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During the evening of October
24, 2001, an extensive severe squall line raced across the Ohio Valley
ahead of a powerful cold front and weather system. The line developed across
Missouri and Illinois, then moved rapidly east across Kentucky and Indiana
and into the Appalachian Mountains overnight. The squall line produced
widespread straight-line winds of 50 to 60 mph with some gusts between 60
and 80 mph across central Kentucky and south-central Indiana. This resulted
in many downed trees and power lines, and some structural damage, although major
structural damage was not reported. Damage was most significant along bowing line segments (bow
echoes) embedded within the line. There also were a few supercell
thunderstorms that developed just ahead of the line that produced large
hail. These storms then merged quickly with the rapidly moving squall line.
These mergers essentially prevented the supercells from remaining isolated
ahead of the line long enough to produce tornadoes. However, supercells were even
more common across central and northern Indiana, some of which produced
damaging tornadoes in northern Indiana. The images below show
reflectivity data from parts of the squall line as viewed from the Ft.
Knox-NWS Louisville (KLVX) WSR-88D. In addition, a reflectivity
loop of the 8 labeled images below also is available. At bottom are
two pictures showing some of the damage that occurred in Jefferson County,
Kentucky (near Louisville). |
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The above series of WSR-88D 0.5 degree
(low-level) reflectivity images show the progression of the squall line
across north-central Kentucky and south-central Indiana. The images are at
10 minute intervals (a finer temporal interval is available). The line moved
east at a speed of 50 to 60 mph. Severe thunderstorms were present along the leading
edge of the line, where a tight reflectivity gradient suggested strong
convergence, intense updrafts, and a potent gust front that produced
widespread wind damage. Behind the leading line was
lighter trailing rainfall (green and yellow colors). The images indicate
that very strong storms moved across Harrison County, Indiana, which then bowed out as they plowed across Jefferson County, Kentucky
into Shelby County. South of this bow, another bowing line segment moved across
southern Breckinridge County, then through Hardin and into Nelson
County. Large hail also
was reported in Hardin County. A reflectivity
loop of these 8 images is available in order to view the movement of the
line. |
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The 0.5 degree reflectivity image above from
Louisville shows a portion of the squall line in south-central Kentucky. At
this time, a supercell thunderstorm was embedded in the line across
west-central Barren County east of Bowling Green. Note the dark red and pink colors in the southwest part of the supercell along the
Allen/Warren/Barren County border (center of image). This
represents large hail and very heavy rain within the storm. |
Before the line reached Louisville, it raced
through southwest and south-central Indiana. The image above shows low-level
reflectivity data as the line plowed across Perry County, Indiana. Note the
intense storms within the bowing line segment in western Perry County. The
highest reflectivity values (red colors) showed a line echo wave pattern
(LEWP) within the bow, indicative of enhanced surface wind
damage. Such signatures also can be associated with transient
tornadoes. |
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The image above taken in western Jefferson
County, Kentucky shows some of the aftermath of the squall line that struck
the county on the evening of October 24. A large tree was uprooted which
fell on a house due to the force of straight-line winds associated with a
bow echo within the squall line. |
As the bow echo raced across southern Jefferson
County, Kentucky, severe straight-line winds caused a power pole to snap
(far background of image). The weight of the snapped pole that fell caused
additional poles (foreground of image) to become bent as well. |
