re ce) = ee. A critical problem in predicting fall-out iavolves forecasting the stability or lack of stability of the wind pattern after snot time. Since radioactive particle travel is determined primarily by the winds at each level, it is required that winds must be from favorable directions or vary- ing Within the outer limits on favorable directions during the time of fallout. The critical fallout period was considered to be on the order of twelve to eighteen hours for signivicant fallout to occur. The variation in time arises fram considera- tions of wind shear, with more diffuse and less significant intensities at a given time associated with large angular and speed shear. For this reason, it was required that actual wind observations 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. 5. PPRE-SHOT BRIEFINGS: The following were presented at the pre-shot command 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 camponant above. The situation cresented at H-6 hours for the subsequent 2¢ hour period (16 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 H Hour and the 72 hour cloud trajectories, which gave a fallout pattern in a narrow sector to the east northeast anda wide (140°) sector to the south with very slow resultant winds. (See Figure 1). ge- oo, Figure 2). Usel (2) Surface radex, H to H plus 6 houstwes (See (3) Outlooks for: (a) Bikini: Unfevoreble; Eniwetok: Favorable; >; Favorable, and the native populated atolis in southeast Quadrant from ground zero favorable, Since resultant winds in the direction of these areas were considered too slow to move Signivicant fallout to the atolis involved. (b) Task Force fleet: Favorable, provided ships moved out at least 50 ciles.