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<br />of "freezing nuclei" around which ice crystals <br />originate. Cloud water droplets around regular <br />"cond.ensation nuclei" tend to remain liquid at <br />temperatures warmer than about -40oF! The silver- <br />iodide crystals released into clouds in the South <br />Dakota program help relieve nature's deficit of <br />"freezing nuclei." <br /> <br />The rate at which the rain drop or ice particle grows is <br />largely dependent upon the conditions which exist within <br />a given cloud. If the cloud is vigorously growing it <br />will usually be quite thick and will have rather strong <br />updrafts which continuously supply moist air and conden- <br />sation nuclei to the cloud. <br /> <br />These are the conditions which produce the most precipita- <br />tion. The more active cloud will produce more rain drops <br />and bigger rain drops than the thinner less active cloud. <br /> <br />32 <br />