Publication Date

12-1-2006

Degree Program

Department of Geography and Geology

Degree Type

Master of Science

Abstract

Limited research exists concerning flash flooding in the United States. However, flash floods can occur anywhere and cause more fatalities than any other weather related natural disaster. Eastern Kentucky experienced an average of 41 flash floods per year (1993-2002), yet little research exists for this region. Therefore, this paper presents an analysis of the particularly devastating flash flood event of 3-4 August 2001, which resulted in $15 million worth of property damage and two deaths. Previous studies indicate that flash floods typically occur under relatively 'benign' conditions, the most common characteristics being a quasi-stationary system and high atmospheric moisture. The slow moving nature of these systems, coupled with low dewpoint depressions, leads to the overabundance of precipitation that produces flash floods. Unfortunately, this relatively 'benign' nature of weather systems poses a challenge for accurate forecasting of flash flooding. Furthermore, severe weather threats, such as tornadoes, tend to overshadow the threats posed by flash flooding, sometimes interfering with the timely issuance of flash flood warnings. To improve the accuracy of flash flood forecasting, several methods have been developed. For instance, lightning strike density helps forecasters in the West to locate regions more likely to receive the heavy rains necessary for flash flooding. Numerical forecasting models also help forecasters, especially when necessary data does not exist for the forecast area. One such model is the Penn State/ NCAR Mesoscale Model MM5. This model consists of several options allowing for variations in climate and terrain. MM5 was used to simulate the 3-4 August 2001 flash flood event, since upper air data does not exist for Eastern Kentucky. The model used for this paper utilized the Grell parameterization scheme, which provided better results than the other parameterization schemes tested (Kain-Fritsch). The Eastern Kentucky flash flood event, like the majority of other flash flood events throughout the Contiguous United States, did in fact occur under relatively benign conditions. This event occurred as heavy rains fell ahead of a trough axis associated with a slow-moving cold front. As the west-east oriented front moved southward, it stalled along the Appalachians and pivoted, becoming southwest-northeast oriented. High atmospheric moisture existed from the surface through 500-mb ahead of the front. The winds were weak and from a northerly direction, while the stability indices indicated marginal instability throughout the event. About half of the flash floods reported during this event occurred prior to the issuance of a flash flood warning, while no record of a flash flood watch existed for any of the counties prior to flash flooding. Accurate forecasting of flash floods during this relatively benign event was further hindered by the lack of a flash flood climatology for the region.

Disciplines

Earth Sciences | Environmental Sciences