A Comparative Analysis of the Impact of Low-Level Jets and Atmospheric Rivers in the Central United States

We present a comparative analysis of atmospheric rivers (ARs) and Great Plains low<level jets (GPLLJs) in the central United States during April–September 1901–2010 using ECMWF’s Coupled Reanalysis of the Twentieth Century (CERA<20C). The analysis is motivated by a perceived need to highlight overlap and synergistic opportunities between traditionally disconnected AR and GPLLJ research. First, using the Guan–Walliser integrated vapor transport (IVT)<based AR classification and Bonner–Whiteman<based GPLLJ classification, we identify days with either an AR and/or GPLLJ spanning 15% of the central United States. These days are grouped into five event samples: 1) all GPLLJ, 2) AR GPLLJ, 3) non<AR GPLLJ, 4) AR non<GPLLJ, and 5) all AR. Then, we quantify differences in the frequency, sea-sonality, synoptic environment, and extreme weather impacts corresponding to each event sample. Over the twentieth cen-tury, April–September AR frequency remained constant whereas GPLLJ frequency significantly decreased. Of GPLLJ days, 36% are associated with a coincident AR. Relative to ARs that are equally probable from April–September, GPLLJs exhibit distinct seasonality, with peak occurrence in July. A 500<hPa geopotential height comparison shows a persistent ridge over the central United States for non<AR GPLLJ days, whereas on AR GPLLJ days, a trough<and<ridge pattern is present over western to eastern CONUS. AR GPLLJ days have 34% greater 850<hPa windspeeds, 53% greater IVT, and 72% greater 24<h precipitation accumulation than non<AR GPLLJ days. In terms of 95th<percentile 850<hPa wind speed, IVT, and 24<h precipitation, that of AR GPLLJs is 25%, 45%, and 23% greater than non<AR GPLLJs, respectively.