Rainfall accumulations greater than 20 cm over 3-6 hour durations are typical of mid-mountain orographic precipitation extremes (“super-cloudbursts” in complex terrain at elevations below 2,000 m) like the recent June 2016 flashflood in West Virginia, or the off-season October 2013 event in the Central Andes among others. Beyond localized flashfloods, the flood response of such events is further amplified by the passage of successive rain-cells over the same region over a period of 2-4 days resulting in myriad landslides overpowering the regional river network. Using HCN daily rainfall, Douglas and Barros (2013) estimated a 3-day Probable Precipitation Maximum on the order of 40-60 cm with a return period of 5,000-6,000 years along the Appalachian Mountains. Douglas and Barros (2003) further showed that the maximum 6-h precipitable water (PWAT) flux inferred from the NCEP-NCAR reanalysis 1950-1997 over the region was on the order of 24 cm, close to the rainfall values estimated for the June 2016 event. Thus, was the June 2016 event a 1,000 year flood event, a 50-year PWAT event with precipitation efficiency close to one, or … ?
In this manuscript, we investigate the small-scale dynamics and microphysics of extreme rainfall along the Appalachians from West Virginia to North Carolina during June 23-27, 2016 using high resolution simulations and ground-observations to elucidate the role of 3D topography (ridge-valley organization and connectivity) vis-à-vis large-scale controls in modulating the spatial variability of orographic precipitation efficiency. Results are contrasted with Central Andes simulations of the October 2013 extreme precipitation event.
Douglas, E. and Barros, A.P., 2003: Probable Maximum Precipitation Estimation Using Multifractals: Application in the Eastern United States. J. Hydrometeorology, Vol. 4, No. 6, 1012-1024.