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<br />16 <br /> <br />ground at a specific time in the form of snow and/or ice which will <br />eventually melt and contribute to the spring runoff. <br />Estimates of annual precipitation have been made using snow course <br />data. A paper by Farnes (1971l outl ined a procedure used to obtain <br />estimates in Montana. He began by developing a simple regression <br />relationship between annual precipitation and April 1 snowpack for <br />locations where year-round raingages and snow courses were co-located. <br />Modifications were then made based on the density of forest canopy in <br />the immediate vicinity of each snow course. A less elegant method was <br />developed as a part of this project using only Colorado precipitation <br />and snowpack data. A two step approach was taken making independent <br />estimates of winter and summer precipitation and combining them to get <br />annual precipitati on. <br />The first step is based on precipitation-snowpack relationships. <br />Snow courses and year-round precipitation gages have been co-located for <br />more than 15 years (within 1 mile horizontal distance and within 200 <br />vertical feet of each other) at 11 locations in the Colorado mountains. <br />From these 11 sites, admittedly a meager sample, a regression <br />re 1 ati onshi p was developed between el evation and the rati 0 of October- <br />April gage precipitation to average April 1 snowpack water content. <br />April 1 measurements were used even though it is prior to the end of the <br />October-April winter season because melting often occurs during April at <br />all but the highest snow courses. <br />The resulting relationship is shown graphically in Figure 5. <br /> <br />16,450 - z <br />R = <br />5,600 <br /> <br />where <br />