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Zhixiao Zhang, Adam Varble, Zhe Feng, Joseph Hardin, and Edward Zipser

1. Introduction A deep convective cloud cluster meets the criterion for a mesoscale convective system (MCS) when its contiguous precipitation area reaches a scale of 100 km or more in one direction (e.g., Houze 1993 , 2004 ). An MCS often contains both convective towers and stratiform regions ( Houze 1993 ) and can develop mesoscale circulations during its mature stage (e.g., Houze 1993 , 2004 ; Chen and Frank 1993 ) that differentiate it from isolated deep convection. MCSs significantly

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T. Connor Nelson, James Marquis, Adam Varble, and Katja Friedrich

environments supporting it with adequate spatial and temporal resolution, as well as an incomplete understanding of environment–cloud interactions supporting growing congestus (e.g., Crook 1996 ; Weckwerth and Parsons 2006 ; Houston and Niyogi 2007 ; Lock and Houston 2014 ; Rousseau-Rizzi et al. 2017 ; Weckwerth et al. 2019 ). For CI to occur, the atmosphere requires three fundamental ingredients: static instability, moisture, and a triggering mechanism (e.g., surface airmass boundaries, orographic

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Jeremiah O. Piersante, Kristen L. Rasmussen, Russ S. Schumacher, Angela K. Rowe, and Lynn A. McMurdie

subtropical South America (SSA) are deeper and more frequent than those east of the Rocky Mountains in North America ( Zipser et al. 2006 ; Houze et al. 2015 ). Specifically, the cloud shields associated with SSA mesoscale convective systems (MCSs) are approximately 60% larger than those occurring in the continental United States (CONUS; Velasco and Fritsch 1987 ) and their precipitation areas are larger and longer lived ( Durkee et al. 2009 ; Durkee and Mote 2010 ), contributing up to ~95% of warm

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

design is provided in section 2 . Section 3 contains the results from the idealized numerical modeling simulations and related discussion, and conclusions are located in section 4 . 2. Experimental design Numerical modeling setup A series of idealized numerical model simulations were conducted using Cloud Model 1 (CM1; Bryan and Fritsch 2002 ), version 19.7. CM1 is a compressible, nonhydrostatic numerical model. The CM1 simulations were conducted with a uniform horizontal grid spacing of 500 m

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Jeremiah O. Piersante, Russ. S. Schumacher, and Kristen L. Rasmussen

temperature, it best represents the impacts of clouds and convection, which is what the CP attempts to describe. We also assess meridional wind ( υ -component wind) to identify potential LLJ errors. METv8.0 was also implemented to calculate point verification statistics, namely the bias and root-mean-square error (RMSE): (3) bias = forecast − observation, (4) RMSE = 1 n ∑ i n ⁡ ( forecast − observation ) 2 . Following the North America precipitation forecast evaluation in section 3 , we first compare RH

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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

boundary layer height estimates from soundings (PBLHT), microwave radiometer retrieved precipitable water (MWRRET), Doppler lidar retrieved horizontal and vertical winds (DLPROF), atmospheric emitted radiance interferometer (AERI)-estimated lower-tropospheric temperature and humidity (AERIOE), interpolated soundings (INTERPSONDE), and variational analysis retrieved large-scale forcing (VARANAL). Cloud products include cloud optical depth (MFRSRCLDOD), combined lidar–radar time–height cloud boundaries

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

horizontal flow convergence frequently aids convection initiation processes by forcing low-level air parcels upward, locally reducing CIN, deepening boundary layer moisture below cloud base, and providing a focal area for moist updrafts to detrain into the overlying free troposphere, reducing the negative entrainment effect ( Ziegler et al. 1997 ; Markowski and Richardson 2010 ; Moser and Lasher-Trapp 2017 ). Common mesoscale convergence features that trigger deep convection initiation (hereafter CI

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Sujan Pal, Francina Dominguez, María Eugenia Dillon, Javier Alvarez, Carlos Marcelo Garcia, Stephen W. Nesbitt, and David Gochis

environments; 2) characterize thermodynamic and microphysical properties of clouds and precipitation, convective outflow, lightning, and hail events; and 3) observe hydrometeorological interactions with convective systems ( Nesbitt 2016 ). The occurrence of convective events in this region is linked to the strengthening of topographically guided South American low-level jet (SALLJ), which brings moist air poleward, and strong convection is formed at the exit region controlled primarily by diabatic effects

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

November–18 December 2018; ) and the Cloud, Aerosol, and Complex Terrain Interactions (CACTI) field campaign (1 October 2018–30 April 2019; ). This study will contribute to a better global understanding of hailstorms to help to improve forecasting and diagnosis of hailstorms in subtropical South America. 2. Method Because of the lack of a hail-report database in subtropical South America, satellite

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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

; Salio et al. 2007 ; Rasmussen and Houze 2016 ). This poleward penetration often coincides with the deepening of a lee trough called the northern Argentinean low (NAL; Seluchi et al. 2003 ; Saulo et al. 2004 , 2007 ). The NAL enhances the local pressure gradient force, leading to poleward SALLJ penetration near the Andes, with a wind speed maxima (up to 25 m s −1 ) at 1–1.5-km altitudes as far south as 35°S ( Nicolini and Saulo 2006 ), typically maximizing at night ( Nicolini and García Skabar

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