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Stephen W. Nesbitt, Paola V. Salio, Eldo Ávila, Phillip Bitzer, Lawrence Carey, V. Chandrasekar, Wiebke Deierling, Francina Dominguez, Maria Eugenia Dillon, C. Marcelo Garcia, David Gochis, Steven Goodman, Deanna A. Hence, Karen A. Kosiba, Matthew R. Kumjian, Timothy Lang, Lorena Medina Luna, James Marquis, Robert Marshall, Lynn A. McMurdie, Ernani de Lima Nascimento, Kristen L. Rasmussen, Rita Roberts, Angela K. Rowe, Juan José Ruiz, Eliah F.M.T. São Sabbas, A. Celeste Saulo, Russ S. Schumacher, Yanina Garcia Skabar, Luiz Augusto Toledo Machado, Robert J. Trapp, Adam C. Varble, James Wilson, Joshua Wurman, Edward J. Zipser, Ivan Arias, Hernán Bechis, and Maxwell A. Grover

this end, University of Illinois (UI), CSU, Universidad de Buenos Aires (UBA), and SMN provided convection-permitting regional and global variable resolution runs over the RELAMPAGO region to supplement global numerical guidance. SMN and Centro de Investigaciones del Mar y la Atmósfera (UBA) implemented a mesoscale ensemble-based data assimilation and forecast system on NCAR’s Cheyenne supercomputer, which fostered the operational implementation of this system at SMN. Since briefings used for

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Matthew R. Kumjian, Rachel Gutierrez, Joshua S. Soderholm, Stephen W. Nesbitt, Paula Maldonado, Lorena Medina Luna, James Marquis, Kevin A. Bowley, Milagros Alvarez Imaz, and Paola Salio

be supercells that form in environments that do not stand out among those associated with more “typical” supercells producing smaller hail. The radar signatures of storms with gargantuan or giant hail often are not particularly noteworthy, either, except perhaps stronger mesocyclonic rotation and divergence aloft. This implies that features commonly used by operational meteorologists to forecast and monitor severe storms may only be subtly different for extreme-hail-producing storms, making

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Robert J. Trapp, Karen A. Kosiba, James N. Marquis, Matthew R. Kumjian, Stephen W. Nesbitt, Joshua Wurman, Paola Salio, Maxwell A. Grover, Paul Robinson, and Deanna A. Hence

south of the observing domain. The low-level flow north of the boundary had a northeasterly (i.e., upslope) component, which was also expected to aid CI, as was a northward surging cold pool generated by convective storms ongoing during the morning. However, the forecasted evolution of the boundary, terrain, and cold pool interactions relative to the evolution of CAPE and CIN was rather complex. The observational-strategy planning for IOP4 was further complicated by the operational constraint that

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Jake P. Mulholland, Stephen W. Nesbitt, Robert J. Trapp, Kristen L. Rasmussen, and Paola V. Salio

. (2012) , have revealed that most tornado and large hail reports originate from supercellular convection, whereas damaging straight-line wind gusts predominantly occur with larger mesoscale convective systems. Similar studies have been largely absent across Argentina, however, as high spatiotemporal radar, surface, and upper-air observations are sparse, and a standard severe weather reporting procedure has not yet been implemented operationally at the time of this publication. The aim of the current

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Adam C. Varble, Stephen W. Nesbitt, Paola Salio, Joseph C. Hardin, Nitin Bharadwaj, Paloma Borque, Paul J. DeMott, Zhe Feng, Thomas C. J. Hill, James N. Marquis, Alyssa Matthews, Fan Mei, Rusen Öktem, Vagner Castro, Lexie Goldberger, Alexis Hunzinger, Kevin R. Barry, Sonia M. Kreidenweis, Greg M. McFarquhar, Lynn A. McMurdie, Mikhail Pekour, Heath Powers, David M. Romps, Celeste Saulo, Beat Schmid, Jason M. Tomlinson, Susan C. van den Heever, Alla Zelenyuk, Zhixiao Zhang, and Edward J. Zipser

used global numerical weather prediction and regional convection-allowing model guidance that was run every 6–12 h by SMN, the University of Illinois, and Colorado State University (CSU). When deep convection was forecasted, AMF1 radiosonde launch frequency was increased from 4- to 3-hourly between 0900 and 2100 LT. Additional sondes were also occasionally launched from the Villa Dolores site. In addition, Geostationary Operational Environmental Satellite-16 ( GOES-16 ) mesoscale domain sectors

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Zachary S. Bruick, Kristen L. Rasmussen, and Daniel J. Cecil

, including increased instability through low-level temperature and moisture increases, an enhanced lee trough and SALLJ, and stronger upper-level jet streams. While hailstorms in subtropical South America are supported synoptically by similar conditions to those found in the United States, the storm mode and diurnal cycles of these storms are very different. As a result, they prove to be a challenge to forecast from numerical and operational perspectives, as the knowledge gained by studying U

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Jake P. Mulholland, Stephen W. Nesbitt, and Robert J. Trapp

models and human-driven ingredients-based approach forecasting of when storms grow upscale into MCSs have been shown to have low skill (e.g., Done et al. 2004 ; Hawblitzel et al. 2007 ; Weisman et al. 2013 ; Peters et al. 2017 ). Previous studies on UCG, such as Coniglio et al. (2010 , 2011) , have found that steep low-level lapse rates, high precipitable water, large convective available potential energy (CAPE), strengthening low-level horizontal convergence at the terminus of a low-level jet

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Kristen L. Rasmussen, Melissa A. Burt, Angela Rowe, Rebecca Haacker, Deanna Hence, Lorena Medina Luna, Stephen W. Nesbitt, and Julie Maertens

). During the project, the students attended all RELAMPAGO campaign forecast briefings that occurred daily at 0900 and 1700 local time. In addition to the planned activities, networking with the instrument teams and RELAMPAGO scientists was an opportunity for the students in building their professional networks. To synthesize their field experience, the students gave a short 5-min presentation at the end of the program on the observations they collected and any insights into the science of RELAMPAGO

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James N. Marquis, Adam C. Varble, Paul Robinson, T. Connor Nelson, and Katja Friedrich

1. Introduction Correctly representing moist convective processes is critical to accurately predicting regional and global weather and climate, and accompanying operational forecasting of near- and long-term hydrology and severe weather. Numerical simulations rely on a mix of cumulus, turbulence, microphysics, and planetary boundary layer parameterization schemes to represent the generation of shallow and deep moist updrafts and precipitation (e.g., Tiedtke 1989 ; Kain and Fritsch 1990

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Zachary S. Bruick, Kristen L. Rasmussen, Angela K. Rowe, and Lynn A. McMurdie

frequency for storms during El Niño. The number of pixels that went into each composite is listed in the top right corner of each panel. ENSO also modifies the synoptic environment which supports deeper convective storms during El Niño ( Figs. 4 – 5 ). While differences in the synoptic environment associated with El Niño and La Niña were discussed earlier, a more detailed look at changes to instability yields new insights. Convective available potential energy (CAPE) is often used as a forecasting

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