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

. (2018) show improvements to a nocturnal CI forecast by assimilating conventional and radar observations. They find that assimilating these data enhances the buoyancy and convergence prior to CI, while the radar observations aid in suppressing spurious convection and erroneous outflow boundaries. However, the observations assimilated in Degelia et al. (2018) have become routinely assimilated in operational centers and their impacts are now relatively understood. This study expands upon the

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

responsible for producing convection are fundamentally different after sunset, the impacts of storm-scale DA cannot be assumed to be the same between day and night. This study presents a novel analysis of the impacts that assimilating in situ, as well as radar, observations have on forecasts of an elevated, nocturnal CI event. On 24 June 2013, a late afternoon MCS initiated off a dryline in southwestern Kansas before dissipating in the early evening hours of 25 June ( Fig. 1 ). Operational forecasts for

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Hristo G. Chipilski, Xuguang Wang, and David B. Parsons

algorithm framework, this paper also highlights a spectrum of additional algorithm applications relevant for bore research and operational forecasting of nocturnal storms. Generally speaking, these algorithm applications can be utilized in two different ways. The first pertains to the verification of numerically simulated convective outflow boundaries. With the advance of convection-allowing NWP models, object-based verification techniques like the Method for Object-Based Diagnostic Evaluation (MODE

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Aaron Johnson and Xuguang Wang

and upper air observations from the operational National Centers for Environmental Prediction (NCEP) data stream are assimilated on the outermost 12-km domain every 3 h, followed by assimilation of NEXRAD radar observations, together with the North American Mesoscale Forecast System (NAM) Data Assimilation System (NDAS) observations on the 1-km domain ( Fig. 4 ) every 10 min. The extension of the GSI EnKF system to the assimilation of the convective-scale radar observations is described in

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Matthew D. Flournoy and Michael C. Coniglio

unavailable in real-time operational settings. If such a tool was available, forecasters would then need to compare model output with real-time observations, including gust front locations and environmental boundaries. In all, the ensemble forecasting system used here, which has since evolved into the NEWS-e ( Wheatley et al. 2015 ; Jones et al. 2016 ), showed skill in forecasting even storm-scale aspects of this mesovortex event and would be beneficial to operational forecasters once computational

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

source of initial and lateral boundary condition perturbations. All members use Noah land surface scheme ( Ek et al. 2003 ) and RRTMG radiation ( Mlawer et al. 1997 ). In this study, assimilation of surface and upper-air observations from the operational National Centers for Environmental Prediction (NCEP) data stream on the 12-km domain is conducted every 3 h from 0300 UTC 10 July through 0000 UTC 11 July. NEXRAD observations, together with the North American Mesoscale Forecast System (NAM) model

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

simultaneously (e.g., Schumacher 2015 ). Additionally, strong dynamical forcing associated with mature convection may be sufficient to lift conditionally unstable air within the near-surface stable layer to its level of free convection (LFC), enabling nocturnal convection to remain surface based (e.g., Parker 2008 ; Nowotarski et al. 2011 ; Billings and Parker 2012 ). The degree to which nocturnal convection is surface based is often uncertain and thus creates complications for forecasters, who may

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J. W. Wilson, S. B. Trier, D. W. Reif, R. D. Roberts, and T. M. Weckwerth

initiating nocturnal storms during IHOP_2002 ( Weckwerth et al. 2004 ). This current PECAN case was unique in that it was the only case where data were collected on convection initiated more than 100 km from any other storms and without a near-surface convergence line or bore causing the CI. In addition, the forecast for CI provided an opportunity to collect a considerable amount of high-resolution data from a variety of measurement systems near the time and location of the CI. Figure 1 shows the

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