The goal of this study is to improve the ability of forecasters at
NWSO Greenville-Spartanburg, SC to recognize subtle tornadic
signatures in strong winter cyclone environments. To accomplish this
task, a tornado that struck without warning near Easley (Pickers
County), SC at 910 pm EST on 7 January 1998 is being investigated.
The location is about 25 miles west-southwest of the KGSP WSR-88D.
The event occurred during the passage of a line of convection in the
warm sector of a strengthening extratropical cyclone. In spite of the
absence of traditional tornado signatures on radar, the wind damage
pattern discovered during a post-storm survey indicated a sequence of
events frequently associated with the life cycle of a tornado. The
tornado had a path length of 1.5 miles and a width of 50 to 100
yards. The most destructive phase of the tornado produced F2 darnage.
Wind damage (FO) occurred in the inflow area of the storm prior to
the point where the tornado circulation engaged the ground.
Significant wind damage (F1) also occurred north of the tornado track
in the rear flank downdraft region. The only other severe weather
reports documented in the western Carolinas and extreme northeast
Georgia were several cases of wind damage weakly linked to
convection. Thus, an examination of the Pickens County storm is heing
performed to determine if certain characteristics can be discovered
that will enhance the likelihood of warning for similar isolated
tornadoes in the future. Preliminary analysis of the event has
revealed several significant facts: The tornado-producing
thunderstorm evolved from a small, fast-moving convective system that
caused significant wind damage 90 to 100 miles to the southwest; a
persistent, well-defined mesocyclone did not exist in the 30 minutes
prior to tornadogenesis; the depth of the weak mesocyclonic
circulation decreased dramatically at about the same time the wind
damage began; the tornado formed in a splitting cell just north of a
bowing line segment in a weak line echo wave pattern; the
tornado did not occur near the maximum reflectivity in the line; and
the beginning of the damage path coincided with a rapid increase of
terrain height. Based upon the initial analysis of WSR-88D velocity
and reflectivity data, one concludes that strong mesocyclones are not
required for tornado development in the warm sectors of deepening
winter cyclones. Important environmental factors not resolved due to
the scope of this study probably contributed to tornadogenesis.
Nonetheless, the radar data derived from this investigation will
enhance the ability of forecasters to rapidly diagnose the potential
for short-lived, non- supercell tornadoes that occur in the Carolinas
during the cold season.