AN EVALUATION OF WEATHER FORSCASTS FOR YANKEE - oe an 1. Summary of weather immediately prior to Y-Days ‘two daya price to the shot the synoptic pattern showed easterly flow to 10,000 feet. From 20,000 tc 40,000 fHet, a trough oriented east-west persisted approximtelyp 4° north of the ENIWETOK=-BIKINI ares. & elockwise cell east cof MAURO dominated flow im levels 25,000 to 45,000 feet giving southerly components in these levels, On shot day minua one it was felt that the synoptia situatigg indicated that westerly flow would prevail through the northern iia Se . 2. The “eather Forecast: 3/@ cumlus, base 2,000 feet, tops 7,000 fect, occasional tops 12,000 fect; 2/8 stratocumlus, base 3,500 feet, tops 4,500 feet; 3/8 altccumlus, base 22,000 feet, tops 24,000 feets 5/8 cirrus, base 39,000 feet, tops 41,000 feet; scattered showers, &. Observed weathers 2/8 cumilus, base 1,600 feets 2/8 altostratus base 13,000 feet; 4/8 cirrostratus, base 35,000 feet. Vergy light reia showers were reported five hour@ prior to and two hours after shot tine. b. Commenta on weathers Prior to shot time Wilson flights (recon naiseance aircraft near shot site) reported 5/@ cumilus, tops 6,000 to 8,0M feet, occasional tops at 10,000 feet; 2/8 to 5/8 altccumlus and altoatratus, base 12,000 feet. One hour prior to shot time an altcetratus base was re- ported at 21,000 feet. No rain showers were reported in the target area prior to shot time. Following the detonation, 5/8 to 7/8 cirrostratua was reported, bases ranging between 55,000 and 75,000 feete 3. The Vind Forecasts HEIGHT (Thsds Ft) 90 090/60 80 70 65 60 55 50 L5 40 35 30 25 2 , Hm26 090/50 : 18 16 uy 12 Inclosure 1 090/30 080/20 o70/10 300/10 280/25 260/40 240/35 230/30 240/25 230/20 150/10 Hal7 Hee Hoty 090/65 090/55 090/55 090/35 090/20 090/08 090/05 280/30 270/35 260/40 250/37 250/31 260/20 250/12 090/20 lo/i2 180/06 200/15 200/40 260/50 260/55 240/40 220/30 240/65 300/15 090/20 110/12 180/06 200/15 200/40 260/50 240/55 220/40 229/30 230/25 260/15 210/07 320/08 090/50 - 150/10 _230/10 100/10 LtaVar 120/10 090/12 090/45 2710/10 340/06 070/05 360/02 0-8 OBSERVED WINDS. Hehour 090/45 250/Le 280/56 Missing Missing 220/34 230/23 290/14 300/15 280/19 310/10 360/01 a@,0fos 320/13 § 340/05 010/02 ‘