Search

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 United States 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 Twentieth Century Reanalysis fields for the 66-yr period from 1950 to 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. [ABSTRACT FROM AUTHOR]

In this study, we examine extremes of atmospheric water balance components through analyses of annual maxima of precipitable water and water vapor transport. Our analyses are grounded in Extreme Value Theory, using the Generalized Extreme Value (GEV) distribution as a platform for assessing water balance extremes. Annual maxima of atmospheric water balance terms are computed from North American Regional Reanalysis (NARR) fields for the 40‐year period extending from 1979 to 2018 on a grid of approximately 0.3‐degree resolution. We assess nonstationarities in the annual maximum time series through tests for monotonic trends. Estimates of the location, scale, and shape parameters for the Generalized Extreme Value (GEV) distribution are used to examine the spatial variability of water balance extremes. We focus on estimates of the GEV shape parameter, which dictates the "thickness" of the upper tail of the distribution. Estimates of the GEV shape parameter for precipitable water generally point to bounded distributions, but clusters of unbounded, thick‐tailed distributions are linked to exceptionally large record values of precipitable water associated with tropical cyclones in the Gulf of Mexico and Atlantic. Larger regions of "thick‐tailed" distributions are found for integrated water vapor transport (IVT). Non‐stationary GEV models are used to examine the impacts of trends on extremes of the atmospheric water balance. Mixtures of rare events associated with tropical cyclones and extratropical cyclones play a central role in analyses of water balance extremes. Key Points: The "upper tails" of atmospheric water balance variables are examined through Extreme Value analyses of NARR fieldsClusters of thick‐tailed distributions exist for precipitable water and vertically‐integrated water vapor fluxMonotonic trends in atmospheric water balance variables are found over the US [ABSTRACT FROM AUTHOR]