Significant progress in the author's ability to distribute point monthly and annual precipitation data to a regular grid in complex terrain has recently been achieved through the development of PRISM (Precipitation-elevation Regressions on Independent Slopes Model). PRISM is well suited to regions with mountainous terrain, because it incorporates a conceptual framework that addresses the spatial scale and pattern of orographic precipitation. In a model comparison, PRISM exhibited superior performance to various methods of kriging in the Willamette River Basin, Oregon and has been applied to the entire United States with excellent results. PRISM was used to develop a new official isohyetal analysis for Oregon -- the first update since 1964. The PRISM-generated map equals or exceeds the accuracy and detail of the hand-drawn 1964 analysis, but required only a small fraction of the time and resources.