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.~ 2 II. Methodology The method used in deriving the 1931-60 Colorado precipitation maps was first developed for the state of Utah by the Water Supply Forecast Center of the U. S. Weather Bureau in Salt Lake City, Utah. The method, described in a paper by Peck and Brown (1962), was a valid and creative approach to analyzing precipitation patterns in areas of complex terrain with sparse data. Following summarization and adjustment of precipitation means from available station records (5 to 30 year records for the period 1931-60), regression relationships of precipitation and elevation were developed for various climatic divisions for winter and summer seasons. Anomalies from these regression equations were defined as the variation of each station mean from the regression line; in inches. These anomalies, found to be related to physiographic features, were plotted on a base map and anomaly isolines were constructed. These were then combined with the precipitation-elevation relationships for each area and for each season to compute mean precipitation values for a grid of points on the map leading to the final isohyetal contouring. Rather than starting over with a new method or developing new precipitation-elevation relationships and new anomaly contours (which would have been costly and time consuming), the decision was made to accept the original precipitation map as the starting point for the new analysis, changing contours only in areas where substantive evidence now exists to justify modification. Therefore, the emphasis was placed on finding and incorporating as much new data as possible into this analysis. In particular, great effort was made to include high elevation data (~ 9,000 feet) to assure accuracy in the highest precipitation zones in Colorado. A study by Loren Crow (1982), which , .