WMOD00284

• Applicant: Thompson, J.R., G.W. Wilderson, and D.A. Griffith, North American Weather Consultants
• Sponsor Name: USBR
• Title: Cloud Seeding Data Collection, and Analysis Assoc. with the Colo River Augmentation Demonstration Program
• Prepared For: USBR, Divison of Atmospheric Research
• Prepared By: Thompson, Wilderson, Griffith
• Date: 12/1/1987
• State: AZ
• Weather Modification - Doc Type: Scientific Study

for the A-2 storm types precipitation averaged only about
half that much (43 percent of the hours).

Precipitation generally began a few hours after the onset
of SLW at Happy Jack, usually when a major synoptic feature
was still many miles upwind. This distance averaged 170 nautical
miles to the west or northwest (median 200 nautical miles)
with the greatest distance 250 miles. However, in several
episodes precipitation did not begin until a front (or trough)
was passing or had passed the Happy Jack area.

It would appear the best seeding technique would be to
commence seeding when SLW was indicated to be in abundance
(preferably in the moderate to strong range). From the above
findings, in the absence of a microwave radiometer with real-time
readings of SLW, an acceptable seeding strategy could be to
begin seeding when precipitation was observed to be starting
over the region and/or when a synoptic feature was indicated
to be within 200-250 nautical miles of the area. Provided
other factors, such as the presence of predominantly cold
ice clouds or predominantly warm (not supercooled) water clouds,
did not indicate that SLW might not be present, such a technique
should be effective in the majority of the cases.

From experience gained during the field season in watching
the development of the storm systems as they approached Arizona,
it is concluded that forecasting the timing of the onset of
SLW and/or precipitation more than a few hours (10 or less)
before it is observed would be difficult in most cases. There
were some synoptic storms that developed and/or moved in a
completely predictable manner but they seemed to be the exception
and with the majority of the storms it was a case of watch

3-19

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