Organization and Structure of Clouds and Precipitation on the Mid-Atlantic Coast of the United States. Part II: The Mesoscale and Microscale Structures of Some Frontal Rainbands

Abstract

The mesoscale and microscale structures of the clouds and precipitation associated with a frontal system on the mid-Atlantic Coast of the United States are investigated using radar reflectivity and Doppler velocity data, surface mesonet, conventional surface, upper-air and microphysical data. The frontal structure showed similarities to a warm occlusion, with code-air advection aloft preceding cold-air advection at lower levels. Six rainbands were observed in association with the frontal system. All of these rainbands developed within the region of coverage of the NWS WSR-57 radar at Cape Hatteras, North Carolina. Two were upper-level features, associated with a prefrontal surge of cold air and the main push of cold dry air aloft. These rainbands were similar in structure to prefrontal surge and wide cold-frontal rainbands, respectively, observed on the Pacific Northwest Coast. The microphysical and small mesoscale structures of the wide cold-frontal rainband are examined. Three of the rainbands were convective and developed at different times parallel to and just east of the warm-water core of the Gulf Stream. Each of these rainbands, in turn, migrated to the east. Coincident with the dissipation of the wide cold-frontal rainband offshore, a convective rainband developed behind the leading edge of the cold, dry air aloft and a third rainband intensified over the Gulf Stream in advance of the cold, dry air at midlevels. Mechanisms for the development of the Gulf Stream rainbands and for the dissipation of the wide cold-frontal rainband are discussed.