Terrain-Influenced tornadogenesis in the Northeastern United States: An examination of the 29 May 1995 Great Barrington, Massachusetts, tornado

Significant (F2-F5 intensity) tornadoes in mountainous environments are rare events, but seem to have a propensity for recurrence in particular topographically configured domains. The complex terrain of the Hudson Valley region of New York State and adjacent Catskill and Berkshire mountains, where prominent north-south oriented river valleys are flanked by highlands above 800 m, represents one such region where the potential for tornadogenesis appears locally enhanced on days when the synoptic-scale environment favors supercell thunderstorm formation. This behavior is illustrated through a case study of the Great Barrington, Massachusetts, F3 tornado of 29 May 1995.

Intense tornadogenesis resulted when a supercell interacted with a sequence of prominent landforms on a day when the synoptic environment was favorable for supercell thunderstorm formation. Doppler radar observations show the storm was already supercellular but not tornadic while west of the Catskill Mountains, and that the storm’s mesocyclone intensified significantly as it passed over the eastern end of the Catskill escarpment and entered the Hudson Valley. Mesocyclone intensification and tornadogenesis appear closely related to the storm’s interaction with two separate terrain-channeled flows, both of which are clearly evident in Doppler velocity data. The initial 35-km track tornado (F2) dissipated when its parent mesocyclone weakened as it moved upslope into the Berkshires of western Massachusetts, before intensifying again in the Housatonic River Valley where tornadogenesis was repeated (F3), resulting in 3 fatalities at Great Barrington.