WMOD00458

• Project Name: Project Skywater
• Title: Generalized Criteria for Seeding Winter Orographic Clouds
• Date: 7/1/1977
• Weather Modification - Doc Type: Report

Project Skywater of the Bureau of Reclamation is currently con-

ducting an a posteriori analysis of seven randomized winter,. oro-

graphic seeding projects conducted in the Western United States.

The analysis is identifying physically definable, generalized seed-

ability criteria for varying meteorological and topographical con-

ditions. The study is considering 11 variables derived from data

from the 7 projects that are measures of (1) the time available

for nucleation, growth, and fallout of precipitation, (2) the amount

of atmospheric water available for conversion into precipitation,

(3) the natural ice nuclei available to form precipitation embryos,

and (4) the atmospheric mixing available to distribute seeding

materials throughout the cloud. It is not possible to accommodate

fully operational differences between the seven projects. The

analysis procedures employed do, however, permit treatment of the

meteorological and topographical differences. Generalized seed-

ability criteria have been derived by integrating the analytical

results into a single set that fits all seven projects.

The impetus for the Bureau of Reclamation to make this search for
generalized seedability criteria comes from two major considerations.
First, the randomized projects conducted over the past 25 years have
included a wide variety of factors considered to be important in

carrying out effective seeding. It is important that these factors

or criteria be sorted and commonalities identified to optimize

3