This report presents generalized estimates of probable maximum precipitation (PMP) over basins in the Northwest States. Such estimates have been made for coastal drainages of California and the United States east of the 105th meridian. Generalized PMP estimates west of the 105th meridian cover the Northwest but the scope of that study does not give the detail nor the range in basin size required by the Corps of Engineers.

Generalized estimates of probable maximum precipitation have been available for the United States east of the 105th meridian for several years. The need for similar data for the planning and design requirements of the Soil Conservation Service in the region west of the 105th meridian led that agency to cooperate with estimates for that area. This report presents generalized estimates of probable maximum precipitation for areas from a point to 400 square miles and for durations up to 24 hours.