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<br />2 <br /> <br />I I. Methoe!ology <br /> <br />The method usee! in deriving the 1931-60 Colorado precipitation maps <br />was fi rst dE vel oped for the state of Utah by the \,ater Supply Forecast <br />Center of the U. S. Weather Bureau in SaH Lake City, Utah. The method, <br />described in a paper by Peck and Brown (1962), was a valid and creative <br />approach to analyzing precipitation patterns in areas of comolex terrain <br />with sparse data Following summarization and adjustnent of <br />precipitation means from available station records (5 to 30 year records <br />for the period 1931-60), regression relationships of precipitation and <br />elevation were developed for various climatic divisions fo" winter and <br />summer seasons. Anomalies from these regression equations W2re defined <br />3S the variati01 of each station mean from the regression line, in <br />inches. These anomalies, found to be related to physiographic features, <br />'~ere plotted on a base map and anomaly isol ines were constructed. These <br />~ere then comnined with the precipitation-elevation relationships for <br />~ach area and for each season to compute mean precipitation values for a <br />Jrid of points on the map leading to the final isohyetal contouring. <br />Rather ~han starting over with a new method or developing new <br />iJrecipitation-elevation relationships and new anomaly contours (which <br />\'Ioul d have been costly and time consuming), the decision was made to <br />dccept the original precipitation map as the starting point for the new <br />a~alysis, changing contours only in areas where substantive evidence now <br />exists to justify modification. Therefore, the emphasis was placed on <br />~inding and incorporating as much new data as possible into this <br />analysis. In oarticular, great effort was made to include high <br />elevation data (> 9,000 feet) to assure accuracy in the highest <br />precipitation zones in Colorado. A study by Loren Crow (1982), which <br />