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PROBABLE MAXIMUM PRECIPITATION ESTIMATES, COLORADO RIVER AND GREAT BASIN DRAINAGES E. Marshall Hansen, Francis K. Schwarz, and John T. Riedel Hydrometeorological Branch Office of Hydrology NOAA, National Weather Service, Silver Spring, Md. ABSTRACT. This study gives general-storm probable maximum precipitation (PMP) estimates for durations between 6 and 72 hours and for area sizes between 10 and 5,000 mi2 (26 and 12,950 km2), for any location in the Colorado River and Great Basin drainages. Total PMP is determined as the sum of convergence and orographic PMP components. Esti- mates are given for each month. The study also provides estimates for local-storm PMP. In addition to the above drainages these estimates are provided for all of California. The estimates cover durations between 15 minutes and 6 hours and drainage areas between 1 and 500 mi2 (2.6 and 1,295 km2). Local- storm PMP is applicable to the warm season between May and October. Comparisons are given between PMP estimates and the greatest observed rainfalls of record, 100-yr fre- quency rainfall and statistically derived PMP. A step- by-step outline of the procedure for computing PMP estimates is presented with examples for both the general and local storm. 1. INTRODUCTION 1.1 Purpose of Report The purpose of this report is to present the material necessary to compute estimates of probable maximum precipitation for any watershed up to 5,000 mi2 (12,950 km2) for durations up to 72 hours in the Colorado River or Great Basin drainages. The material for preparing an estimate makes up only a small portion of this text; the bulk of the report consists of data and studies required to develop the criteria. The local-storm criteria presented in this report also cover the Pacific Ocean drainage of California.