= ee. A critical problem in predicting fall-out involves forecasting the stability or lack of stability of the wind pattern after snot time. Since radioactive particle tra- vel is determined primarily by the winds at each level, i% is required that winds must be from favorable directions or varying within the outer limits on favorable directions during the time of fallout. The critioal fallout period was considered to be on the order of twelve to eightaen hours for signiticant fallout to occur. The variation in time arises from considerations of wind shear, with more diffuse and less significant in- tansities at a given time associated with large angular and speed shear. For this reason, it was Tequired that actual wind opservations and forecasts immediately before shot time and throughout shot day be continuously considered in their relation with the forecast conditions for the first twenty-four hours after the shot. S. PRE-SHOT BRIEFINGS: The following were presented at the preeshot cammand oriefings: a. eather Weather conditions during the five days prior to BRAVO indicated a favorable trend for SRAVO day with easterly winds below 15,000 feet and winds of a southerly componant above. The situation rresented at H-6 hours for the subsequent 2¢ hour period (18 hours after shot time) was satisfactory. The 24 hour period to begin 18 hours after shot time was predicted to give an unfavorable trend as northwest winds were forecast for the 10,000 to 20,000 foot levels. db. RadSafe (1) Resultant wind diagrams including latest observed winds and forecast winds for EH Hour and the 72 hour cloud trajectories, which gave a fallout pattern in ea narrow sector to the east northeast and a wide (140°) sector to the south with very glow resultant winds. (See Figure 1). gm » Re, Figure 2). (2) Surface radex, H to HE plus 6 houdthwe (Sea (3) Outlooks for: (a) Biking: Unfavorable; Eniwetok: Favorable; Ujelang: Favorable, and the native populated atol.s in southeast quacrant from ground zero favorable, since resultant winds in the direction of theze areas were considered too slow to move Significant fallout to the atolls involved. (b) Task Force fleet: Favorable, provided shins moved out at least 50 ciles.