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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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Matthew D. Parker, Brett S. Borchardt, Rachel L. Miller, and Conrad L. Ziegler

.g., Holtslag et al. 2013 ), such as were observed during PECAN. Finally, it would be of societal benefit to connect the principal elements revealed in this study (development of surface cold pools, self-organization, transition to surface-based convection, generation of mesovortices) to the pressing operational problem of nocturnal severe wind forecasting. To do so, a richer understanding of the spectrum of environmental responses to convection (cold pools, gravity waves, and bores) will likely be needed

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

, surface buoyancy forcing, atmospheric turbulence, and slope angle. Nonetheless, past numerical modeling studies have consistently shown that representing the evolving NBL and embedded NLLJs is not easily accomplished in mesoscale models, partly due to the poor performance of turbulence parameterizations applied in boundary layer schemes. NLLJ magnitude and depth are often underestimated in studies with different boundary layer parameterization schemes in the Weather Research and Forecasting (WRF

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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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David M. Loveless, Timothy J. Wagner, David D. Turner, Steven A. Ackerman, and Wayne F. Feltz

the parent density current) to provide enough lift to initiate convection, as previously shown in cases documented by Koch and Clark (1999) and Blake et al. (2017) . These results have important implications that can be applied to real-time forecasting of potential convective initiation. Operational forecasters are able to identify the presence of a bore using surface and radar observations, and may be able to infer water vapor trends based on changes to the surface water vapor concentration

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Dylan W. Reif and Howard B. Bluestein

major forecasting problems ( Davis et al. 2003 ; Trier et al. 2006 ; Surcel et al. 2010 ). One reason is that mesoscale features such as outflow boundaries and horizontal convective rolls (HCRs) are poorly sampled and are poorly resolved in many operational models ( Trier et al. 2014 ). Another complication is that the processes that lead to CI during the day are not as effective at generating convection at night. Features such as the LLJ and gravity waves (including atmospheric bores) are more

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