WINDII, a limb-viewing imaging interferometer aboard the UARS satellite, was employed to count occurrences of polar mesospheric clouds (PMC's) during the ANLC-93 campaign in July, 1993. During this period large gaps formed in the PMC occurrence plots coincident with the southward extension of the visually observed NLC region. The strong southward radar winds measured on the night side at Saskatoon and a strong northward wind on the high-latitude day side from WINDII the day before the breakup event suggest that meridional transport of the PMC source conditions or particles depleted the PMC region and enriched the NLC region to cause the event. ¿ American Geophysical Union 1995