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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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Timothy J. Lang, Eldo E. Ávila, Richard J. Blakeslee, Jeff Burchfield, Matthew Wingo, Phillip M. Bitzer, Lawrence D. Carey, Wiebke Deierling, Steven J. Goodman, Bruno Lisboa Medina, Gregory Melo, and Rodolfo G. Pereyra

), which is physically separate from the much larger Andes range located to its west ( Fig. 1 ). The SDC interacts with the warm and moist air from the South American low-level jet (SALLJ), mechanical subsidence in the lee of the Andes, and other meteorological features to provide orographic forcing of deep, intense convection that often back builds along the terrain ( Rasmussen and Houze 2011 , 2016 ; Rasmussen et al. 2014 ; Bruick et al. 2019 ). This creates a relatively geographically confined

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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

Electrification, Lightning, And Mesoscale/microscale Processes with Adaptive Ground Observations (RELAMPAGO) field program, funded primarily by the National Science Foundation ( Nesbitt et al. 2016 ), and the complementary Clouds, Aerosols, and Complex Terrain Interactions (CACTI) field program funded by the Department of Energy Atmospheric Radiation Measurement (DOE-ARM) program ( ). The detailed justification for RELAMPAGO-CACTI, as well as

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

(LLJ), and upper-level negative geostrophic potential vorticity (weak ambient inertial instability) all favored the most rapid transition of discrete convective cells into an MCS. Furthermore, Dial et al. (2010) found that for cases of convection initiation (CI) along a frontal or similar boundary, the potential for UCG increased when the cloud-layer wind and deep-layer vertical wind shear vectors were nearly parallel to the initiating boundary. Additionally, as the magnitude of low-level forcing

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