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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However, Reynolds (1996) showed that ice crystals produced by propane releases too near a crestline may
often be transported downward by mountain lee waves, with resulting sublimation of seeding crystals.

3. RANDOMIZED EXPERIMENTAL DESIGN

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3a. Design Overview

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Scientists and statisticians generally agree that demonstration of winter cloud seeding effectiveness
requires randomization so that snowfall from nonseeded experimental units (hereafter EUs) is monitored
in the same manner as from seeded EUs. All attempts must be made to eliminate human bias in analyses
of any randomized experiment. Statistical evaluation of non-randomized seeding projects has serious
difficulties and uncertainties as discussed by Dennis (1980), Gabriel (2000), Super and Heimbach (2003),
and several other authors.

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A previously used high altitude seeding site (HAS), well up the windward (west-facing) slope of the
north-south oriented Wasatch Plateau of central Utah, was used for 40 min propane releases and paired
nonseeded 40 min placebo periods, the latter to provide a basis of comparison, Figure 1 is a map which
shows the general terrain, instrumented sites and other features. A site on the west edge of the plateau top
was the primary target, referred to as TAR, along with its companion precipitation gauge, GTR. Figure 2

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39'36'O'N

111'21'O'W 111'25'30'IN

1II'19'30'IN

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39'40'30'N

TAR Target Weather Obs,
an d 2 DoC probe
HAS Propane seede...
and Weather Obs,
TSO Icing Obs,
SIR Weather Obs,
GSC Target
GRD Target
GTR Target
GDN Target
GSO Target
GNO Control

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39'39'O"N

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39"31'30'N

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111'27'O'W 1II'25'30'IN

I 11'24'O'W 111'22'30'IN 1II'21'O"W 111'19'30'IN 111'18'O'W 111'16'30'IN 111'15'O'W

IJ... ..w. 1 2 ~i<jlometers
Contour Interval 200 met...

t-:
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,-

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Fig. 1. Map of experimental area for the Utah 2003-2004 propane seeding experiment. The contour interval is
200m.

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