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Severe convective weather in the warm season is a common occurrence in the high plains. The storms in the high plains are produced primarily by synoptic and mesoscale features which have been described by Doswell (1980) and Maddox et al (1981). In addition to the weather parameters involved in producing severe convective weather, local terrain can also be a factor. The effects of the large scale Rocky Mountains on development of severe thunderstorms are well known. Since the early to mid 1980s, small scale terrain has been shown to have an effect on the development of severe convective weather, primarily revealed by the PROFS (Pratte and Clark, 1983) mesoscale network in northeast Colorado at that time. Most of the recent studies have concentrated on the small scale terrain in eastern Colorado. However, Benjamin et al (1986) ran a mesoscale model with a 20 km grid spacing over the central high plains from northern New Mexico to southern Wyoming using a homogenous southerly flow from data on 25 July 1983. From that numerical study, a cyclonic turning of the boundary layer winds was observed to the north of the Palmer Divide as well as to the north of the Raton Mesa and the Cheyenne Ridge.
This paper examines the effects of the Pine Ridge in northwest Nebraska, extreme east central Wyoming and extreme southwest South Dakota on severe thunderstorm development, and the possibility of a Pine Ridge circulation. First, the climatology of severe weather in the region is examined, which suggests a concentration of severe weather to the north of the Pine Ridge. A mesoscale model is then used to examine how the topography affects horizontally homogeneous flow in a way that may favor convective initiation and/or intensification in this region. Finally, a case study with the aid of a full physics mesoscale model illustrates a typical example of convective intensification possibly due to enhanced cyclonic vorticity in the vicinity of the Pine Ridge.