The New NMC Mesoscale Eta Model: Description and Forecast Examples

Abstract

In mid-1994 a new version of the Eta Model will begin producing operational forecast guidance down to mesoscale ranges. This version will have a horizontal resolution of approximately 30 km and about 50 layers in the vertical. A summary of the primary aspects of the model is presented that includes a description of the eta coordinate and of the dynamical and physical components. Advantages of the mesoscale model are indicated in precipitation skill scores for November 1993. Specific examples are discussed that describe the mesoscale model's ability to capture small-scale circulations under fundamentally different circumstances: (i) the propagation of a strong cold front where the forcing was primarily internal and not orographic; and (ii) a rainfall event where the forcing arose from the interaction of topography with the synoptic-scale flow. Abstract In mid-1994 a new version of the Eta Model will begin producing operational forecast guidance down to mesoscale ranges. This version will have a horizontal resolution of approximately 30 km and about 50 layers in the vertical. A summary of the primary aspects of the model is presented that includes a description of the eta coordinate and of the dynamical and physical components. Advantages of the mesoscale model are indicated in precipitation skill scores for November 1993. Specific examples are discussed that describe the mesoscale model's ability to capture small-scale circulations under fundamentally different circumstances: (i) the propagation of a strong cold front where the forcing was primarily internal and not orographic; and (ii) a rainfall event where the forcing arose from the interaction of topography with the synoptic-scale flow.