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Alan Shapiro, Evgeni Fedorovich, and Joshua G. Gebauer

Rapid Update Cycle (RUC) wind analyses. In a 20-yr climatology of warm season nocturnal CI over the central and southern Great Plains, Reif and Bluestein (2017) found that 24% of the nocturnal CI episodes occurred without a nearby surface boundary. Nearly one-half of these no-boundary (NB) CI episodes were of a linear storm type, the majority of which had a preferred north–south orientation, the same preference exhibited by nocturnal low-level jets (LLJs) over the Great Plains (e.g., Hoecker 1963

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Thomas R. Parish

1. Introduction The Great Plains Turbulence Research Program was a major field experiment conducted near the town of O’Neill in north-central Nebraska from August through September of 1953 ( Lettau and Davidson 1957 ). A recurring lower-atmospheric feature documented during that study was what is now known as the Great Plains low-level jet (LLJ). Lettau (1967) noted that the LLJ occurred regularly at an elevation about 450 m above the ground, commencing after sunset and reaching a peak speed

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Evgeni Fedorovich, Jeremy A. Gibbs, and Alan Shapiro

1. Introduction The nocturnal low-level jet (LLJ) is an atmospheric boundary layer wind maximum that typically develops under dry and clear conditions after sunset. The jet reaches a peak magnitude a few hours after midnight, and then decays after sunrise with the onset of convective mixing ( Shapiro and Fedorovich 2010 ). LLJs have been observed in many locations throughout the world (see, e.g., Stensrud 1996 ; Baas et al. 2009 ; Van de Wiel et al. 2010 ) but have been most extensively

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Yun Lin, Jiwen Fan, Jong-Hoon Jeong, Yuwei Zhang, Cameron R. Homeyer, and Jingyu Wang

-scale environment favorable for storm formation and maintenance. Data from the North American Regional Reanalysis (NARR) reanalysis at 1800 UTC 1 July 2015 are presented to highlight characteristics of the synoptic-scale condition ( Fig. 2 ). The storm formed east of the short-wave trough located in Nebraska ( Fig. 2a ). The 500 hPa winds exhibit a strong jet stream and upper-level disturbance over Kansas. A surface stationary front stretched from Pennsylvania to a broad region of low pressure in Kansas ( Fig

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David B. Parsons, Kevin R. Haghi, Kelton T. Halbert, Blake Elmer, and Junhong Wang

“weakly forced” conditions, with an upscale growth beginning during the evening and reaching a maximum extent after midnight. Significant attention has been paid to the question of how these propagating envelopes of convection are maintained in this nocturnal environment (e.g., Li and Smith 2010 ; Geerts et al. 2017 ). The environment typically includes a nocturnal low-level jet (NLLJ) that transports warm, moist air northward above the stable nocturnal boundary layer (e.g., Means 1952 ; Curtis

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Shushi Zhang, David B. Parsons, and Yuan Wang

2008 ). While the conventional view of MCSs typically includes a convectively generated cold pool that lifts potentially unstable air in a well-mixed boundary layer toward its level of free convection (i.e., Houze et al. 1989 ; Rotunno et al. 1988 ), Geerts et al. (2017) argues that the dynamics of nocturnal MCSs over this region are more complicated due to the presence of a stable nocturnal boundary layer (SBL) and a nocturnal low-level jet (NLLJ). Previous investigations (e.g., Means 1952

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