Description
Overview
The Wyoming Water Development Commission, on behalf of the State of Wyoming, is overseeing the conduct of the Wyoming Weather Modification Pilot Projects, a winter cloud seeding program to increase snowpack and runoff within Wyoming's Green River, Wind River, and Platte River basins. This program involves cloud seeding operations, to be implemented by Weather Modification, Incorporated (WMI) based in Fargo, North Dakota, and scientific evaluations, performed by the National Center for Atmospheric Research (NCAR) Research Applications Laboratory (RAL).
Cloud seeding technology will be used and evaluated in the pilot program as a long-term water management tool rather than as a tool to mitigate the effects of drought conditions. Cloud seeding is most effective under normal or near-normal weather conditions. However, the benefits during dry years cannot be ignored.
The Wyoming weather modification program will use cloud seeding in two regions in an attempt to increase precipitation (snowpack) over targeted mountainous areas by up to 10 - 20 % per year; amounts well within the range of natural variability between winter seasons and for individual storms. The two proposed pilot cloud seeding regions are located in two diverse and widely separated areas, the Medicine Bow/Sierra Madre Mountains and the Wind River Range of Wyoming.
Ground-based and airborne cloud seeding efforts using a silver iodide-based seeding agent are planned for each region over a period of 4.5 months (Nov. 15 - Mar 31) and over five successive winter seasons. The pilot program will continue for a period of five years because natural variability is high and five years should allow the technology to be demonstrated over a range of winter conditions. Intense storm systems that are forecast to produce heavy snows will generally not be seeded, because these storms have been shown to be naturally efficient in producing precipitation. Under average conditions, seeding may be feasible six to ten times per month in each target area. Seeding in each event may vary from an hour to many hours, depending on the persistence of suitable clouds. Monitoring and evaluation of the pilot program will continue throughout the 5-year pilot program and will culminate in a final report.
Medicine Bow/Sierra Madre Pilot Project
The proposed Medicine Bow/Sierra Madre Pilot Project region in southeastern
Wyoming will include portions of Carbon and Albany Counties. The pilot program
will have at least one evaluation target area per mountain range and may target
specific areas within the Medicine Bow National Forest for increased snowpack.
Wind River Pilot Project
The proposed Wind River Pilot Project region in west central Wyoming includes portions of Sublette and Fremont Counties. The pilot program will target specific areas on National Forest administered lands within the Wind River Range for increase snowpack. It will be designed in collaboration with, and will be compatible with, the ongoing cloud seeding program of the Eden Valley Irrigation District (EVID), which uses three silver iodide generators along U.S. Highway 191 north of Farson, and two high-altitude propane generators located on Muddy Ridge to the east and operated by the Bureau of Reclamation.
Operations
Operational and suspension criteria, best management practices, and a monitoring and evaluation plan are under development for the pilot program. WWDC, WMI, and NCAR anticipate that the involvement and guidance of the technical advisory team will be needed to complete development of these program design criteria. When completed, WWDC, WMI, and NCAR anticipate inclusion of the aforementioned criteria and practices and any other applicable program design criteria as part of the proposed action that will be analyzed under the National Environmental Policy Act (NEPA).
Ground-based efforts will involve the development of roughly three to seven small generator sites, located at intervals approximately 12 to 20 km upwind of the central portion of each evaluation target area. Local topography (valleys, draws, ridges, etc.) and upslope wind conditions will be considered when identifying the siting zones. The pilot program budgeted for 24 generator sites total for both target regions. NCAR is currently evaluating the sites under consideration for generator placement. The proposed sites will be finalized based on NCAR's evaluation and feedback received from affected agencies regarding resource concerns.
Generators will be remotely controlled and will use the latest technology for sustainability (solar and wind power). They will generally be sited in locations accessible by helicopter or snowmobile during winter, outside crucial big game winter ranges and away from sage grouse leks. Although maintenance and repairs for generators are anticipated to be infrequent, some type of access to the generator sites during winter will be needed occasionally, and most roads located on National Forests and public lands become impassable during winter.
A generator and related equipment needed for the release of the silver iodide-based seeding agent will be placed at each site. Each generator site will require a level area 10 feet by 10 feet. The equipment at each site will include a 10-20 foot tower so that the seeding agent will catch the wind. At four sites, additional weather instruments will be deployed requiring a second tower.
During ground-based cloud seeding operations when cloud conditions are right, a solution of silver iodide (AgI) will be burned in a propane flame, producing a large number of small ice nuclei (i.e., seeds for ice crystals) that will be caught up into the wind. Generator outputs can be varied, but at least initially should be 30 g AgI consumed per hour. The anticipated chemical composition (including minor components), concentration, volumes, and mean particle size of the seeding agent being released will be specified in the final operations plan so that effects on air quality related values and visibility can be analyzed under NEPA.
Ground-based operations will affect private lands, State of Wyoming lands, the Wind River Indian Reservation (WRR), and lands administered by the Bureau of Land Management (BLM) and the U.S. Forest Service (USFS). It is anticipated that extended areas roughly 25 to 100 miles downwind of the targeted areas potentially will be affected by very small increases in precipitation.
Evaluation
Snow samples will be taken at intervals for a limited number of storms in the evaluation target area for silver analysis to verify targeting. Instrumentation for detailed monitoring and evaluation of the effects of cloud seeding have already been deployed (i.e. SNOTEL sites) but additional instruments may be deployed in one or two of the evaluation areas for better coverage of snowfall events. Portable equipment and instruments, either temporarily deployed or housed on a small trailer, will be used at specified locations. One example is the deployment of a microwave radiometer, which passively measures atmospheric water vapor, liquid water in clouds, and with inversion techniques, temperature profiles. A companion study of snowfall rates may be implemented in the areas of interest to improve prediction of snow water equivalent and runoff potential, and to better understand the relationship between measured surface snowfall rates and radar reflectivity values. Collaborative efforts between glacier research studies in the Wind River Range and measurements taken during these pilot programs (e.g., snow and snowfall rates) will also be pursued.
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