An Analysis of Radar Echo Systems for the Upper Midwestern United States

Abstract

An extensive statistical study was made of the properties of radar echo systems in the upper Midwest region of the United States. Mesoscale groupings of echoes with distance scales 10?100 km and time scales 3?10 h instead of individual echoes were considered in the expectation that the former would be more relevant to deterministic short range prediction models. A total of 203 case histories for 1974 was analyzed. Statistics for the area and duration were determined for the three categories of echo systems: those associated with warm fronts, with cold fronts and with neither. Correlations with the positions of the frontal zones and relationships with upper air winds were also made. Consistent with earlier studies, it was found that the larger echo systems tend to last longer and that the direction of motion was usually somewhat to the right of upper level winds. Results provided many quantitative relationships that would be useful for prediction schemes and for developing models that carry mesoscale precipitation areas as explicit parameters.