Observed interactions between boundary-layer mesoscale frontal features during summers in the Carolinas coastal region of eastern USA

Abstract

In the Carolinas of the United States, there are two significant land-surface features, the coastline and the Sandhills (inland), over which convection frequently forms during the summer months. The Sandhills, an area of sandy soil surrounded by other soil types, extends through the central Carolinas and is often the origin of convective storms. Nearby, sea-breeze circulations form along the coastline initiating convection during summers. The interaction between the outflow from the Sandhills convection, “the Sandhills front”, and the sea-breeze front initiates and enhances deep convection in the region. The objective of this paper is to characterize and classify these mesoscale interactions, taking into account the geography and the background flow. Using radar and in situ observations, it is found that these interactions typically occur on 24% of all days in June and 36% of the days in June when synoptic forcing is weak or absent. Onshore, offshore, and southwesterly background flows result in different strengths and locations of the convection associated with these interactions. Additionally, light winds (< 3 m s−1) and moderate winds (3–6 m s−1) influence these interactions differently. Interactions between the two fronts during moderate southwesterly flow produce widespread regional precipitation with the highest precipitation amounts due to the advection of warm, moist air from the Gulf of Mexico. Interactions during light offshore winds also produce strong interactions between the sea-breeze front and the Sandhills front possibly due to opposing flows that aid in the strengthening of a well-developed sea-breeze. Interactions occur less frequently during onshore flow and have the least precipitation amounts. The sea-breeze circulation is weak in such cases.