A three-dimensional trajectory forecast model was used to correlate synopticscale weather patterns with the first spring appearance of the green cloverworm (GCW),Plathypena scabra(F.), moth in central Iowa. The feasibility of wind-aided migration was studied, and a comparison of outbreak and endemic years was made. The first appearance of the GCW, as determined by catches in blacklight traps and larval surveys in each year studied (1976–85), occurred during periods of sustained southerly wind flow from the suspected overwintering region. Outbreak years had more days suitable for migration than endemic years. GCW migratory behavior and atmospheric transport are proposed as the mechanism by which the GCW reaches Iowa.