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During the early morning hours
of May 14, 1995, a non-severe cluster of convection evolved quite
quickly into an intense severe bow echo that raced eastward across
north-central Kentucky. The bow cut a swath of major wind damage
with widespread straight-line winds over 60 mph with maximum reported
gusts around 100 mph. In addition, at least two tornadoes of F1-F2
intensity occurred along the bow as well. The strong straight-line
winds downed many trees and power lines, and damaged or destroyed
numerous buildings and other structures. Over 10 million dollars
of damage was reported in one county alone. A conference
paper is available on-line that details the evolution of this
storm complex. Below are a series of Doppler radar images from
the NWS Louisville WSR-88D showing the evolution of the bow echo. |
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Base reflectivity image at the lowest
radar elevation showed a cluster of non-severe thunderstorms
along the Ohio River west of the radar site. Heavy rain and small
hail were occurring within the red colors. Note that there was
no tight reflectivity gradient along the leading edge of the
storms, indicating minimal potential for organized wind damage
at this time. However, strong mid-altitude radial convergence
(not shown) was occurring aloft in the storms, which can initiate
strong downdrafts that subsequently produce significant surface
wind damage. Thus, the radar showed a precursor signature that
the complex of storms likely would soon intensify. |
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The intense downdrafts caused a
rapid organization and acceleration in the area of thunderstorms,
resulting in an arced line of severe storms called a bow echo.
Note that an extremely tight reflectivity gradient now existed
along the leading edge of the storms. This gradient marked the
location of a powerful gust front and very damaging straight-line
winds driven by strong dynamics, intense downdrafts, and enhanced
rear-to-front flow. A tornado also was occurring at this time
near the intersection of the northern end of the bow echo and
the east-west zone of thunderstorms in the upper right part of
the image. |
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The bow echo raced eastward across
Hardin county in north-central KY producing severe straight-line
wind damage. (The radar site at Ft. Knox in far northern Hardin
county was within the red colors in the image at left). A tight
reflectivity gradient still existed along the leading edge. Damage
was most intense along the bow apex where the line was bulged
out the greatest. While the first tornado had dissipated by this
time, a second tornado was in progress just north of the bow
apex along the Hardin-Bullitt county border. |
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The strongest part of the bow echo
moved across Bullitt and into western Nelson county at this time
(south of Louisville). Note that a wave structure ("S"
shape) existed in the highest reflectivity values (i.e., orange
and red colors) over these counties. This wave pattern often
is associated with substantial wind damage along the wave crest
and possible tornadoes near the inflection point in the wave
just north of the crest/bow apex. Indeed, in this case, a tornado
that produced F1-F2 damage was in progress over the southern
part of Bullitt county. The tornado cut a narrow, but definitive
swath of damage, although widespread straight-line wind damage
in this case far outshadowed tornado damage. |
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Corresponding storm-relative velocity
(SRM) image over southern Bullitt county. Red (green) colors
represent radial winds directed away (toward) the radar located
10-20 miles northwest of the area shown. The small bright green
area next to red colors identified the cyclonic circulation producing
the tornado at this time. The inbound (green) component of the
circulation was resolved by the radar better than the outbound
(red) component. Light red colors southwest of the tornado location
represented strong rear-to-front flow associated with strong
straight-line winds along the bow apex. Light green colors south
and east of the tornado represented strong storm-relative flow
into the leading convective line. |
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A time later, the bow echo weakened
slightly in intensity as the leading reflectivity gradient began
to relax and as the system showed less bowing along its leading
edge. Thus, while surface wind damage continued at this time,
the degree and extent of damage was less than earlier in the
system's evolution. The line of thunderstorms continued to move
eastward after this time. |
