The Madison County, Virginia, Flash Flood of 27 June 1995

Abstract

Between 25 and 27 June 1995, excessive rainfall and associated flash flooding across portions of western Virginia resulted in three fatalities and millions of dollars in damage. Although many convective storms occurred over this region during this period, two particular mesoscale convective systems that occurred on 27 June were primarily responsible for the severe event. The first system (the Piedmont storm) developed over Madison County, Virginia (eastern slopes of the Blue Ridge Mountains), and propagated slowly southward producing 100?300 mm of rain over a narrow swath of the Virginia foothills and Piedmont. The second system (the Madison storm) developed over the same area but remained quasi-stationary along the eastern slopes of the Blue Ridge for nearly 8 h producing more than 600 mm of rain. Analysis of this event indicates that the synoptic conditions responsible for initiating and maintaining the Madison storm were very similar to the Big Thompson and Fort Collins floods along the Front Range of the Rocky Mountains, as well as the Rapid City flood along the east slopes of the Black Hills of South Dakota. In all four events, an approaching shortwave aloft coupled with high-level difluence/divergence signaled the presence of local ascent and convective destabilization. A postfrontal ribbon of relatively fast-moving high-?e air, oriented nearly perpendicular to the mountain range, provided a copious moisture supply and helped focus the convection over a relatively small area. Weak middle- and upper-tropospheric steering currents favored slow-moving storms that further contributed to locally excessive rainfall. A conceptual model for the Madison?Piedmont convective systems and their synoptic environment is presented, and the similarities and differences between the Madison County flood and the Big Thompson, Fort Collins, and Rapid City floods are highlighted.