Mesoanalysis of Summertime Convergence Zones in Central and Eastern North Carolina

Abstract

It is demonstrated that it is possible to perform informative mesoanalysis of summertime convergence boundaries in the southeastern United States by combining capabilities of the new WSR-88D Doppler radar with Geostationary Operational Environmental Satellite imagery and conventional surface data. Observed phenomena are identified as thunderstorm outflow boundaries, sea-breeze fronts, horizontal convective rolls, deep synoptic-scale fronts, prefrontal troughs, shallow fronts (airmass boundaries lacking upper-level support), stationary and propagating boundaries of unknown origin, and the ?Piedmont trough,? which is apparently a new feature discovered in the course of this research. The transition zone between the Piedmont and the Coastal Plain was found to be a preferred location for convergence boundaries. An unexpectedly far inland advance of the sea breeze to central North Carolina occurred in some instances. The very sensitive ?clear air mode? of the WSR-88D radar, when used in combination with high-resolution visible satellite imagery and surface mesoanalysis, made it possible to see that so-called random thunderstorm activity is either directly initiated or strongly controlled by such convergence features. Many of these features would be too weak to detect using conventional radar. The ability to perform such mesoanalyses with operational data hinges on using all of the observing tools available, since some boundaries are either ambiguous or imperceptible in visible satellite imagery, most are nearly impossible to find in conventional surface data alone, and radar suffers from well-known sampling problems at large range. The role of radar-detected interactions between convergence boundaries in initiating convection was found to be significantly different than what has been reported in Colorado by Wilson and Schreiber. Fronts in North Carolina produced convective cells of at least 40 dBZ in every instance without the need to interact with other boundaries, whereas troughs and outflow boundaries did so 86% and 70% of the time, respectively. Boundary interactions also occur significantly more often than in Colorado, and those interactions tend to result in deep convection more frequently irrespective of their motion. These results indicate that thunderstorm nowcasting may be possible in North Carolina and surrounding regions.