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<br />the seeding "model" developed at Climax that was to be applied in the San <br />Juan Mountains. Specifically, when cloud tops were warmer than -290C and the <br />air mass was stratiform, or contained only minor embedded cumulus clouds, <br />precipitation was almost doubled by seeding. This type of cloud would <br />ordinarily produce about ten percent of the total winter season precipita- <br />tion. In clouds of this same type but with tops colder than -290C, seeding <br />apparently resulted in a decrease in precipitation - but this is not sta- <br />tistically significant, and with light winds there were increases in this <br />cold category. Orographic clouds containing deep embedded cumulus clouds <br />showed little difference between seeded and unseeded samples. <br /> <br />The overall potential for seeding-produced increases in precipitation, <br />provided only suitable clouds are seeded, is conservatively about ten per- <br />cent, depending upon location over the barrier. The resultant potential <br />increase in streamflow, calculated by a hydrologic computer model, is about <br />" <br />.J..8' percent. <br /> <br />The full potential of seeding was not realized in this five-year pro- <br />gram because of the randomized seeding and because many clouds actually <br />seeded were not of a suitable type. To a considerable extent this arose from <br />the need to forecast cloud conditions far ahead (up to 24 hours) of the <br />experimental day, a very difficult task subject to large error. The rigors <br />of seeding by 24-hour experimental periods on a randomized basis imposes <br />some problems not found when operations can be altered as the cloud condi- <br />tions change, as occurs in a strictly operational program. There were also <br />instances of mistargeting under certain special wind and air-mass stability <br />conditions. <br /> <br />This five-year test has provided additional information that will lead <br />to better design features in the future. If careful attention is paid to <br />the findings of this report, future winter orographic seeding programs will <br />be more successful in providing technological information on precipitation <br />enhancement methodology as well as increasing water supply. <br /> <br />-20- <br />