Scott County (Huntsville) Tornado
April 20, 2000
On April 20th, severe thunderstorms moved across the Cumberland Plateau of east Tennessee. The storms produced wind damage, hail up to one inch in diameter, and one tornado that was rated an F1 on the Fujita Scale. Once the storms entered the valley region of east Tennessee, they weakened and very little additional severe weather was produced.
This was the first tornado to affect the Morristown County Warning Area (CWA) in nearly two years. The last tornadoes in the CWA, before the Scott County tornado, were in Johnson and Carter counties on June 3rd, 1998. The Scott county tornado was about 20 yards wide and was on the ground for only a 1/4 to 3/8 of a mile. Also associated with the severe storm and tornado were severe straight line winds that caused damage. The damage area from the straight line winds was about 400 to 500 yards wide. The NWS survey team estimated that the winds were in the 70 to 90 mph range. Overall, 21 homes received some damage, with 7 homes receiving substantial damage. Fortunately, there were no injuries. The following five photographs show the damage from Scott County:
Radar images indicated a supercell thunderstorm over Scott county near Huntsville (labeled HNTSVL) at 9:44 p.m. EDT. The base reflectivity (0.5 degree elevation slice) showed a hook echo. Rotation can be inferred from the hook echo, which can lead to the potential of a tornado. Further up in the radar's volume coverage (at the 3.4 degree elevation slice), there is more evidence of a supercell storm over Scott county. This elevation slice was approximately 21,000 feet AGL and showed a Bounded Weak Echo Region (BWER). 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 9:44 p.m. EDT on April 20, 2000.
KMRX 3.4 degree elevation reflectivity at 9:44 p.m. EDT on April 20, 2000.
The 9:44 p.m. EDT radar data gave further evidence of strong rotation at the lowest levels of the storm. The Storm Relative Velocity Map (SRM) at this time indicated a low level mesocyclone (a thunderstorm rotating in the lowest levels of storm). The green areas indicate motion toward the Morristown radar (to the ESE of Scott county), 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. In this image, the rotation velocity was greater than 36 knots, the diameter was 1.4 nautical miles, and the shear was 0.015/s. 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 Map (SRM) at 9:44 p.m. EDT on April 20, 2000.
At 9:45 p.m. EDT, the NWS Morristown issued the tornado warning for Scott County. Then five minutes later, at 9:50 p.m., the F1 tornado touchdown briefly in Huntsville.
WFUS54 KMRX 210146
TORMRX
TNCO13-151-210215-
BULLETIN - EAS ACTIVATION REQUESTED
TORNADO WARNING
NATIONAL WEATHER SERVICE MORRISTOWN TN
945 PM EDT THU APR 20 2000
THE NATIONAL WEATHER SERVICE IN MORRISTOWN HAS ISSUED A
* TORNADO WARNING FOR...
CAMPBELL COUNTY IN EASTERN TENNESSEE
SCOTT COUNTY IN EASTERN TENNESSEE
* UNTIL 1015 PM EDT
* AT 945 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A
SEVERE THUNDERSTORM WITH A DEVELOPING TORNADO NEAR HUNTSVILLE...OR
8 MILES SOUTH OF ONEIDA...MOVING EAST AT 45 MPH. THIS WARNING IS AN
UPGRADE FROM A SEVERE THUNDERSTORM WARNING ISSUED EARLIER.
* THE TORNADO IS EXPECTED TO BE NEAR...
ELK VALLEY AROUND 1000 PM EDT
LA FOLLETTE AROUND 1010 PM EDT
FINCASTLE AROUND 1015 PM EDT
SPOTTERS HAVE REPORTED A FUNNEL CLOUD WITH THIS STORM NEAR DEER LODGE.
$$
LAT ... LON 3647 8458 3629 8455 3635 8390 3657 8394
NNNN
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