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John M. Peters, Erik R. Nielsen, Matthew D. Parker, Stacey M. Hitchcock, and Russ S. Schumacher

nocturnal MCSs and their EILs are essential to identifying potential sources of errors in numerical forecasts of elevated MCSs, and the analysis of such observations are currently lacking in the scientific literature. This literary gap exists because the necessary observations required for analyzing elevated MCS environments are difficult to obtain. For instance, regular upper-level observations of temperature, moisture, and wind are taken via radiosondes with a spatial density of 100–1000 km, and at a

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

problematic for NWP forecasts (e.g., Johnson and Wang 2017 ; Johnson et al. 2017 ; Stelten and Gallus 2017 ; Johnson et al. 2018 ). Reif and Bluestein (2017) note that NWP models are often tuned specifically for features that initiate surface-based convection, whereas nocturnal CI tends to be initiated by features above the boundary layer ( Corfidi et al. 2008 ). For example, the nocturnal low-level jet (LLJ), defined as a wind maximum occurring within the lowest kilometer of the atmosphere after

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

1. Introduction Warm season precipitation forecasting remains a difficult problem, as forecast accuracy is consistently higher in the cool season than in the summer ( Fritsch and Carbone 2004 ). Forecasting warm season precipitation at night provides additional challenges, as forecasts of nocturnal convective storms in the United States are less accurate than forecasts of daytime storms ( Davis et al. 2003 ). Additionally, nocturnal convection produces many flash flooding events ( Maddox et al

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Aaron Johnson, Xuguang Wang, Kevin R. Haghi, and David B. Parsons

NWP forecasts of bores and their impacts on nocturnal convection. An accurate bore simulation is dependent on an accurate representation of both the evolution of the nocturnal boundary layer and low-level jet and a correct forecast of the formation, location, temperature, and depth of the density current. These features can be separated into three key ingredients that are necessary for successful NWP forecasts of bores. First, the mesoscale environment in which the bore occurs must be accurately

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Brian J. Carroll, Belay B. Demoz, David D. Turner, and Ruben Delgado

Plains, nocturnal CI (NCI) remains challenging to forecast, especially in the absence of surface boundaries ( Wilson and Roberts 2006 ; Reif and Bluestein 2018 ; Weckwerth et al. 2019 ). This is due in part to the paucity of routine thermodynamic profiling in the PBL and the limited resolution of satellite observations within the lowest few kilometers of the atmosphere ( Kahn et al. 2011 ; Steinke et al. 2015 ; Weckwerth et al. 2019 ). Previous studies based on radiosonde and surface data or

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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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Matthew D. Flournoy and Michael C. Coniglio

of kilometers and minutes, and can develop very quickly within QLCSs ( Mahale et al. 2012 ; Newman and Heinselman 2012 ). Because of this, forecasting severe wind associated with mesovortices is a difficult problem, and the study of both (i) synoptic conditions conducive for the development of mesovortices and (ii) mechanisms forcing mesovortex genesis in QLCSs remain active areas of research. Given favorable thermodynamic conditions, 15–20 m s −1 of line-normal vertical wind shear in the

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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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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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