Extreme rainfall from orographic thunderstorms in the central Appalachians

The envelope curve of central Appalachian flood peaks at "small" drainage areas (less than 1000 km 2) is dominated by orographic thunderstorm systems, like the Smethport storm. Orographic thunderstorm systems that have produced catastrophic flooding in the central Appalachians are examined through observational and numerical model analyses using the Weather Research and Forecasting (WRF) model.

Analyses suggest that the frequency of catastrophic flooding varies over the central Appalachian region and that small-scale variation may be linked to the role of complex terrain in altering thunderstorm dynamics. Catastrophic flooding along the western margin of the central Appalachians is dominated by four storms that occurred on 18-19 July (1889, 1942, 1977, and 1996), which were associated with warm season extratropical systems and were characterized by rapidly moving storm elements in complex terrain.