er factors and information, for weather determines the major premises upon which the radiological safety program is based. Fore- easts of radioactive fallout depend primarily on forecasts of the wind field and thus these forecasts will be no more accurate than the wind forecasts themselves. This means that the Task Force Rad~ Safe Officer must work closely with the Task Force Meteorologist in determining the outlook for any one period. In cooperation with the Meteorologist and other specialists, the RadSafe Officer can depend on such aids as: A. Winds Aloft Observations and Forecasts. The weather observational network for CASTLE consisted of stations at Eniwetok, Bikini, Rongerik, Majuro, Kusaie, Penape, and Kwajalein, with additional data coming from Midway, Wake, Marcus, Guam, Iwo Jima, and Johnston. Twice daily winds aloft runs were made as a routine matter with the number of runs being increased to as many as eight per day prior to a shot period, Planning forecasts were issued forty-eight and thirty-eight hours prior to each shot hour and consisted of winds for the shot site for each ten thousand fcot level from the surfaze to ninety thousand feet. Following the selection of a specific shot time, forecasts were issued at twenty-four, thirteen, eight, and four hour intervals pricr to H-hcur, tailed: These forecasts were much more de- winds were forecast to the nearest ten degrees and to the knot, and for each two thousand foot increment from the surface to twenty theusand feet, for each five thousand foot increment from 181