Qn the day prior to each nuclear detonation, a formal de- tailed briefing was given to the Scientific Director, the Test Manager, and his Advisory Panel covering all foreseeable ways in which weather might influence the success and safety of the test. All such briefings included wind speeds and direction predictions to at least the maximum cloud height obtainable, expected changes in wind during the day, thermal stability, clouds, preeipitation, trajectories of aerosols, the effect of wind and thermal structure on the diffusion and deposition of effluent materials, and the maximum radiation dosages that could conceivably result on and off the Test Site. Changes. if any, from these predictions were presented at subsequent briefings just prior to arming each device. In fact one of the major factors in arriving at good predictions was the series of “wind runs” usually at one-half hour intervals up to zero time (fig. 12). Most of the programs remain in effect as a further assurance of safety in the event of the release of any radioactivity from underground tests. Radiological Surveillance Routine programs were and are conducted continuously within a radius of approximately 300 miles from the Nevada Test Site by the U.S. Public Health Service. Aircraft Monitoring Since 1962 the U.S. Public Health Service has owned and operated two aircraft for cloud sampling. Prior to this date, this function was accomplished by the U.S. Air Force. Each aircraft carried equipment to collect airborne activity both particulate and yvaseous. Both planes carried equipment for continuously monitoring the gamma radiation. Additional U.S, Air Force planes equipped for cloud samplingand tracking were available and were oncall. Arrangements were madefor the use of another special aircraft for radiological monitoring surveying at H+24 hours. The capabilities of aircraft monitoring continue to be maintained. Mobile Ground Monitoring Mobile ground monitoring: teams were deployed in the downwind sector prior to each test to supplement the routine sur- veillance which was a part of the continuous surveillance program. The downwind sector was determined by information obtained from the U.S. Weather Bureau personnel assigned to the NTS. These monitoring teams consisted of two men. Each team was equipped with beta-gamma_ survey 39