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Stacey M. Hitchcock and Russ S. Schumacher

front ( Schumacher 2017 , and citations therein). In both cases, cloud layer winds can lead to cell motion parallel to the boundary and training/back-building. Corfidi et al. (1996) developed a technique to forecast the instances of back-building or quasi-stationary convection using the mean cloud layer wind and the (negative of) the LLJ. This was expanded to forecast forward propagation in Corfidi (2003) . In a conceptual model in Corfidi (2003) , the gust front is thought to elongate in the

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

aerosol changes jointly and respectively affect hazardous weather events such as hailstones and tornadoes using advanced cloud microphysics and urban canopy parameterizations. The Chemistry version of the Weather Research and Forecasting Model (WRF-Chem) is employed, in which the spectral-bin microphysics (SBM) is coupled with the Model for Simulating Aerosol Interactions and Chemistry (MOSAIC; Gao et al. 2016 ). The multilayer urban canopy model Building Environment Parameterization coupled with

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W. G. Blumberg, T. J. Wagner, D. D. Turner, and J. Correia Jr.

1. Introduction The radiosonde is widely considered to be the gold standard for measuring vertical profiles of thermodynamic and kinematic variables. The in situ nature of radiosonde observations allows scientists to obtain a high-vertical-resolution (roughly every 10 m) picture of the atmosphere. Because of this, radiosondes are used for several different applications. Meteorologists use these profiles to understand the current atmospheric state, initialize models, verify model forecasts, and

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Aaron Johnson and Xuguang Wang

new cells ( Haghi et al. 2019 ). The influence on convective maintenance also results from a reduction in CIN resulting from the bore lifting ( Parker 2008 ; Haghi et al. 2019 ). Better understanding and prediction of bores is needed to improve upon the relatively low skill of precipitation forecasts during the warm season (e.g., Davis et al. 2003 ; Surcel et al. 2010 ), since most of the warm season precipitation occurs at night in the Great Plains ( Wallace 1975 ). The Plains Elevated

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Rachel L. Miller, Conrad L. Ziegler, and Michael I. Biggerstaff

2013 ). Nocturnal MCSs contribute to the well-established nocturnal precipitation maximum over the central United States during the summer months ( Maddox 1980 ; Carbone and Tuttle 2008 ; Wallace 1975 ). Achieving broad improvements in human and numerical forecasts of the formation, evolution, and intensity of nocturnal MCSs (e.g., as discussed by Ziegler 1999 ) continues to present considerable challenges, although there has been substantial recent progress in observing and modeling MCSs

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Tammy M. Weckwerth, John Hanesiak, James W. Wilson, Stanley B. Trier, Samuel K. Degelia, William A. Gallus Jr., Rita D. Roberts, and Xuguang Wang

Conceptual models of nocturnal convection initiation (NCI) are used to summarize past knowledge and new discoveries following the Plains Elevated Convection at Night (PECAN) field campaign. Thorough understanding and accurate forecasting of the timing and location of U.S. Great Plains nocturnal convection initiation (NCI) remains a challenging goal. A primary reason is that NCI is often elevated with its source air from 900 to 600 hPa (e.g., Wilson and Roberts 2006 ) and typical observing

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

turning of the ageostrophic wind in a horizontally heterogeneous LLJ ( Bonner 1966 ). Unfortunately, our current understanding of nocturnal convection initiation (CI), including the possible roles of LLJs, is incomplete. Accordingly, forecasting such CI over the Great Plains remains a difficult problem, particularly when the convection initiates away from a surface boundary or previous convection and in a region of the LLJ other than the northern terminus (so-called pristine CI). This latter type of

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

initiation (CI). Forecasting elevated nocturnal CI is particularly challenging since it frequently occurs in the absence of identifiable surface boundaries ( Wilson and Roberts 2006 ), which provide useful visual cues that often aid forecasting of daytime CI. Carbone et al. (2002) illustrated that nocturnal convection in the central United States often originates as eastward-propagating thunderstorms in the lee of the Rocky Mountains much earlier in the diurnal cycle. However, central U.S. nocturnal

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Thomas R. Parish

operational 12-km horizontal resolution North American Mesoscale Forecast System (NAM). Here the focus is on summertime months of June and July for a 2-yr period 2008–09 to provide a composite gridded output set with which to compare the PECAN observations. To focus on the LLJ environment, model output was selected to include only those days for which a southerly LLJ was present. Bonner (1968) lists three criteria by which the intensity of the jet is categorized that have guided the selection process

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Thomas R. Parish and Richard D. Clark

permits evaluation of the physical processes acting to force the LLJ. Observational analyses are supplemented with a high-resolution simulation using the Weather Research and Forecasting (WRF) Model, which allows comparison of the dynamics responsible during the LLJ formation. 2. Observations of the 20 June 2015 Great Plains LLJ PECAN was a large multiagency field project conducted during June and July 2015 in the Great Plains region of the United States. The overarching goal of PECAN was to better

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