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<br />Correlations of monthly and annual mean precipitation between every <br />combination of pairs of the 30 stations were computed. The best interstation <br />correlation coefficient for the monthly data was 0.85. About 3 percent of <br />those correlations was greater than 0.80, 17 percent was greater than 0.70, <br />and 30 percent was greater than 0.60. The highest interstation correlation <br />for the annual values was 0.84. Less than 1 percent of those correlations was <br />greater than 0.80; 11 percent was greater than 0.70; and 18 percent was <br />greater than 0.60. Selected classes of interstation correlation of monthly <br />precipitation for every pair of stations is presented in the tables in the <br />"Supplemental Information" section at the end of the report. Correlation of <br />monthly and annual mean pTecipita~ion be~~een s~a~ions seemed to be related to <br />geographical distance. In general, the closer the stations, the higher their <br />interstation correlation. However, the stations are too far apart to develop <br />useful distance-correlation relations. <br /> <br />A statistical test (Kendall Tau) was computed for each of the 30 stations <br />to identify possible time trends in the annual precipitation. The test indi- <br />cated that two stations, 8064 (Sugarloaf Reservoir lESE) and 8931 (Westcliffe) <br />had downward trends statistically different from zero at the I-percent signif- <br />icance level. The data for station 8931 (fig. 31) are suspect, although the <br />station history gives no evidence to support such claim. The hydrograph for <br />station 8064 (fig. 26) does seem to indicate a trend. Two factors can be <br />cited to discount any real trend: (I) The record length is one of the short- <br />est; and (2) the unfortunate timing of missing records around 1970, especially <br />1969, when nearby stations had above-average precipitation. <br /> <br />Snowpack <br /> <br />The moisture content in snowfall is included in recorded precipitation <br />data. Snowpack, however, represents the accumulation of snowfall minus losses <br />from melting and evaporation. Snowpack, as used in this report, measures the <br />amount of water being held in storage as snow for potential runoff. Snow- <br />survey courses, where snowpack data have been collected, were selected based <br />on length of record and geographic location. The 18 snow-survey courses <br />chosen are shown on plate 1 and listed in table 3. The period of record and <br />mean April 1 snowpack at each site are shown in table 4. Hydrographs of the <br />April 1 measurements of snowpack for these 18 stations are shown in figures 34 <br />to 51. Tables of all the monthly measurements are presented in the "Supple- <br />mental Information" section (tables 43-60) at the end of the report. <br /> <br />Similar to the precipitation data for the mountainous areas, snowpack is <br />dominated by orographic effects. A plot of the elevation and mean April 1 <br />snowpack for the 18 snow-survey courses is shown in figure 52. Although <br />considerable scatter occurs about the regression line (some of which might be <br />explained by geographic location), and although different periods of record <br />are used to compute the means, the regression analysis indicates that, in <br />general, the mean April 1 snowpack increases one-half in. for every 100-ft <br />increase in elevation. Though not shown in figure 52, the intercept of the <br />regression line occurs at about 8,140 ft. This would be the lowest elevation, <br />on the average, at which one would expect snow accumulation on April 1. <br /> <br />24 <br />