Knox County (Powell) Tornado
May 23, 2000
On May 23rd, severe thunderstorms moved across the central east Tennessee valley producing a tornado in the Powell community of Knox county around 5 p.m. This tornado was rated an F1 on the Fujita Scale with winds estimated between 75 and 80 mph. The tornado was about 30 to 40 yards wide and was on the ground for 1/4 to 1/2 of a mile. Also associated with the severe storm and tornado, were severe straight line winds that caused damage. Overall, 2 trailer homes in the Powell community received some damage with one injury reported.
Radar images indicated a supercell thunderstorm moving southeast across the central east Tennessee valley between 4 and 6 p.m. The base reflectivity (0.5 degree elevation slice) at 4:54 p.m. indicated a Bounded Weak Echo Region (BWER) northwest of Knoxville. The BWER is a core of weaker reflectivities (the dark green area) surrounded by stronger reflectivities (the yellows, oranges, and reds). The BWER is formed by only the strongest updrafts in thunderstorms, almost always associated with an intense supercell storm.
KMRX base reflectivity image at 4:54 p.m. EDT on May 23, 2000.
The storm gave further evidence of strong rotation at the lowest levels of the storm. The Storm Relative Velocity Map (SRM) at 4:54 p.m. indicated a low level mesocyclone (a thunderstorm rotating in the lowest levels of storm) northwest of Knoxville. The green areas indicate motion toward the Morristown radar, and the red areas indicate motion away from the radar. When these two areas are next to each other, we can infer that the thunderstorm is rotating. The rotation was strong enough and tight enough for the radar to detect a Tornadic Vortex Signature (TVS), which is the red triangle on the image.
KMRX storm relative velocity image at 4:54 p.m. EDT on May 23, 2000.