On the day prior to each nuclear weapons test, a formal detailed briefing was given to the Test 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, precipitation, 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 et one or more subsequent briefings just prior to arming each device. Radiological Surveillance - Routine programs were conducted continuously within a radius of approximately 300 miles from the Nevada Test Site by the U. S. Public Health Service. During each nuclear event, the capability for monitor- ing in the downwind area is intensified. Aircraft Monitoring The U. S,. Public Health Service owned and operated two aircraft for cloud sampling. Each aircraft carried equipment to collect airborne activity both particulate and gaseous. continucusly- Both planes carried equipment for monitoring the gamma radiation. Additional U. S. Air