Orographic Thunderstorms and extreme floods along the western margin of the central appalachians

The Appalachian region has experienced some of the largest unit discharge flood peaks in the United States and rainfall accumulations in the world (at time intervals less than 6 hours). The 18 July 1942 Smethport, Pennsylvania produced the world record rainfall accumulation at 4 hour time scale. The record at 2 hour time scale was held for many years by the 18 July 1889 Rockport, West Virgina storm. These storms reflect two important elements of extreme rainfall climatology: 1) some of the largest measured rainfall accumulations in the world at short time intervals (less than 6 hours) have occurred in the upper Ohio River Valley and 2) the seasonal occurrence of extreme rainfall events is tightly concentrated around mid-July. In this study we characterize the climatology of extreme rainfall amd flooding in the Appalachian region of the eastern United States. Of particular interest are: a) the seasonal distribution of extreme rainfall and flooding, b) the role of orographic precipitation processes in controlling the climatology of extreme rainfall and c) the linkage between extreme rainfall and severe weather, d) and hydrometeorological controls of scale-dependent flood response. The methodology used to examine these issues centers on empirical analyses of rain gage, radar (WSR-88D volume scan reflectivity and Doppler velocity) and stream gaging data sets from the central Appalachian region.