Pattern was negative. Subsequent reports at the south end of tlle pattern at 0941, 1033, 1038 and 1057 indicated contamination of 0.05 tof0.10 R/hr. This was undoubtedly the lowest portion of the stem since it wag) encoun- tered within minutes of the time forecast by the preshot air radex area and hodograph. At 1219, radiation levels of approximately 2 R/ were reported by Wilson 3 at the north end of the pattern; it is beliEved that this was some of the same fallout encountered by Wilson 2 low). (discussed be- One significant difference was noted, however, in that Willson 3 re- ported the simultaneous collection of a "white frost or snow" onj the front of the aircraft. At this time, the aircraft was ordered to the of the pattern to "cool off." The frost-like material was washefi the aircraft passed through a rain shower while responding to th@ and the aircraft's radiation background dropped markedly. fouth end off when order, Subsequent read- ings in the pattern were background, and at approximately 1430 Wilson 3 was ordered to attempt to locate the southern edge of that portion of believed to be moving west-northwest. the cloud It was suggested that Wildon 3 pro- ceed from the holding pattern to 12.5°N, 163°E and thence to Enefetak. No contamination was reported on this phase of the flight, which indicated that cloud movement was more northerly than had been presumed. Wilson 2 was directed to fly in the holding pattern from H+2 [to H+5, then search a sector east of ground zero (limiting bearings 60° d 90° true). at 1118 The first contact with the cloud was reported by Wilson at the north end of the racetrack pattern, with the radiation level re- ported at 0.850 R/hr. This was probably fallout from the southwesternmost edge of cloud segments that were moving north. Wilson 2 did not contamination at the southern end of the pattern. Bncounter Wilson 3, however, 5,000 feet (1.52 km) lower, reported radiation from approximately 0900 (establishing an upper limit of about 8,000 feet [2.45 km] Fo 1100 for clhud seg- ments moving in a southwesterly direction and confirming both thelair radex area and the hodograph). Immediately after the initial cloudjcontact, Wilson 2 proceeded east toward the previously designated search sfctor. At that time, however, the Radsafe Office desired additional infofmation concerning any possible cloud movement toward Enewetak; accordingly, 260