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 dataset used consists of 1093 observations made over a 4-year period. The events were selected using conventional network data and a set of criteria that eliminated thunderstorms rooted in the boundary layer. 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 as determined by comparisons with both the 50-kPa and 85-kPa air. The thunderstorms are usually found in the left exit region of a low-level wind maximum (an area of horizontal deformation). The large-scale environment is strongly baroclinic with large vertical wind shear an... 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 dataset used consists of 1093 observations made over a 4-year period. The events were selected using conventional network data and a set of criteria that eliminated thunderstorms rooted in the boundary layer. 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 as determined by comparisons with both the 50-kPa and 85-kPa air. The thunderstorms are usually found in the left exit region of a low-level wind maximum (an area of horizontal deformation). The large-scale environment is strongly baroclinic with large vertical wind shear an...