WMOD00544

• Project Name: Project Skywater
• Title: Project Skywater - An Introduction to Rivers in the Sky
• Date: 12/1/1973
• Weather Modification - Doc Type: Report

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THIS NEW KNOWLEDGE is being con-
verted and expanded into a usable, com-
prehensive technology. In turn, the
technology is being tested and improved.
This ulearn while doing" approach identi-
fies necessary research. At the same time,
additional much-needed water is made
available as a byproduct of the research.

The effect of cloud seeding depends on the
natural efficiency of the precipitation proc-
esses at work within a' cloud. Particular
seeding agents, introduced to critical
areas of a cloud under specific conditions,
can make the precipitation process more
efficient and produce more moisture than
would have occurred if the cloud had not
been treated. It also has been established
that the addition of seeding agents in some
clouds, under some conditions, inhibits
their ability to produce rain, snow, or hail.
Management may thus extend to the de-
crease of precipitation when desired, as
well as an increase.

At this point in the research program, it
appears that summer rainfall in the Plains
States can be increased by 15 to 20 per-
cent through a responsible application of
the current technology. Seasonal snowfall
increases of up to 20 percent can be ex-
pected in winter orographic situations.

One of the major thrusts of Skywater's
current research is to develop means of
identifying these specific conditions; to
develop methods of recognizing seeding
opportunities.

Experiments in this direction are defining
a useeding window" of cloud-top tempera-
tures in which seeding produces an in-
crease- in precipitation. if all other factors
are compatible, and if cloud-top tempera-
tures are approximately between _100 C

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and -230 C, the cloud has been found to
respond positively to silver iodide seeding.
If cloud-top temperatures are colder,
seeding often causes decreases in precipi-
tation. If temperatures are warmer, a dif-
ferent seeding technique may be required.

Temperature, however, is only one of the
many variables. Others include geographic
location, humidity, the number and size of
ice particles present, wind speed and direc-
tion, and updraft velocity. Defining the
role of each ot' these, and several other
factors, in determining the seeding win-
dow is a continuing task.

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COMPUTER-DRAFTED :
CLOUD MODEL

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THE MANY PHYSICAL influences at
work in the atmosphere, or in an individual
cloud, can be simulated only through vast
mathematical equations that represent
these processes. The end result is a com-
puter-drafted cloud model; a numerical
image of a cloud that portrays its charac-
teristics and can predict the behavior or
response of a cloud to varying stimuli-
such as seeding agents. However, only
during recent years has enough been
learned to create even a rough mathemat-
ical cloud model. As each seeding window
criterion is defined, it is integrated into
the model, which, in turn, can more accu-
rately reflect cloud behavior.

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The USBR Steady State Convection Model
is a numerical model of the convective
process found in cumulus clouds. The
computations predict the seedability of
clouds from information on temperature,
humidity~ updraft speeds and other data.
This example of the visual printout is
based on an atmospheric sounding at
Amarillo, Texas, on the morning of Sep-
tember 5, 1973. It predicts that a cloud
with a radius of 1 kilometer (left.column)
will have the potential of producing .204