Extreme Convective Rainfall and Flooding from Winter Season Extratropical Cyclones in the Mid-Atlantic Region of the US


Extreme rainfall from extratropical cyclones and the distinctive hydrology of the winter season both contribute to flood extremes in the Mid-Atlantic region. In this study, we examine extreme rainfall and flooding from a winter season extratropical cyclone that passed through the eastern U.S. on 24-25 February 2016. Extreme rainfall rates during the 24-25 February 2016 time period were produced by supercell thunderstorms; we identify supercells through local maxima in azimuthal shear fields computed from Doppler velocity measurements from WSR-88D radars. Rainfall rates approaching 250 mm h−1 from a long-lived supercell in New Jersey were measured by a Parsivel disdrometer. A distinctive element of the storm environment for the 24-25 February 2016 storm was elevated values of Convective Available Potential Energy (CAPE). We also examine the climatology of atmospheric rivers (ARs) - like the February 2016 storm - based on an identification and tracking algorithm that uses 20th Century Reanalysis fields for the 66 year period from 1950 - 2015. Climatological analyses suggest that AR frequency is increasing over the Mid-Atlantic region. An increase in AR frequency, combined with increasing frequency of elevated CAPE during the winter season over the Mid-Atlantic region could result in striking changes to the climatology of extreme floods.