The majority of the literature on atmospheric rivers (ARs) focuses on studies in western coastal regions, especially in mountainous regions where orographic uplift provides an efficient mechanism for converting horizontal moisture transport into upward moisture flux. In the past several years, a growing number of papers have provided evidence that ARs may also be impactful in continental interior regions, though the meteorological conditions under which these occur are still not clear. A recent study by Slinskey et al. (2020, doi: 10.1175/JHM-D-20-0039.1), using an objective atmospheric river detection tool (ARDT), indicates that a large fraction of extreme precipitation in central North America is associated with atmospheric rivers. It is not clear whether the AR objects detected by ARDTs in central North America are dynamically similar to ARs that have been extensively studied in western coastal regions (i.e., associated with midlatitude cyclones) or whether they are associated with water vapor transported by the Great Plains Low Level Jet.

We find that ARs over the U.S. Great Plains and Mississippi River Valley are frequently associated with conditions indicative of midlatitude cyclones. We find that some of these ARs are associated with mesoscale convection (e.g., squall lines), and we identify several mechanisms that can act to convert horizontal moisture transport into upward moisture flux in the absence of strong orographic forcing: surface convergence, isentropic ascent, and convection. These results also support the notion that coastal and continental-interior ARs are driven by the same underlying synoptic conditions. We explore the sensitivity of these results to the definition of AR by using multiple ARDTs. We discuss the implications of these results for improving predictions of extreme precipitation in central North America and implications for understanding ongoing and future trends in extreme precipitation.