92nd American Meteorological Society Annual Meeting (January 22-26, 2012)

Wednesday, 25 January 2012: 4:30 PM
Flash Flooding Over the Southern Appalachians: An Abbreviated Climatology with Forecasting Methods & Techniques
Room 352 (New Orleans Convention Center )
Anthony D. Phillips, Ball State University, Muncie, IN; and D. A. Call and J. S. M. Coleman

From 1981 to 2010 flooding claimed an average of 92 lives each year in the United States. According to the National Oceanic and Atmospheric Administration (NOAA) National Weather Service (NWS), the number of flood-related fatalities (103) was second only to those of heat-related fatalities (138) in 2010. Flash flooding is especially dangerous as sudden, torrential downpours from thunderstorms can cause gullies, streams, and creeks to rise quickly and become an immediate risk to life and property. Across the southern Appalachian Mountains this threat is aggravated by steep terrain and the rapid accumulation of rainfall in narrow valleys and gorges. Additional threats for flash flooding across the region arise from non-convective events, tropical storms that move inland across the southeast United States, and the failure and instantaneous release of water being held by an ice jam or structure such as a dam or levee.

Severe storm reports were gathered from the National Climatic Data Center (NCDC) and the Storm Events Database from 1996 to 2010. An emphasis was placed on flash flood events collected after the post-modernization of the NWS in the mid-1990s when verification of storm reports became mandatory. Using a Geographic Information System (GIS), a fifteen year climatology of flash flood events was constructed to better understand the frequency and distribution of such events over the extent of the southern Appalachians. Additional case studies and forecasting techniques tailored to the southern Mountains will also be presented to aid in recognizing conditions favorable for the development of flash floods.

In total, there were 4,938 flash flood reports across the southern Appalachian Mountains from 1996 to 2010. Of those reports there were 71 fatalities and 64 injuries, many of which occurred during the evening and overnight hours. Spatially, regions with more rugged terrain (higher mean percent slope) had higher fatality rates than less rugged locales. For flash flooding to develop, several atmospheric ingredients and conditions need to be present at the right moment and over the right location. Across the southeastern United States, this occurs most frequently during the spring and summer months when the jet stream is active and large amounts of water vapor are present. The physiographic characteristics (e.g., soil type, topography, etc.) of the region play pivotal roles in the development and severity of flash floods and must also be considered in the forecasting process. The information presented will assist meteorologists and hydrologists when applied to forecasting flash flood events and benefit those who would like to gain additional knowledge about flash flood climatology across the southern Appalachians.

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