A Case Study of a Mid-Atlantic Coastal Front.

A unique case of mid-Atlantic coastal frontogenesis on December 21-22, 1983 is examined to determine the evolution of the three dimensional structure of this mesoscale phenomena. Analysis of synoptic and mesoscale surface maps suggest a coastal front which moves steadily inland. However, review of temperature and wind profiles at individual stations reveals that frontogenesis actually occurs over the land in North Carolina and southern Virginia. Lagrangian and Eulerian frontogenesis process is found to be largely a result of the ageostropic flow within the cold wedge which results in weak cold air advection over the land. This northerly flow combines with a strong southerly flow over the Atlantic to increase the temperature gradient near the coastline. Analysis of kinematic variables indicates regions of relatively strong convergence and cyclonic vorticity in the region of the coastal front. Geostrophic deformation maxima coincide with the ridge of the anticyclonic bulge east of the Appalachians. Three-dimensional Lagrangian frontogenesis computations identify the shear and confluence terms as frontogenetical within the frontal zone. The tilting term is frontolytical within the frontal zone. Precipitation analyses identify the cold air side of the coastal front as favorable for enhanced precipitation. Relationships between precipitation bands and convective instability are also discussed.