STRUCTURE AND EVOLUTION OF WINTER CYCLONES IN THE CENTRAL UNITED-STATES AND THEIR EFFECTS ON THE DISTRIBUTION OF PRECIPITATION .4. THE EVOLUTION OF A DRYTROUGH ON 8-9 MARCH 1992

The structure and evolution of a drytrough (i.e., a surface pressure t rough that has characteristics of both a lee trough and a dryline) fro m the southern Great Plains to the lower Mississippi Valley are descri bed using both observational data and outputs from a mesoscale model. An elevated zone of cold-air advection associated with a cold front al oft interacted with the drytrough over the southern Great Plains to fo rm a structure similar to a warm occlusion. This type of structure fig ures importantly in a new conceptual model that has been proposed for cyclones in the central United States.