Content ................................................... iv 1.1 Six Creeks Target Area............................................................................................................................. 2 3.1 Target Area and Seeding Site Locations ........................................................................................... 7 3.2 White Reservoir Cloud Seeding Site ................................................................................................... 8 4.1 Visible Satellite Image at 1746 MDT on March 24, 2020 .........................................................10 4.2 Composite Reflectivity radar image at 1545 MDT on March 24, 2020 ..............................11 4.3 700 mb map valid at 0600 MDT on March 24, 2020 ................................................................. 12 4.4 HYSPLIT one-hour plume dispersion forecast for March 24, 2020 .....................................13 4.5 GFS Model Forecast for March 23, 2020 .........................................................................................14 5.1 NRCS SNOTEL plot for Louis Meadow .............................................................................................20 5.2 NRCS SNOTEL plot for Mill D - North...............................................................................................21 5.3 NRCS SNOTEL plot for Snowbird ......................................................................................................21 5.4 Cottonwood Creeks Snow Water Equivalent values 2018-2020 ..........................................22 5.5 January 1, 2020 SWE Percent of Normal for all Utah Basins ..................................................25 5.6 February 1, 2020 SWE Percent of Normal for all Utah Basins ...............................................28 5.7 March 1, 20202 SWE Percent of Normal for all Utah Basins ..................................................30 i Table of Contents Continued Figure Page 5.8 April 1, 2020 SWE Percent of Normal for all Utah Basins .......................................................33 5.9 April 17, 2020 SWE Percent of Normal for all Utah Basins .....................................................35 6.1 Six Creeks SNOTEL Target Site Locations ......................................................................................40 6.2 Six Creeks SNOTEL Control Site Locations ....................................................................................41 Table Page 3-1 Seeding Site Locations............................................................................................................................. 7 5-1 Storm Dates and Generator Usage – 2019-2020 Winter Season ..........................................16 5-2a Generator Hours for 2019-2020, Storms 1-12 ............................................................................17 5-2b Generator Hours for 2019-2020, Storms 13-24 .........................................................................18 5-3 Snowpack and Precipitation Data – April 17, 2020 ...................................................................19 6-1 Target and Control SNOTEL Sites for Precipitation and Snowpack Evaluations ...........42 6-2 Regression Equations ............................................................................................................................43 6-3 Evaluation Results for the 2020 Water Year ................................................................................45 ii EXECUTIVE SUMMARY Salt Lake City initially sponsored winter cloud seeding programs targeting the Six Creeks drainage basin in Water Years 1989 through 1996, with NAWC operating these programs. NAWC analysis of potential effects of the seeding indicated positive effects (~6% to 17% for water years 1989 and 1990, Thompson, et al., 1990). It was NAWC’s understanding that this program was discontinued following water year (1996) due to budgetary considerations. SLCDPU expressed an interest in the fall of 2018 in re-establishing a cloud seeding program to impact the Six Creeks drainage basins that provide runoff to the Salt Lake Valley. A proposal was drawn up by NAWC and accepted by SLCDPU in the fall of 2018, and the first season of operations for the current program began in December 2019. NAWC submitted another proposal in early October 2019 for a second season of cloud seeding for Six Creeks, and it was accepted a few weeks later. This season’s cloud seeding program began on November 15, 2019 and ended on April 16, 2020. A total of 24 storm events were seeded during all or portions of 38 days during the 2019-2020 season, using a network of eight ground-based silver iodide generators. Two of these events occurred in November, two in December, nine in January, three in February, six in March and two additional seeding events in April. A total of 838.00 cumulative hours of seeding generator operations were conducted during the season from the ground sites. Figure E.1 shows the April 1 NRCS snowpack basin percentage of median map for the state of Utah. Snowpack/precipitation was near to slightly above normal in the Six Creeks project area during the 2019-2020 winter season. As of April 17, 2020, sites in the Six Creeks target area reported snowpack water content ranging from about 95% to 143% of the median, with an overall basin value of 108%. iii Figure E.1 Utah Percent of Median April 1, 2020 Snow Water Content Target/control evaluations were developed for the Six Creeks seeding program, utilizing NRCS SNOpack TELemetry (SNOTEL) precipitation and snow water content data. The precipitation evaluations include those utilizing both December – March and November – April iv totals. For this report,
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