Thunderstorms above frontal surfaces in environments without positive CAPE. Part I: a climatology

Abstract

The first of two papers describing thunderstorms that occur above frontal surfaces, frequently in environments without positive convective available potential energy (CAPE), focuses on the climatology of such storms for the conterminous United States. The data set used consists of 1093 observations made over a 4-yr period. A composite of the dataset shows that the typical "elevated' thunderstorm occurs northeast of an associated surface low-pressure center, and north of a surface warm front in a region with northeasterly surface winds. The planetary boundary layer is generally very stable. The thunderstorms are usually found in the left exit region of a low-level wind maximum (an area of horizontal deformation). The events are concentrated in an area extending northward from the central Gulf Coast along the Mississippi River valley. -from Author