WMOD00299

• Title: Physical Structure of Northern Colorado River Basin Cloud Systems
• Date: 9/1/1985
• State: CO
• Weather Modification - Doc Type: Report

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17

some experiments, particularly with aircraft seeding, high reflectivity

regions associated with AgI plumes were identified.

Super et ale (1972) also provided a radar derived cloud top

climatology for the region based on one winter season which indicated

that mean precipitation tops were at 14400 ft M.S.L. Precipitation tops

exceeded 16000 ft M.S.L. in only 7~ of the cases. Tracking radar

studies of airflow over the Bridger Range based on pibal releases

indicated that air approaching the barrier accelerated significantly

near the crest, particularly at low levels.

During the 1971-72 season, several days were set aside for physical

experiments designed to directly detect the effects of cloud seeding.

Twelve case studies developed from these experiments were reported by

Super et al., (1972). In many cases, changes in the precipitation

characteristics observed were attributed to seeding. However, these

studies provided little information concerning natural cloud system

structure since all were seeded events.

(S) The Colorado River Basin Pilot Pr01ect

The Colorado River Basin Pilot Project was conducted in the San

Juan Mountains of southwest Colorado during the five winter seasons

ending in 1974-75 (Elliott et al.. 1978). Physical studies of cloud

systems occurring over the San Juan Massif during this period were

conducted by the University of Wyoming (Marwitz (1980); Cooper and

Saunders (1980); Cooper and Marwitz (1980)) and the University of

Washington (Hobbs et al., 1975a). Results of these studies indicate

that most storms in the San Juans evolve through four stages related to

thermodynamic instability. These were a stable stage, followed by

neutral, unstable and dissipation stages.