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<br /> <br />on percentage of normal snow water content on 10 selected courses <br />distributed over the water shed to approxim~te the sources of water. <br />Average error by .useof one or the other of [the methods since 1948 <br />is 12"/0. ' . <br /> <br />. <br /> <br />Weather Bureau forecasts are based i>n precipitation and stream- <br />flow data. Statistical methods are used for, selection and weighting of <br />index precipitation stations, and determination of monthly weights, <br />September through June. . based on relative! contributions of precipita- <br />tion to yearly runoff. Seasonal precipitatiqn indices thus arrived at <br />are plotted against runoff to determine a grlaphical relation. Nearly <br />40 years of record are used for the Colora~o River Basin. AnApril <br />through July forecast is made by subtractirj.g the recorded October- <br />March flow and the normal August-SeptemQer flow from the water <br />year forecast. The past 6 year average eljror is 8%. <br /> <br />. <br /> <br />.. <br /> <br />iI <br /> <br />. <br /> <br /> <br />. <br /> <br />-30-i <br />