An Operational Subsynoptic Advection Model (SAM)

A simple numerical model for use in short-period forecasting (up to 24 hr) in the eastern United States is described. This model has been used operationally twice daily in the National Weather Service since June 1968. The forecast cycle is determined by the needs of the forecast service rather than by the upper air observation times. All hourly surface reports available on teletype for the eastern and central United States and Canada are used as input. The mesh length is approximately 50 mi, one-fourth that used for the large-scale, hemispheric models at the National Meteorological Center (NMC). Verifications of sea-level pressure and precipitation forecasts from SAM are presented. It is concluded that the use of this relatively inexpensive model, along with the other centralized guidance produced by NMC, can be a definite help in preparing local, short-period forecasts.