The Wrentham Tornado of 2004: Evolution of a Tornadic HP Supercell from a Pronounced Splitting Bow Echo in the WFO Taunton, MA County Warning Area

A squall line, forced by an approaching cold front, developed across eastern New York State during the afternoon of August 21st 2004. A tropical air mass was in place across southern New England with surface dew points in the low and middle 70s. The convective elements moved slowly eastward across the Taunton County Warning Area (CWA) during the mid to late afternoon, producing severe weather in the form of straight line wind damage across the Interstate 84 and Interstate 95 corridors, and a F1 Tornado in Wrentham, MA, which had a track length of 6 miles.

The complex, which produced the F1 Tornado, began as a “Seahorse” shaped bow echo. The bow echo underwent a line split induced by a strong rear inflow jet (RIJ), which led to the formation of a new mesocyclone. This new mesocyclone experienced upscale growth as convection intensified in response to pronounced mid altitude radial convergence (MARC). The northern portion of the line split evolved into a tornadic HP Supercell as it moved out of northeast Rhode Island and into neighboring Massachusetts, interacting with a pre-existing moisture boundary.

This paper will present the radar evolution of this event and will examine how modest changes in the near-storm environment, enhanced by a pronounced line split, lead to tornadic development.