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Sean Stelten and William A. Gallus Jr.

-ARW model with 4-km horizontal grid spacing and 50 vertical levels. The domain spanned 1200 km × 1200 km and was centered on the initiation location of the observed PNCI. Initial and lateral boundary conditions were provided every 6 h from 12-km North American Mesoscale Forecast System (NAM) analyses. Runs began at 1200 UTC the day of the nocturnal initiation event, to capture the diurnal evolution of the boundary layer prior to the nocturnal events. The four PBL schemes used included two local mixing

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

Rapid Refresh (RAP) The Rapid Refresh (RAP) analysis was evaluated against measurements for its ability to produce observed moisture distribution and transport features. RAP is an hourly updated data assimilation and modeling system run operationally at the National Centers for Environmental Prediction (NCEP). RAP is run at 13 km horizontal grid spacing over North America. RAP output is archived hourly. The operational version during PECAN, and used in this study, was RAPv2. A comprehensive

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

-scale environment favorable for storm formation and maintenance. Data from the North American Regional Reanalysis (NARR) reanalysis at 1800 UTC 1 July 2015 are presented to highlight characteristics of the synoptic-scale condition ( Fig. 2 ). The storm formed east of the short-wave trough located in Nebraska ( Fig. 2a ). The 500 hPa winds exhibit a strong jet stream and upper-level disturbance over Kansas. A surface stationary front stretched from Pennsylvania to a broad region of low pressure in Kansas ( Fig

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David B. Parsons, Kevin R. Haghi, Kelton T. Halbert, Blake Elmer, and Junhong Wang

the Homestead site occurred aloft in the layer between ~2.5 and 4 km, followed by the subsequent lifting of a layer initially at ~1.7 km in height, and a subsequent third pulse of ascent associated with the lifting of the stable boundary layer. These three disturbances were generated by a mesoscale convective system to the west of the Homestead site with a north-northeast–south-southwest orientation ( Fig. 8 ). Since the initial upward displacement aloft did not correspond to a fine line in the

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

Abstract

While radiosondes have provided atmospheric scientists an accurate high-vertical-resolution profile of the troposphere for decades, they are unable to provide high-temporal-resolution observations without significant recurring expenses. Remote sensing technology, however, has the ability to monitor the evolution of the atmosphere in unprecedented detail. One particularly promising tool is the Atmospheric Emitted Radiance Interferometer (AERI), a passive ground-based infrared radiometer. Through a physical retrieval, the AERI can retrieve the vertical profile of temperature and humidity at a temporal resolution on the order of minutes. The synthesis of these two instruments may provide an improved diagnosis of the processes occurring in the atmosphere. This study provides a better understanding of the capabilities of the AERI in environments supportive of deep, moist convection. Using 3-hourly radiosonde launches and thermodynamic profiles retrieved from collocated AERIs, this study evaluates the accuracy of AERI-derived profiles over the diurnal cycle by analyzing AERI profiles in both the convective and stable boundary layers. Monte Carlo sampling is used to calculate the distribution of convection indices and compare the impact of measurement errors from each instrument platform on indices. This study indicates that the nonintegrated indices (e.g., lifted index) derived from AERI retrievals are more accurate than integrated indices (e.g., CAPE). While the AERI retrieval’s vertical resolution can inhibit precise diagnoses of capping inversions, the high-temporal-resolution nature of the AERI profiles overall helps in detecting rapid temporal changes in stability.

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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

critical to the formation of the nocturnal wind maximum such as discussed by Wexler (1961) . In this study, the LLJ environment is viewed through the lens of the North American Mesoscale Forecast System. Composite grids are assembled for a 5-yr period for cases of strong LLJs and non-LLJ episodes. Comparison of the gridded datasets enables key differences to be identified and offers another view into the Blackadar–Holton debate. 2. Composite grids for cases of the LLJ As part of the Plains Elevated

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Bart Geerts, David Parsons, Conrad L. Ziegler, Tammy M. Weckwerth, Michael I. Biggerstaff, Richard D. Clark, Michael C. Coniglio, Belay B. Demoz, Richard A. Ferrare, William A. Gallus Jr., Kevin Haghi, John M. Hanesiak, Petra M. Klein, Kevin R. Knupp, Karen Kosiba, Greg M. McFarquhar, James A. Moore, Amin R. Nehrir, Matthew D. Parker, James O. Pinto, Robert M. Rauber, Russ S. Schumacher, David D. Turner, Qing Wang, Xuguang Wang, Zhien Wang, and Joshua Wurman

more common than normal in the north-central Great Plains during PECAN ( Fig. 1b ). Many intensive operation periods (IOPs) were conducted near the MCS hot spot in southeastern Nebraska, where more than twice as many MCSs occurred during PECAN than on average over the past 6 years. An MCS climatology developed by NSSL reveals that the preferred region of initiation for large (>150-km length), long-lived (>5 h) nocturnal MCSs in July ( Fig. 2 ) occurs a few 100 km to the west of where such MCSs tend

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

, NWP models used by the PECAN forecasters, such as the North American Mesoscale Forecast System (NAM), Rapid Refresh (RAP), High-Resolution Rapid Refresh (HRRR), and Colorado State 4-km WRF, had strong signals for no-boundary CI on the corresponding nights. Although these models did struggle with predicting convection on 5 July, they nevertheless produced some signal of CI in the correct location. One particular numerical model that showed skill at forecasting these CI events was the RAP model

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Thomas R. Parish and Richard D. Clark

that the North American Cordillera acts as a barrier to the broad trade wind current associated with the Bermuda high. In this view, air is blocked by the topography and then becomes deflected northward. Westerly intensification of the wind east of the Rocky Mountains is compared to processes responsible for strong western oceanic boundary currents such as the Gulf Stream. While this theory has received some recent support (e.g., Ting and Wang 2006 ), Holton (1967) originally dismissed this idea

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