During a four-day period the AMTEX area experiences “return flow” which was air coming from the south or Southeast, though still polar air north of the front. This air was trapped under an inversion separating it from the warm, dry air aloft. The changes of intensity and height of this inversion are discussed. The local vertical displacements of the inversion were somewhat inconsistent, rising in some regions while at the same time lowering in nearby areas. The strength of the inversion varied greatly, but the potential temperature at the top of the inversion maintained about the same numerical values.