beyond the power of any aerodynamist or meteorologist to forecast twenty-four hours before the event. Precipitation in the form of showers, likewise, depends upon complicated physical processes occurring within individual clouds. While it is possible to state something about the likelihood of precipitation of this type in a given area, it is not possible to say whether rain will fall on one or another of the islands of an atoll nor to state the exact time of the beginning and ending of individual showers, An ex- perienced meteorologist who has devoted long hours to the study of cloud forms in the tropics might make forecasts of these elements as much as an hour or two in advance. More than this should not be expected of the forecaster, PART IV Probability of Occurrence of Upper Winds with Southerly Components in the Eniwetok-Bikini Area, Winds with southerly components at Fniwetok are much less prevalent than winds with northerly components, Upper wind data ob= tained by rawinsonde equipment since 1945 have been compiled. The frequency of occurrence of winds with southerly components is shown -in the attached graph (Attachment No. 1). The upper portion of the grapn shows that winds with southerly components (i.e., east-southeast clockwise through west-southwest) have occurred about thirty-five per scent of the time during the months of March through July at levels of about 10,000 feet, The lower portion of the graph shows that southeast through southwest 173