WMOD00433

• Title: Generalized Criteria for Seeding Winter Orographic Clouds
• Date: 12/12/1978
• Weather Modification - Doc Type: Report

1770

JOURNAL OF APPLIED METEOROLOGY

VOLUME 1:'

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FIG. 1. Location of the seven projects used in generalized seedability criteria study.

graphical extremes be covered, that randomization of
seeded events was used, and that sufficient quality
data be readily available to permit a reasonable likeli-
hood that statistical significance could be reached
through testing.
The quality and quantity of data varied considerably
from project to project. Rather than narrow the set
of cases to include only those few projects or portions
of projects with the most complete physical measure-
ments, it was decided to base the study on precipitation
gage data and rawinsonde information. Since this in-
formation was available for all the projects the range
of geographic settings (see Fig. 1) and meteorological
conditions covered by the analysis was increased. The
other data that were available from the projects were

TABLE 1. A brief description of the seven 'projects used in this
study_ Listed are the major mountain barrier within the projects'
experimental area, the state where the project was located and the
inclusive dates of winter seasons during which seeding occurred.

Project Size Seeding operations
Bridger Range Project Rocky Mountains- 1969-70 to 1971-72
Montana (3 seasons)
Climax Project Rocky Mountains- 1960-61 to 1969-70
Colorado (10 seasons)
Colorado River Basin
Pilot Project Rocky Mountains- 1970-71 to 1974-75
Colorado (5 seasons)
Central Sierra Research
Experiment Sierra Nevada- 1968-69 to 1972-73
California (5 seasons)
".r emez Mountains Project Rocky Mountains- 1968-69 to 1971-72
New Mexico (4 seasolls)
Pyramid Lake Pilot
Project Sierra N evada- 1972-73 to 1974-75
California/Nevada (3 seasons)
Santa Barbara Project South Coastal 1967-68 to 1973,-74
Range-California (7 seasons)

used to provide insight into the interpretation of results
derived from the statistical analysis.
Seven projects were chosen for this analysis: the
Bridger Range Experiment in Montana (Bridger), the
Climax Experiments in Colorado (Climax), the Colorado
River Basin Pilot Project in Colorado (CRBPP-San
Juan), the Central Sierra Research Experiment in
c:::alifornia (CENSARE), the Jemez Project in New
Mexico (Jemez), the Pyramid Lake Pilot Project in
Nevada (Pyramid Lake), and the Santa Barbara II
Project in California (Santa Barbara). Table 1 lists the
projects, their sites and their period of seeding opera-
tions. Each, of the projects had different topography,
climatology, opportunity recognition criteria, treat-
ment procedures and evaluation techniques.
The basic information used in this study was the
rawinsonde data at 6 h intervals during experimental
events, 6 h precipitation totals summed from 2 h before
the sounding to 4 h after the sounding, descriptions of
the individual mountain barriers and seeding networks,
and tabulations indicating when the seeding generators
were on and off. If at least one generator was on during
the period 1 h before the start of a 6 h block to 1 h before
the end of the block, the period was considered seeded.
Carryover contamination was not considered.
An important part of this study was to identify where
the effects of seeding occurred as well as the magnitude
of the effect. Therefore, the precipitation gages were
grouped in similar regions in relation to the mountain
barrier. The crest group included those gages in the in-.
tended primary target area of the individual projects"
generally those along and on either side of the ridge
crest. Other groups of gages were considered as upwind.
or downwind of the crest group of gages.

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