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<br />4 <br /> <br />II!. Data <br /> <br />A 30-year avera'ling period, 1951~1980, was chosen for the new <br />analysis to coincide with the most recent standard period for computing <br />"normals" used by the National Cl imatic Data Center. Hater years <br />(October I-September 30) were used for calculation of annual <br />precipitation totals. In Colorado, this is more practical than the <br />calendar year since it is well correlated with the state's water <br />storage/water usage cycle. Mountain snows begin accumulating in October <br />and this snoV/pack normally continues to build until sometime in April <br />and May. Peak water usage is associated with the May-September growing <br />season since agriculture accounts for the vast majority of watel^ used in <br />Colorado. Der~and peaks during early and mid summer and then tapers off <br />in September as temperatures cool and crops mature. Over a 3D-year <br />0eriod, the choice of which 12-month period is used to calculate annual <br />precipitation totals and averages has very little effect on the final <br />results. <br />The first step towards the completion of a new Colorado <br />precipitation map was thorough investigation of available data sources. <br />Major emphasis was placed on obtaining data from networks consisting of <br />several stations employing consistent instru~entation and observing <br />techniques. In Colorado, this implied that the vast majority of the <br />precipitation data meeting the requirements of this map analysis came <br />from Federal sources. <br />A mi nifl1um of 15 years of consistent data (data from one site or a <br />compatible ;learby location(s)) from the 1951-1980 period was a <br />requirement for a station in order to be included in the analysis. <br />Adjustment techniques described in Section IV were used to fill in <br />