The objective of this study was to ascertain the magnitude and distribution of rainfall over coastal waters of the northwestern United States and to compare values with those at nearby land stations. Precipitation was measured with gauges at Totem, rainfall amounts were assessed from weather reports at lightships off the coast, and precipitation frequencies at lightships and land stations were examined. Results from the three methods were quite consistent; precipitation. on at sea was only about one-third that at coastal land stations. These values are appreciably less than previous estimates of oceanic rainfall in this area, and they support the view that a significant horizontal gradient of precipitation may exist between the coast and open sea. Rainfall typically occurs both at sea and ashore on the same day, but it rains fewer hours at sea. The relative amount of rain at sea varies with the type of atmospheric system, and rainfall at the coast appears to be intensified by frictional processes. Estimates of evaporation minus precipitation are less negative than earlier ones; consideration of their relation to surface salinity leads to distributions that are in good agreement with oceanographic knowledge. The newer values suggest that in this region the heat gain by the atmosphere may be less (but moisture entrainment may be greater) than was thought. / Graduation date: 1973