WMOD00400

• Contract/Permit #: 14-06-D-6801
• Title: Structure and Seedability of San Juan Storms
• Date: 11/1/1976
• Weather Modification - Doc Type: Report

I. INTRODUCTION

The Colorado River Basin Pilot Project, or San Juan Project, was a ran-

domized seeding experiment designed to determine if it is feasible to increase

precipitation in the Colorado River Basin by seeding wintertime orographic

storm systems. The experiment was to be a test of the seeding technique, and

if successful could precede seeding of the Colorado River Basin for precipi-

tation enhancement. The experiment ran for five winters, from 1970-71 until

1974-75. The project design is described by Grant et al. (1969). A dis-

cussion of the actual operation program ,,,as presented by Hj ermstad (1975),

and preliminary conclusions from the statistical experiment have been dis-

cussed by Elliott et al. (1975) and by Elliott (1975). Elliott et al. state

that "statistical comparisons of seeded and not seeded experimental day

precipitation show no significant differences at any of the stationslt. As

this conclusion became apparent, the Bureau of Reclamation contracted '(lith

the University of Ivyoming for a detailed study of the microphysical and

dynamical processes in the storms over the San Juan Mountains, which we

conducted during the winter of 1974-75. This report presents our results

from that study. Preliminary results have been reported in Marwitz (1975),

Cooper and Saunders (1975), Marwitz (1976), and Cooper and Saunders (1976).

Earlier aircraft studies in the San Juan.storms were discussed by Marwitz

(1974) and Hobbs et al. (1975). The case study by Marwitz pointed out the

importance of convective clouds, while the study by Hobbs indicated un-

expectedly high ice crystal concentrations in these storms. Hobbs et al.

also studied the transport of AgI from the ground-based seeding generators.

They found that the AgI did not reach cloud level under stable conditions,

and entered the clouds too close to the target area under marginally unstable

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