Observations of a non-supercell tornadic thunderstorm from a Terminal Doppler Weather Radar

Pre-storm environments characterized by strong wind shear, weak instability, and strong deep layer forcing are recognized as being conducive to the development of weak to occasionally moderate tornadoes within shallow, quasi-linear convective systems (QLCS). These tornadoes are relatively common in the western Carolinas, but issuance of timely warnings for these events has proven to be very difficult due to their small, shallow nature and tendency to develop rapidly. Radar observations of previous tornadic QLCS events have noted a characteristic evolution in reflectivity imagery whereby a fracture that forms across a bulging segment in the convective line immediately precedes tornadogenesis. The resultant reflectivity pattern is often referred to as the “broken-S.” This paper will examine the case of 13 January 2006, when an F1 tornado associated with a “broken-S” signature occurred near Bessemer City, North Carolina. The tornado occurred within close proximity (24 km) of the Terminal Doppler Weather Radar (TDWR) located north of the Charlotte-Douglas International Airport. This event provided a unique opportunity to observe the structure of a non-supercell tornadic thunderstorm with high resolution data from a five-cm radar in an operational setting. Radar observations from the TDWR suggest a rear-to-front descending jet turning cyclonically around the northern segment of the line break may have played an important role in tornadogenesis in the Bessemer City storm.