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<br />., <br /> <br />, <br /> <br />e <br /> <br />e <br /> <br />e <br /> <br />211 <br /> <br />Monitoring <br /> <br />Each pennit lists special circumstances under which the project must be suspended automatically. <br />The suspension criteria are intended to help limit the potential hannful impact of too much snow on <br />the local economy and the hazard from too much snow being the cause of avalanches or spring <br />floods. Some of the potential local impacts considered. in the past have included the extra costs of <br />snow removal, traffic congestion and loss of retail trade, livestock feeding patterns, disruptions to the <br />calving season, and changes in the planting of crops. <br /> <br />Operators are required to suspend seeding operations if at any time the average of the. snow pack <br />accumulations, measured in equivalent inches of water at Snotel sites selected to represent the target <br />area, exceed certain percentages of the average snow pack for the 30-year base period from 1961 to <br />1990. For example, snow pack accumulations might be limited to 175% of average on January 1 st, <br />160% of average on February 1 st, 150% of average on March 1 .t, and 140% of average on AprilI'l. <br />Snow pack accumulation is monitored at least weekly from snow survey measurements conducted by <br />the Natural Resources Conservation Service, U.S. Department of Agriculture. <br /> <br />Effectiveness <br /> <br />The effectiveness of weather modification is difficult to measure. It usually involves a comparison of <br />results in the target area to precipitation in a "control" area. However, a 10- to I5-percent increase in <br />snow pack from ground based winter generators is typical. The theoretical limit under ideal <br />circumstances is a 25% increase. Assuming a 10 % effectiveness, only a very small fraction (0.2% to <br />0.3%) oftbe available moisture in the atmosphere is removed as a new source of water supplies. <br /> <br />Ground based winter cloud seeding projects in Colorado have been estimated to have average yields <br />of 30 to 50 acre-feet per square mile at unit costs varying from less than $1 to $7 per acre-foot. An <br />average savings of$4 million per year from reduced crop damages from hail has been reported in <br />westemKansas with a benefit to cost ratio as high as 37 to 1. Although some scientists think hail <br />cannons are a hoax, most owners can remember times during a hail stonn when their crop was <br />protected and their neighbors' were not. <br /> <br />Conclusion <br /> <br />This agenda item is for infonnational purposes. Mr. Larry Hjermstad, Manager for Westem Weather <br />Consultants, LLC, of Durango, who holds pennits for 3 of the 5 ground based winter weather <br />modification projects, and myself are planning to be at the meeting to make a presentation and <br />answer your questions. In the meantime, you might find the attached publication entitled "What is <br />Weather Modification? - Answers to the 21 most asked questions about cloud seeding in Colorado" <br />of interest. You will also find a section on the CWCB web page (http://www.cwcb.state.co.us) <br />devoted to weather modification. <br /> <br />Enclosures: <br /> <br />Table of Active Weather Modification Permits <br />Map of Weather Modification Target Areas <br />What is Weather Modification? <br /> <br />Agenda Item 12 032601 - WMPP Briefing <br /> <br />3 <br />