WMOD00412

• Title: Final Report on Utah Cloud Seeding Experimentation Using Propane During the 2003/04 Winter
• Date: 3/1/2005
• State: UT
• Weather Modification - Doc Type: Report

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is a vertical cross section whose plane runs through HAS and GTR. Considerable previous plume
tracking had shown that plumes released from the seeding site routinely passed the TAR vicinity when
winds there were from the southwest quadrant. Pairs of EUs, one seeded and one not treated by random
decision, were declared whenever an icing rate sensor at the HAS seeding site detected the presence of
SL W above a threshold. It is well documented that SL W availability is the necessary "raw material" for
winter cloud seeding in mountains to be effective. Randomized seeding and all observations were totally
automated providing 24/7 operations to maximum the population of EUs.

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3000 -
MeIers

- 3000

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Fairview (1829)

Wasatch Plateau

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,Sanpete Valley

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Sea . '

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K1klmelers

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Vertical:Horizontalscale = 3:1

Fig. 2. Vertical cross section through HAS and GTR showing relative locations of instrumented sites,

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Primary measurements for statistical evaluation of seeding effectiveness were from high resolution
precipitation gauges manufactured by ETI Instrument System, Inc. Gauges were equipped with Alter
windshields and were located in natural clearings in conifer (evergreen) forest to minimize wind-caused
undercatch of snowfall. The snow melted in an antifreeze solution within each gauge and resulting
weight changes were measured by a sensitive load cell. A Campbell data logger within the gauge housing
recorded the average weight for each minute. Each gauge was individually calibrated and its coefficients
were incorporated into the data logger program. The highly sensitive gauges proved to be very reliable,
resulting in no missing data for any EU period at any gauge. Data from gauge data loggers were
downloaded into a Palm Pilot device during approximately weekly visits. A running mean of five was
fitted to aliI min gauge samples, centered on the middle minute, before calculations ofSWE
accumulations. Examination of resulting smooth time history plots suggests that gauge resolution was
between 0.002 and 0.003 inch. While scientific papers usually report precipitation in metric units, the

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