WMOD00395

• Title: Weather Modification Reporting Program - 1973-1978
• Date: 6/1/1979
• Weather Modification - Doc Type: Report

Local community sponsorship of weather modifi.cation activities dropped
sharply in CY 1978. Municipal water or conservation district sponsorship
is slowly decreasing, but State sponsorship is increasing sharply. Public
utility sponsors are few and show no drastic changes. There is no appaY4::!nt
trend in the number of Federally sponsored projects during the 6 years.

Target Areas and Locations

The number of States with weather modification activities peaked in CY 1975.
Several projects covered adjoining States, for example, California and Nevada.
A review of the reported target locations clearly shows that the States '\Test
of the Mississippi River have most of the yearly activities. In the eastern
part of the United States, Illinois, Michigan, Delaware, 'and Georgia have had
operational weather modification projects.

The total target area for activities in the United States has increased
each year, even allowing for the anomalous peak of CY 1977. Although thE~
total target area ranges from 3 to 8 percent of the area of the United
States, at no time during any year are all activities underway at the sm~e
time. Thus. on any one ,day, the total target area would be quite small.
There is good indication that the average target area for nonfog '8ctivitie,s
exhibits a general upward trend over the years. The average area for CY
1973-75 is 43 percent more than the average for CY 1976-78.

Duration of Modification Activities

The total number of days on which weather modification was attempted ,varied
from year to year as did the number of days devoted to attempts to increase
precipitation. Fog modification days for ,each year also showed no specific
trend. '

The hours during which fog or cloud seeding was carried out from aircraft
indicated no certain trend over the reporting period. However, the hours of
ground-based operation showed a definite increasing trend.

Seeding Agents

The use of dry ice (C02) to increase airport visibility in periods of
supercooled fog, to create clearings in stratus clouds, or to increase
precipitation in other cloud formations generally was greater until CY 1978
when usage dropped sharply. The peak year for seeding with silver iodide
was 1975. The Air Force relied on liquid propane vented to the atmosphere
in order to alleviate supercooled fog at two of its airports in the UnitE!d
States; however, no obvious trend was observed in the data. The peak year
for using po1yelectrolytes to dissipate warm fog was 1975; during 1978,
this chemical compound was not reported for any activity.

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