WMOD00272

• Title: The Feasibility of Operational Cloud Seeding in the North Platte River Basin Headwaters to Increase Mountain Snowfall
• Prepared For: US Department of the Interior Bureau of Reclaimation
• Prepared By: Jonnie G. Medina, Technical Service Center, Water Resources Services
• Date: 5/1/2000
• County: Statewide
• State: CO
• Weather Modification - Doc Type: Scientific Study

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The long-term winter cloud seeding projects known as Climax I and Climax II (intended as a replication
of Climax I) were conducted in the Climax, Colorado area in the 1960s. Little of to day's sophisticated
sensing equipment existed then so the projects were largely statistical estimation of seeding effects.
These projects (Mielke et aI., 1970, 1971; Mielke et aI., 1981) have been embroiled in controversy
(Rangno and Hobbs, 1993; Rangno and Hobbs, 1995; Mielke, 1995; Gabriel, 1995). Mielke (1995). The
lead statistician that analyzed results recently reiterated that he stands by his evaluation of precipitation
increases of26 percent for the combined project data. The appeal of the results for Climax I and II lie in
the project replication and the overall lengthy study period lasting a decade. The shortcomings lie in the
lack of physical measurements accompanying seeding trials. The Bridger and Climax results point to
about a 25 percent increase in the seeded sample over the control sample. This estimated precipitation
increase amount is used here in calculations to estimate possible increases in the water volume deposited
in targeted areas of high elevations ofthe Headwaters Region.

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2.2. Cloud Seeding Basics

The proposed project will deal with the modification of winter clouds that largely exhibit orographic
cloud structure. A schematic of an orographic cloud is given in figure 2.1. These clouds often form in
the Headwaters Region and consist of SL W droplets in amounts estimated to be suitable for seeding.

Distance (km)
-32 -24 -16 -8 0 8
20000

WIND~

16 24 32
6.0
5.5
5.0
4.5 ..-...
E
4.0 ::I-
-'
C
3.5 0
:0:
0
>
3.0 Q)
.....

c
o
+=
o
~ 10000
W

2.0

-=- 15000
Q)
Q)
-
......

5000
-20 -15 -10 -5 0 5 10
Distance (miles)

15

1.5
20

Figure 2.1. - Conceptual model of orographic cloud with SL W zone
and AgI seeding plume (adapted from Super et al, 1993).

Typically, liquid cloud droplets form as moist air cools and rises over the windward slope of a mountain
barrier. The SLW droplets rapidly evaporate in descending (warming) air over the lee slope as shown in
the cloud schematic. The purpose of cloud seeding is to convert the water droplets to snow particles that
can grow enough to reach the mountain surface as snowfall before they evaporate/sublimate (see
appendix A, chapter 3, for a more thorough description of this process). Snow particles must have
enough growth time in a favorable environment to achieve mass sizes that allow descent to the ground,

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