Eta model forecasts of return moisture flow

Recent studies (e.g. Weiss et al. 1998) have demonstrated that the NCEP Eta model continues to have problems in cases involving the return flow of moisture in the southeast U.S., especially in the cool season. The model tends to moisten the low levels of the atmosphere too quickly over the Gulf of Mexico and western Atlantic Ocean, and the model then advects these higher-than-observed dew points onto land when the synoptic pattern dictates an onshore wind. This overprediction of available moisture has a major impact on forecasts of stability parameters and convective initiation.

This study examines the problems in detail and considers possible fixes. Results of altering the model parameterization of shallow convection and evaporative processes will be shown.