During the afternoon and evening
of May 23, 2000, numerous severe thunderstorms moved southeast
across central Kentucky resulting in many reports of large hail, wind damage, and a few tornadoes. Convective
structure included several supercell storms, as strong
vertical wind shear in the atmosphere (south-southwest surface
winds and stronger west-northwest winds aloft) and ample instability
combined to produce rapid storm organization and periodic storm
rotation. One supercell in particular moved across Breckinridge
and Grayson counties in north-central Kentucky (50-60 miles southwest
of Louisville) during the afternoon hours. This storm produced
golfball to baseball size hail in Breckinridge County. It then
generated a tornado over Grayson County which struck the Leitchfield
area around 200 pm CDT (300 pm EDT) producing substantial damage
to numerous structures and homes in the region. The tornado produced
F3 damage (on the Fujita scale) at its maximum intensity in Leitchfield.
Other portions of the area received F1 and F2 damage. Below is
a series of Doppler radar images from the Ft. Knox-NWS Louisville
(KLVX) WSR-88D showing the overall evolution of this storm. A
reflectivity loop of the 5 images
below also is available.
This series of base reflectivity
data from the KLVX WSR-88D Doppler radar shows the supercell
thunderstorm about every 10 minutes on its movement from Breckinridge
County (image 1) to eastern Grayson, southwest Hardin, and northwest
Hart counties (image 5). A hook echo was present on the southwest
edge of the storm, signifying the location of the tornado across
Grayson County. Image 4 shows the storm at the time the tornado
was on the ground near Leitchfield. To the north and east of
the hook, the dark red and pink colors denoted the location of
large hail and torrential rain in the storm. Golfball to baseball
size hail was reported with the storm in Breckinridge County
with golfball hail also noted in northern/eastern Grayson County.
This image shows low-level storm-relative
motion (SRM) from the KLVX WSR-88D Doppler radar. Green (red)
color denotes storm-relative winds directed toward (away from)
the radar located at Ft. Knox to the northeast of the area shown.
A counterclockwise (cyclonic) circulation was noted along the
Breckinridge-Grayson county border indicating a developing tornado,
with strong inflow over southern Breckinridge County directed
toward the hook echo region. This image corresponds to reflectivity
image 3 above.
This SRM image 20-25 minutes later
corresponds to reflectivity image 4 above. The low-level circulation/mesocyclone
(labeled above) intensified rapidly across Grayson County resulting
in the occurrence of the tornado in Leitchfield at this time.
The mesocyclone was identified as adjacent light red (left;outbound)
and light green (right;inbound) pixels. Strong storm-relative
flow continued to be directed into the mesocyclone.
This is a reflectivity cross-section
of the supercell in western Breckinridge County (prior to reflectivity
image 1 above), which allowed a vertical assessment of the storm.
Deep, intense convection was present, signified by echo tops
above 50,000 feet and a deep suspended core of very high reflectivity
values (60-70 dBZ) up to about 40,000 feet. Thus, a strong rotating
updraft was present in the storm, which produced golfball to
baseball size hail at this time, prior to tornado production.
About 15 minutes later, the storm,
now in southern Breckinridge County, remained very intense with
echo tops around 55, 000 feet. Deep-layered, high reflectivity
values remained suspended in the storm, extending to nearly 50,000
feet. The storm continued to produce golfball size hail at this
time. Note the lower reflectivity values from about 20,000 to
40,000 feet on the left side of the image. This represented precipitation
returns in the anvil portion of the thunderstorm.