During the afternoon of April
16, 1998, a cluster of thunderstorms developed and moved east
across south-central Kentucky. One particular storm, a large severe
supercell, produced wind damage, very large hail, and tornadoes
across parts of Logan, Warren, Barren, Metcalfe, and Adair counties.
Baseball size (2.75 inch diameter) hail was reported over Logan
and Warren counties. The hail produced major widespread damage
to many cars, homes, and other structures in the city of Bowling
Green with damage estimated in the hundreds of millions of dollars.
Tornadoes also occurred in several counties. F1 intensity tornadoes
were reported in Logan and Warren counties with F3 (major) tornadoes
in Barren and Adair counties. Many homes and other structures
were damaged or destroyed in Barren and Adair counties with some
damage in Metcalfe county as well. The following series of Doppler
radar images from the NWS Louisville WSR-88D shows the evolution
of this severe supercell thunderstorm.
This image is a reflectivity vertical
cross-section of a large severe thunderstorm in northwest Logan
county in south-central KY (about 85 miles southwest of the radar
site). Cross-sections show the vertical structure and distribution
of heavy rain and any hail within thunderstorms. In this case,
the storm exhibited a deep, large mass of very high reflectivity
values (dark red, pink, and small purple colors) suspended aloft
(15000 to 35000 ft) in the storm. This is indicative of a strong,
cyclonically rotating updraft (mesocyclone) and large hail within
the storm. This large hail later reached the ground with baseball
size hail reported.
Ten minutes later, base reflectivity
data at the lowest radar elevation showed the large severe thunderstorm
over northern Logan county. Very heavy rain and hail were occurring
in this area (in the red colors). Although the storm already
was a supercell, some classic low-level traits were not clearly
evident at this time. Nevertheless, the storm possessed a mesocyclone
at this time which was associated with an F1 tornado.
The storm moved east into Warren
county (just west of the city of Bowling Green). Dark red and
pink colors indicated that large hail was in progress at the
surface. On the southern edge of the storm, a weak echo region
(blue and green colors) started to appear coincident with the
rotating updraft. Large hail was occurring just north of the
weak echo region/mesocyclone.
Fifteen minutes later, the storm
tracked across Warren county and Bowling Green. Widespread large
hail, some baseball size, was occurring in the city coincident
with the pink colors on the reflectivity image. In addition,
a "hook echo" and weak echo region now had become clearly
evident on the southern flank of the supercell storm, just south
and east of the large hail (pink color) area. An tornado that
produced F1-F2 damage was reported in this county.
As the storm moved into eastern
Warren and western Barren counties, it continued to exhibit classic
supercell characteristics. A well-defined hook echo was present
on the southwest side of the storm with very heavy rain and large
hail just north and east of this area. Lighter rain extended
well to the northeast of the severe portion of the storm. A tornado
was in progress at this time.
This storm-relative velocity (SRM)
image shows wind flow directed toward (green) and away (red)
from the radar located about 70-75 miles to the north of the
area shown. A strong mesocyclone was indicated along the Warren,
Barren, and Allen county border (i.e., bright red colors immediately
next to light green colors). This location was coincident with
the hook echo/weak echo region in the reflectivity image above.
The tornado was in progress in this region. Across southwest
Barren county, a broad light green area was indicative of strong
storm-relative flow into the mesocyclone, which is important
for enhancing the severity of the storm.
The supercell moved east across
Barren county still showing a hook echo and curved appearance
along its southern edge. Storm-relative flow into the storm continued
from the south. A strong mesocyclone (not shown) was present
within the hook echo's weak echo region (yellow and small green
colors). An F3 tornado was reported in Barren county near the
city of Glasgow. Hail continued just north of this area (darker
As the storm moved across northern
Metcalfe county, it appeared to weaken temporarily as the hook
became more diffuse. Nevertheless, the storm remained severe
with wind, hail, and an F1 tornado reported.
As the supercell moved into Adair
county, the areal extent of red colors lessened giving the appearance
of a weakening storm. However, forecasters are aware that radar
sampling issues must be considered for more distant storms. Also,
a closer inspection again showed a definitive hook echo and weak
echo region on the southwest side of the storm in north-central
Adair county. The storm generated a tornado with up to F3 damage
in Adair county.
The corresponding storm-relative
velocity (SRM) data at this time showed a strong mesocyclone
in existence over north-central Adair county (red/outbound colors
immediately next to the light green/inbound colors). The mesocyclone
was coincident with the hook in the reflectivity image above
and with the tornado on the ground at this time. The storm slowly
weakened as it continued east during the evening of April 16.