Probable Maximum Precipitation Pacific Northwest States Columbia River (Including Portions of Canada), Snake River and Pacific Coastal Drainages.

摘要

This study provides all-season general-storm probable maximum precipitation (PMP) estimates for durations from 1 to 72 hours for the Columbia River basin, the Snake River basin and drainages along the Pacific coast. This includes the states of Washington, Oregon, Idaho, western Montana, northwestern Wyoming and parts of Canada. PMP estimates and their seasonal variation are given for area sizes ranging from 10 to 10,000 square miles. Estimates are also provided for local-storm PMP in the region, covering durations from 15 minutes to 6 hours for drainage areas from 1 to 500 square miles. In a significant departure from its predecessor, this study extends local-storm PMP estimates to areas west of the Cascade Mountain divide. Another significant change is the lowering of 6/1-hour ratios for local storms, reducing PMP at longer durations.