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Aaron Johnson and Xuguang Wang

), upstream of the spurious convection in 10min.6cycle, has dewpoints around 58°–62°F at 2100 UTC in THOM while 10min.6cycle dewpoints are about 62°–66°F. The 10min.6cycle dewpoints are too moist, compared with the observed dewpoints of ~61°F in this area (not shown). It is in this region of excess moisture where the 10min.6cycle forecast develops spurious convection in advance of the observed MCS ( Figs. 5c,d ). The low-level air that had been advected into northwest Oklahoma and southwest Kansas by 1800

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Tammy M. Weckwerth, Kristy J. Weber, David D. Turner, and Scott M. Spuler

1. Introduction There is a long-standing and certain need for improved atmospheric moisture measurements within and just above the atmospheric boundary layer (BL; defined here to be the lowest 2–3 km above the earth’s surface). Several recent National Research Council (NRC) reports highlighted the requirement for improved moisture and wind measurements in the BL as a necessary step toward improving numerical weather prediction (NWP) and quantitative precipitation forecasting (QPF) skill ( NRC

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

al. 1997 ; Banta et al. 2002 ; Song et al. 2005 ; Banta 2008 ; Klein et al. 2016 ). These NLLJs can modulate the atmosphere in many ways resulting in weather and climate impacts for the region ( Stensrud 1996 ). The southerly NLLJ can transport moisture from the Gulf of Mexico over the central United States. This transport has been connected to the observed nocturnal maximum in warm-season precipitation in this part of the country ( Markowski and Richardson 2010 ). The NLLJ can modify the

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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

systems do not observe temperature, moisture, or wind conditions at this height with adequate temporal and spatial resolutions. To improve the understanding and forecast skill of NCI, the Plains Elevated Convection at Night (PECAN; Geerts et al. 2017 ) field campaign included NCI as a primary scientific objective. This manuscript brings together past NCI research with data from PECAN to document frequencies and forcing mechanisms of different NCI categories. While the impact of NCI in the U.S. Great

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Dylan W. Reif and Howard B. Bluestein

preferred initiation location is on the cold side of a surface boundary for events in the linear storm-type mode ( Fig. 7b ) and along a surface boundary for single-cell storm-type CI mode events ( Fig. 7c ). The linear storm type being the preferred storm type on the cold side of a surface boundary ( Fig. 7e ) could be related to the widespread conditions (the broad areal extent of the LLJ and of moisture advected up and over a quasi-stationary front) that affect convection, as well as the continuous

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

environments in which storms form. Childs et al. (2006) showed improved CI forecasts by assimilating surface observations that induced convergent boundaries through enhanced surface heat fluxes. More recently, Sobash and Stensrud (2015) found positive results by using an ensemble Kalman filter (EnKF) to assimilate mesonet and conventional surface observations. Forecast improvements were found to have resulted from a better analysis of moisture within the PBL. Additionally, the assimilation of radar

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Aaron Johnson and Xuguang Wang

amplitude, defined as the unitless ratio of postbore stable layer depth over prebore stable layer depth, as 1.4, with minimal variability at different times during the event (e.g., Fig. 2a ). Johnson et al. (2018) also presented evidence of additional lofting of moisture above the bore, which was speculated to be a result of turbulent mixing in the bore. Qualitatively, the low-level vertical motion observed by the Mobile PECAN Integrated Sounding Array (PISA) 2 lidar ( Fig. 3 ) indicates that the

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Dana Mueller, Bart Geerts, Zhien Wang, Min Deng, and Coltin Grasmick

marked by bore-relative front-to-rear flow at all levels ( Liu and Moncrieff 2000 ). A bore and its trailing waves are sometimes visually evident from the associated roll/wave clouds ( Smith 1988 ; Coleman et al. 2010 ). Bores and related gravity waves are of great interest because they can 1) modify the stability of the nocturnal SBL and thus the dispersal of pollutants; 2) transport energy, momentum, and moisture (e.g., Koch et al. 1991 ; Martin and Johnson 2008 ); 3) trigger convection (e

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Aaron Johnson, Xuguang Wang, and Samuel Degelia

nocturnal convection (e.g., Karyampudi et al. 1995 ). Understanding and improving the predictability of atmospheric bores on the nocturnal stable layer is therefore one of the primary goals of PECAN ( Parsons et al. 2013 ). The unique field observations during PECAN, such as temperature and moisture retrievals by the Atmospheric Emitted Radiance Interferometer (AERI; Turner and Löhnert 2014 ) at the FP sites, together with the forecast system described in the present paper, facilitate this goal of

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

ahead of each wave, and areas of downward motion occur behind each crest where the along-track flow is convergent. This confirms the decrease in vertical displacement with height. Potential temperature ( Fig. 10f ) shows relatively little change as the flight level is within the rather well-mixed residual layer, decreasing only slightly by net adiabatic ascent. Equivalent potential temperature ( θ e ) ( Fig. 10f ) and in situ water vapor ( Fig. 10c ) indicate that a level containing more moisture

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