Supercell tornadogenesis over complex terrain: The Great Barrington, Massachusetts, tornado on 29 May 1995

The process of tornadogenesis in complex terrain environments has received relatively little research attention to date. Here, an analysis is presented of a long-lived supercell that became tornadic over complex terrain in association with the Great Barrington, Massachusetts (GBR), F3 tornado of 29 May 1995. The GBR tornado left an almost continuous 50-1000-m-wide damage path that stretched for similar to 50 km. The apparent rarity of significant tornadogenesis in rough terrain from a supercell well documented in operational Doppler radar motivated this case study. Doppler radar observations showed that the GBR supercell possessed a midlevel mesocyclone well prior to tornadogenesis and that the mesocyclone intensified as it crossed the eastern edge of New York's Catskill Mountains and entered the Hudson Valley. Tornadogenesis occurred as the GBR mesocyclone crossed the Hudson Valley and ascended the highlands to the east. Subsequently, the mesocyclone weakened as it approached the Taconic Range in western Massachusetts before it intensified again as it moved downslope into the Housatonic Valley where it was associated with the GBR tornado. Because of a dearth of significant mesoscale surface and upper-air observations, the conclusions and inferences presented in this paper must be necessarily limited and speculative. What data were available suggested that on a day when the mesoscale environment was supportive of supercell thunderstorm development, according to conventional indicators of wind shear and atmospheric stability, topographic configurations and the associated channeling of ambient low-level flows conspired to create local orographic enhancements to tornadogenesis potential. Numerical experimentation is needed to address these inferences, speculative points, and related issues raised by the GBR case study.