August 22, 2003 Severe Weather and Flash Flood Event

On August 22, 2003, a cluster of thunderstorms formed over north-central and east-central Kentucky within a hot, humid air mass along and ahead of a cold front. The storms moved south and produced a number of instances of trees and power lines down. While the event was primarily a severe weather (damaging wind) concern, a flash flood occurred in the middle of the area of convection over Franklin County, Kentucky in east-central Kentucky. This occurred as convective cells repeatedly "trained" (or moved) over the same location producing a long period of heavy rainfall that resulted in rapidly flowing swollen streams and two flash flood-related deaths. Flash flood warnings were issued in advance, despite no initial reports of flooding in the area.

Animation of KLVX Doppler radar imagery on Aug 22, 2003. Note that the movement of individual thunderstorms was to the southeast. However, cells continued to redevelop and move over the same part of northern Franklin County (black circle in image above-right). This resulted in localized flash flooding within a complex of thunderstorms that otherwise produced some wind damage (trees/pwer lines down). KLVX WSR-88D Doppler radar reflectivity image at 1948 UTC (3:48 pm EDT) on Aug 22, 2003. A cluster of thunderstorms was ongoing over parts of north-central and east-central Kentucky, including within the black circle where localized flash flooding occurred as a number of storms redeveloped and moved over the same area.
A reflectivity vertical cross-section showed multiple individual thunderstorms with echo tops near 50,000. However, highest reflectivity values (red colors) were in the lower half of each storm. Such storms are called "low-centroid," and may not produce significant severe weather, but often are very efficient heavy rainfall producers. When such storms move over the same area, flash flooding can result. Visible satellite image of the tops of the thunderstorm complex over northern Kentucky, within which numerous individual thunderstorms produced strong wind gusts and very heavy rainfall. Overlaid on the satellite image is current surface weather observations and dashed lines of lifted index (which revealed a very unstable air mass at this time).
KLVX Doppler radar estimates of one-hour precipitation amounts over a portion of east-central Kentucky. Over northern Franklin County, the radar estimated amounts of 3-4 inches in one hour, which resulted in localized flash flooding. High estimates also were over Scott County. KLVX Doppler radar estimates of storm total precipitation amounts over a portion of east-central Kentucky. For the duration of the event, the radar estimated 5-6 inches of rain in northern Franklin County due to repeated training of thunderstorms over the same location.

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