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<br />Seeding opcrationa were undertaken in tho control area <br />during the month of April, 1951, and hence this method of <br />analysis was possible only for the month of March. The <br />control area was chosen on the basis of correlation studies <br />between stations in the terget and control areas. <br /> <br />" <br /> <br />Snowfall 2ll Target ~ <br /> <br />The effect of seeding on the snow pack in the target <br />area was studied statistically by cor~uting the mean dep~h <br />of water content change of the snow on the target area, <br />using an aritlunetical mean, for the months of March and <br />April, and summation of the two months fur each year from <br />1938 through 1951. Snow-survey information was not avail- <br />able for the month of May. A plot was drawn for each period <br />consisting of mean depth of water .content change versus years <br />and the thirteen-year normal mean depth of water content <br />change. Snow-pack records are based on monthly snow surveys <br />made through April of each year by the Soil Conservation <br />Service and, hence, the amount of snow melt, which depends <br />to a great extent on temperature, between surveys, affects <br />the snow-pack values obtained almost as much as the snowfall <br />itself during the interval. Therefore a study was made <br />showing the relationship of water content change and tempera- <br />ture for the months of Harch and April, and the summation <br />of the two months for each year from 1938 through 1951. <br /> <br />Snowfall on Target Area Versus Control Area <br />- -, <br /> <br />Comparing snow pack on the target area and control area, <br />see Fig. 1, consisted of comparing mean depths of water <br />content change for the periods of March, April, and the <br />summation of the two months for each year from 1938 through <br />1951. <br /> <br />.. <br /> <br />Precipitation on Western United States <br /> <br />Another ~lethod of analYSis used consisted of finding <br />normals for Narch, April, I1ay, and the summation of the three <br />months for stations with precipitation records of forty-five <br />to fifty-five years chosen in the United States west of the <br />Nississippi River. The rainfall of l'Iarch, April, Nay, 1951, <br />and the summation of the three months was computed as a <br />percent of the normal and points of equal percentages above <br />and below normal were connected. The resulting patterns <br />show how the seeded area compares with other sections of <br />western United States in terms of normal precipitation. <br />Correlation studies were ~ade between stations in seeded and <br />non-seeded areas. <br /> <br />,,, ~ <br /> <br />~ <br />V <br /> <br />Precipitation Patterns <br /> <br />One of the advantages of cloud seeding is said to be <br />that it causes the rainfall to be more evenly distributed <br /> <br />3 <br />