Some of the largest rainfall accumulations in the world have observed have been in the central Appalachian region. A new paper that came out this week in Water Resources Research characterizes features that lead to these large orographic/convective storms that occur predominantly during the summer. Complex interactions between topography and storm dynamics are not well understood, but appear to cause these storms. Apparently, terrain plays a role in separating storms between updraft dominated (large lightning) to downdraft dominated (large rainfall rates) events.
On the western margin of the central Appalachians, the peak occurrence of these very large storms is centered on 18–19 July. Four record storms have occurred on these dates, which coincide with the seasonal maximum 24-hour rainfall accumulations exceeding 25 mm. It really surprised me how consistent the occurrences of these large storms have been on western flank of the central Appalachians. The occurrence of “terrain-locked” eastern flank storms of the central Appalachians appears to be much more variable.
This is cool paper with lots of colorful graphics of observational and model analysis of several case study storms. For those of us in the central Appalachian region, understanding these storms is critical for improving flood frequency analyses (e.g., better characterization of extreme conditions) and hazard assessments. After the recent weeks of intense storms in our region, I thought this paper warranted a blog post.
Citation: Smith, J. A., M. L. Baeck, A. A. Ntelekos, G. Villarini, and M. Steiner (2011), Extreme rainfall and flooding from orographic thunderstorms in the central Appalachians, Water Resour. Res., 47, W04514, doi:10.1029/2010WR010190.