A major consideration for forecasters in the central and eastern United States is the northward return of low-level moisture from the Gulf of Mexico. The interaction of low-level moisture with an approaching upper-level trough has significant forecast implications with regard to heavy rainfall and severe weather potential.

The common synoptic pattern for a return flow event features a surface anticyclone moving across the southeast states, with southerly winds on its west side transporting moist air northward. This paper, however, examines several mesoscale processes in the Eta model that impact this synoptic situation. In particular, the model's parameterizations of shallow convection, evaporation from the warm water and from the moist soil over the continent, and boundary layer mixing all have a significant impact on the forecasts of return moisture flow. Model experiments are conducted on several relevant cases from 2000 and 2001.