Understanding the Role of Atmospheric Rivers in Heavy Precipitation in the Southeast United States

Abstract

An analysis of atmospheric rivers (ARs) as defined by an automated AR detection tool based on integrated water vapor transport (IVT) and the connection to heavy precipitation in the southeast United States (SEUS) is performed. Climatological water vapor and water vapor transport fields are compared between the U.S. West Coast (WCUS) and the SEUS, highlighting stronger seasonal variation in integrated water vapor in the SEUS and stronger seasonal variation in IVT in the WCUS. The climatological analysis suggests that IVT values above ~500 kg m−1 s−1 (as incorporated into an objective identification tool such as the AR detection tool used here) may serve as a sensible threshold for defining ARs in the SEUS. Atmospheric river impacts on heavy precipitation in the SEUS are shown to vary on an annual cycle, and a connection between ARs and heavy precipitation during the nonsummer months is demonstrated. When identified ARs are matched to heavy precipitation days (>100 mm day−1), an average match rate of ~41% is found. Results suggest that some aspects of an AR identification framework in the SEUS may offer benefit in forecasting heavy precipitation, particularly at medium- to longer-range forecast lead times. However, the relatively high frequency of SEUS heavy precipitation cases in which an AR is not identified necessitates additional careful consideration and incorporation of other critical aspects of heavy precipitation environments such that significant predictive skill might eventually result.

Vertical Dependence of Horizontal Scaling Behavior of Orographic Wind and Moisture Fields in Atmospheric Models

“…A 4-day simulation beginning from 22 June 00Z through 26 June 00Z, 2016 was conducted to track the evolution of the storm as it moved over the Appalachians toward the SE United States. Analysis of precipitable water patterns shows persistent advection along a narrow region consistent with the classical morphology of atmospheric rivers that are associated with extreme events over the central and eastern United States in recent regional studies: (1) Climatological analysis based on National Centers for Environmental Prediction Climate and Forecast System Reanalysis for 2002-2014 shows that the presence of atmospheric rivers is tied to heavy rainfalls exceeding 100 mm/d (Mahoney et al, 2016); (2) the total precipitation of such extreme events can exceed up to 200-400 mm, corresponding to 1,000 yearly rainfall in the area of western and central Kentucky and Tennessee (Douglas & Barros, 2003;Miller et al, 2019;Moore et al, 2012). Figure 3 shows the simulated cumulative rainfall patterns on June 23, 24, and 25 that show significant precipitation upstream and over the Appalachian foothills west of the continental divide ( Figure 3a) subsequently weakening as the storm crosses over the ridges and as it propagates southeastward (Figures 3b and 3c).…”

Evaluation of the moisture sources in two extreme landfalling atmospheric river events using an Eulerian WRF tracers tool

“…The relationship between ARs and flood events has been extensively analyzed for the US West Coast region (e.g., Higgins et al, 2000;Ralph et al, 2005Ralph et al, , 2006Ralph et al, , 2004Ralph et al, , 2013Bao et al, 2006;Neiman et al, 2008a, b;Leung and Qian, 2009;Dettinger, 2011;Dettinger et al, 2011;Warner et al, 2012Warner et al, , 2014Rutz et al, 2013;Kim et al, 2013), Europe (Lavers et al, 2011(Lavers et al, , 2012Villarini, 2013, 2014;Ramos et al, 2015Ramos et al, , 2016Eiras-Barca et al, 2016;Brands et al, 2016) and other regions world-wide (e.g., Mahoney et al, 2016;Mundhenk et al, 2016). It is important to better understand the physical mechanisms leading to extreme flooding associated with ARs, considering their impacts on human and natural systems and the mounting evidence that ARs are projected to become more frequent and intense in the future (e.g., Dettinger, 2011;Payne and Magnusdottir, 2015).…”

Assessment of the Extreme Rainfall Event at Nashville, TN and the Surrounding Region on May 1–3, 2010

“…This model can be used to determine the source region of an air particle using a backward trajectory over a period of days, which in this case is stepped back in time over 72 h. This flow regime from the Caribbean, termed the Maya Express by Dirmeyer and Kinter (), is one of several types of “atmospheric rivers” (Mahoney et al. ) that are responsible for rapid moisture transport from tropical regions to the midlatitudes. The highest precipitable water values ever observed in 60 years of records were measured at both Jackson, Mississippi and Nashville, Tennessee on May 1–3, 2010.…”