The Development of the Piedmont Front and Associated Outbreak of Severe Weather on 13 March 1986

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  • 1 Department of Marine, Earth, and Atmospheric Sciences, North Carolina State University, Raleigh, North Carolina
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Abstract

An investigation was conducted of the mesoscale evolution of a quasi-stationary front, termed the Piedmont front owing to its location through the central Carolinas, and an associated outbreak of severe weather on 13 March 1986. Space-time relationships between mesoscale processes associated with the evolution of the surface front and the initiation of severe thunderstorms were studied utilizing the enhanced surface and upper-air observation networks deployed during the field phase of GALE. Surface streamline patterns, frontogenesis, and moisture-flux divergence were computed employing an objective analysis scheme.

Following the arrival at the Carolina coast of a coastal front, the Piedmont front rapidly developed along an axis of dilatation over the eastern margin of the Piedmont, while the coastal front gradually dissipated over the nearshore waters. A differential cloud cover across the Piedmont front resulted in enhanced solar insolation on the warm side of the front that strengthened frontogenesis and acted to further destabilize the atmosphere. On the afternoon of 13 March four severe thunderstorms formed in the vicinity of the Piedmont front. Three of the storms were located in the vicinity of mesolows that formed on the front Subsequently, convection organized into a squall line along the front as synoptic-scale forcing associated with a short-wave trough and cold front aloft (CFA) overtook the Piedmont front from the west.

Stability analyses indicate that on the synoptic scale only a weak to moderate potential for severe weather existed over portions of eastern North and South Carolina. However, fields of moisture-flux divergence show a mesoscale pattern of enhanced convergence well correlated with the locations of the severe thunderstorm cells. A schematic is presented that summarizes the principal factors involved in the development of the severe weather in this complex case.

Abstract

An investigation was conducted of the mesoscale evolution of a quasi-stationary front, termed the Piedmont front owing to its location through the central Carolinas, and an associated outbreak of severe weather on 13 March 1986. Space-time relationships between mesoscale processes associated with the evolution of the surface front and the initiation of severe thunderstorms were studied utilizing the enhanced surface and upper-air observation networks deployed during the field phase of GALE. Surface streamline patterns, frontogenesis, and moisture-flux divergence were computed employing an objective analysis scheme.

Following the arrival at the Carolina coast of a coastal front, the Piedmont front rapidly developed along an axis of dilatation over the eastern margin of the Piedmont, while the coastal front gradually dissipated over the nearshore waters. A differential cloud cover across the Piedmont front resulted in enhanced solar insolation on the warm side of the front that strengthened frontogenesis and acted to further destabilize the atmosphere. On the afternoon of 13 March four severe thunderstorms formed in the vicinity of the Piedmont front. Three of the storms were located in the vicinity of mesolows that formed on the front Subsequently, convection organized into a squall line along the front as synoptic-scale forcing associated with a short-wave trough and cold front aloft (CFA) overtook the Piedmont front from the west.

Stability analyses indicate that on the synoptic scale only a weak to moderate potential for severe weather existed over portions of eastern North and South Carolina. However, fields of moisture-flux divergence show a mesoscale pattern of enhanced convergence well correlated with the locations of the severe thunderstorm cells. A schematic is presented that summarizes the principal factors involved in the development of the severe weather in this complex case.

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