14.5 TERRAIN-INFLUENCED TORNADOGENESIS IN THE NORTHEASTERN UNITED STATES: AN EXAMINATION OF THE 29 MAY 1995 GREAT BARRINGTON, MASSACHUSETTS, TORNADO by Lance F. Bosart 1 , Kenneth LaPenta 3 , Anton Seimon 2 , and Michael Dickinson 4 1 Department of Earth and Atmospheric Sciences The University at Albany/SUNY 1400 Washington Avenue Albany, NY 12222 2 Earth Institute of Columbia University Lamont-Doherty Earth Observatory, IRI-Monell Building Palisades, NY 10964 3 National Weather Service Forecast Office Center for Environmental Sciences and Technology Management The University at Albany/SUNY 251 Fuller Road Albany, NY 12203 4 Accurate Environmental Forecasting Narragansett, RI 02882 1. INTRODUCTION: On 29 May 1995, a supercell thunderstorm traveling a corridor across prominent topographic landforms in the northeastern United States (US) produced an almost continuous 50 km track tornado that caused damage of up to F3 intensity (Grazulus 1997). The damage swath ranged up to 1 km in width, with severe forest destruction and structural damage reported. Maximum impact was felt in Great Barrington (GBR), Massachusetts, where widespread structural damage occurred and 3 people were killed when a vehicle was thrown more than 500 m by the tornado (Storm Data, 1995). The purpose of this paper is to conduct a detailed examination of the evolution of the GBR storm and its interaction with the complex terrain. A terrain and station/county location map with the GBR tornado track superimposed appears in Fig. 1. In its size, intensity, longevity, and most significantly, its occurrence over complex terrain, the GBR tornado represents a rare event, though it is far from unique. On occasion, tornadic storms will form over relatively flat terrain but then propagate into hilly or mountainous regions with their tornadic circulations remaining intact. Examples include the long-track Adirondack tornado in New York State in 1845 (Ludlam 1970), the Shinnston, *Corresponding author address: Lance F. Bosart, University at Albany/SUNY, Department of Earth and Atmospheric Sciences, 1400 Washington Avenue, Albany, New York 12222 USA; email: bosart@atmos.albany.edu West Virginia tornado that killed 103 during an outbreak on 23 June 1944 (Brotzman 1944; Grazulis 1993), and several tornadoes of the 31 May 1985 outbreak that propagated from eastern Ohio into the hilly terrain of northwest Pennsylvania (Storm Data, 1985; Farrell and Carlson 1989). The GBR tornado occurred over a topographic environment of comparable relief to reported Rocky Mountain tornado events (e.g., Evans and Johns 1996), although at lower overall elevations. Terrain in the Appalachian mountain system of the northeastern United States averages ~2 km lower than the Rockies; however, the magnitude of terrain variations is often comparable, especially where deeply incised river valleys are located. The hilly, forested environments that characterize most of the northeastern US interior probably determine to a large degree why, despite an abundance of intense warm season convection, relatively few tornadoes are known to occur compared to the Midwest and Great Lakes at comparable latitudes further to the west. The GBR storm was fortuitous in being observed with Doppler radar (WSR-88D) during both supercell development and the subsequent tornadic phase over complex terrain, thus providing for the opportunity to study tornadogenesis in the context of a supercell's underlying topography. Our analysis Preprints, 22nd Conference on Severe Local Storms, Hyannis, MA, 4-8 October 2004