Of paramount importance in the preparation of forecasts was a car+ ful ~lys ie of the comprehendive, highly detailed observationsof weather conditionsas re?orted by the we~ther reconnaissance8ircraft. These plames reported such items as cloud cover at all levels, the temperature and Mmidity, winds dt flight altitude~ and winds 4 emple the surftice.AR of the tremendous amount of detailed data is shown in Appendix L In forecasting the velocity of the winds from the surface to 10,000 feet, the pressure gradixt at the surface between Wake and ~iwetok proved helpful. Thie gradient when of the order of three millibars produced winds of twelve (12) to fifteen (15) knot% and as long as the gradient maintained itself, there was little chance of the winds becoming light and v=iable. Light and variable wind conditionswere an im- portant conslderdtlonbecause a detonation under these conditions could result in a seriou~ radiologicalhazar& Upper air charts drawn twice datly for 0300 and 1500 Zebra for the 850, 700, 500, 300, and 200 millibar surfaces were found to be very helpful In forecasting upper winds to 60,000 feet. In nearly all caseu it wktapossible to maintain an adequate history of troughs and ridges. These troughs and ridges influencedthe winds as well as the weather. Much of the informationon the movanent of syst~s used in the preparation of the 72 hour outlook,,wti obtained from the upper air charta. A careful