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Joshua G. Gebauer, Alan Shapiro, Evgeni Fedorovich, and Petra Klein

the region. The thunderstorms are often elevated, in the sense that storm updrafts develop in an elevated region separated from the surface by a nocturnal stable boundary layer ( Colman 1990 ; Wilson and Roberts 2006 ). One feature associated with the initiation and development of these nocturnal thunderstorms is the Great Plains low-level jet (LLJ) ( Pitchford and London 1962 ; Maddox 1983 ; Astling et al. 1985 ; Trier and Parsons 1993 ; Trier et al. 2006 ; Tuttle and Davis 2006 ). LLJs are

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Elizabeth N. Smith, Joshua G. Gebauer, Petra M. Klein, Evgeni Fedorovich, and Jeremy A. Gibbs

1. Introduction Wind maxima called nocturnal low-level jets (NLLJs) often occur during the night in the lowest kilometer of the atmosphere. In the most general sense, the NLLJ is the result of the disruption of the daytime force balance between the Coriolis, pressure gradient, and frictional forces. Once the sun sets, thermally generated turbulence decays, and the stable boundary layer (SBL) forms. The frictional force weakens above the surface, which eliminates the force balance and leads to

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Thomas R. Parish

1. Introduction Nocturnal low-level wind maxima have received considerable attention during the past few decades. In particular, the Great Plains low-level jet (LLJ) has been the topic of extensive study (e.g., Bonner 1968 ; Mitchell et al. 1995 ; Whiteman et al. 1997 ). Wind profiles in the lowest kilometer at Great Plains sites often show profound day-to-night differences. Weak southerly winds in the lowest several hundred meters often persist throughout the daylight hours only to be

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Matthew D. Flournoy and Michael C. Coniglio

for the generation of mesovortices can be augmented by the presence of a rear-inflow jet (RIJ), a relatively common feature of mature QLCSs ( Weisman 1992 ) that is frequently associated with severe winds at the surface. Severe winds may or may not be associated with low-level mesovortices, but when they are, the strongest winds are typically found within the equatorward portion of the mesovortex ( Atkins and St. Laurent 2009a ), where the motion of the system, enhanced winds in the RIJ, and

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Samuel K. Degelia, Xuguang Wang, David J. Stensrud, and Aaron Johnson

lee of the Rocky Mountains ( Carbone et al. 2002 ; Li and Smith 2010 ), convective feedbacks such as gravity waves and bores ( Carbone et al. 2002 ; Marsham et al. 2011 ), and the Great Plains low-level jet (LLJ; Pitchford and London 1962 ; Trier and Parsons 1993 ; Higgins et al. 1997 ). The LLJ is a particularly important phenomenon that provides a source of buoyancy ( Trier and Parsons 1993 ; Helfand and Schubert 1995 ; Higgins et al. 1997 ) and forcing ( Pitchford and London 1962

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Tammy M. Weckwerth and Ulrike Romatschke

maximum in the central United States. These include, but are not limited to, deep tropospheric gravity waves generated by the Rocky Mountains elevated heat source (e.g., Tripoli and Cotton 1989a , b ; Mapes et al. 2003a , b ; Warner et al. 2003 ), potential vorticity anomalies (e.g., Raymond and Jiang 1990 ; Li and Smith 2010 ), gravity waves generated by convection (e.g., Fovell et al. 2006 ), influence by the low-level jet (LLJ; Trier and Parsons 1993 ; Fritsch and Forbes 2001 ; Keene and

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Manda B. Chasteen, Steven E. Koch, and David B. Parsons

generally supported by the poleward advection of high equivalent potential temperature ( ) air by a nocturnal low-level jet (LLJ; Fritsch and Maddox 1981 ; Maddox 1983 ). The LLJ may interact with a surface front to provide a focus for convection initiation (CI; Maddox 1983 ; Trier and Parsons 1993 ; Moore et al. 2003 ) or support CI in the absence of a surface boundary ( Wilson and Roberts 2006 ; Pu and Dickinson 2014 ; Reif and Bluestein 2017 ; Gebauer et al. 2018 ). Daytime MCSs are typically

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Stanley B. Trier, James W. Wilson, David A. Ahijevych, and Ryan A. Sobash

1. Introduction Central U.S. warm-season precipitation frequencies have a pronounced diurnal maximum at night (e.g., Wallace 1975 ). Most of this nocturnal precipitation occurs within mesoscale convective systems (MCSs) including mesoscale convective complexes (MCCs; Maddox 1980 ; Fritsch et al. 1986 ), which are supported by the nocturnal low-level jet (LLJ; Blackadar 1957 ; Holton 1967 ; Du and Rotunno 2014 ; Shapiro et al. 2016 ), and warm advection with mesoscale ascent ( Maddox 1983

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Coltin Grasmick, Bart Geerts, David D. Turner, Zhien Wang, and T. M. Weckwerth

well-mixed, deep planetary boundary layer (PBL)—to elevated nocturnal convection, which typically organizes at larger scales as the nocturnal stable boundary layer (SBL) deepens, and a low-level jet (LLJ) develops above the SBL ( Corfidi et al. 2008 ; Carbone and Tuttle 2008 ; Reif and Bluestein 2017 ). Convective cells develop when a parcel of air is lofted to its level of free convection (LFC), becoming buoyant with respect to its surrounding environment. Convective cells often initiate in the

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Stacey M. Hitchcock, Russ S. Schumacher, Gregory R. Herman, Michael C. Coniglio, Matthew D. Parker, and Conrad L. Ziegler

. 2003 ; Clark et al. 2007 ; Johnson and Wang 2013 ; Johnson et al. 2013 ). MCSs span a distance of ~100 km or larger and can have a variety of organizational modes ( Parker and Johnson 2000 ; Houze 2004 ; Schumacher and Johnson 2005 ). They are often associated with a midlevel short-wave trough, a baroclinic zone (in the United States this is often a warm or stationary surface front), a statically stable boundary layer, a low-level jet (LLJ), and the associated advection of warm, moist, high θ

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