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

deep convection in SSA includes an enhanced South American low-level jet (SALLJ) relative to warm-season climatology that advects warm and moist air southward along the Andes Mountains from the Amazon basin into the La Plata basin of northern Argentina ( Vera et al. 2006 ; Insel et al. 2010 ; Montini et al. 2019 ; regions shown in Fig. 1 ). Simultaneously, a deep midlevel trough approaches the Andes from the west, inducing dry mid- to upper-level subsidence flow, which creates a strong capping

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Russ S. Schumacher, Deanna A. Hence, Stephen W. Nesbitt, Robert J. Trapp, Karen A. Kosiba, Joshua Wurman, Paola Salio, Martin Rugna, Adam C. Varble, and Nathan R. Kelly

demonstrating important features observed with the soundings, including destabilization processes, the South American low-level jet (SALLJ), and convectively generated cold pools. Section 5 concludes the paper. 2. Data and methods The RELAMPAGO-CACTI soundings are analyzed in this study using the dataset produced by NCAR’s Earth Observing Laboratory ( UCAR/NCAR–Earth Observing Laboratory 2020b ). This dataset was generated by processing the sounding data from different sources using a consistent

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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

the day. A strong (>25 m s −1 ) northwesterly jet at 500 hPa extending across Córdoba Province ( Fig. 2a ) was associated with this trough. Interaction of this northwesterly flow with the Andes Mountains induced a northern Argentinean low ( Seluchi et al. 2003 ) ( Fig. 2b ) that, in concert with the subtropical high over the Atlantic Ocean, enhanced low-level northerly flow throughout the day. At 850 hPa, this northerly flow was in the form of a South American low-level jet (SALLJ; e.g., Salio et

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

circulations, gravity waves, mesoscale convergence associated with low-level jets) to facilitate the local convergence of moisture below cloud base, deepen the boundary layer, lift and reduce layers of static stability, and to vertically accelerate parcels to their levels of free convection (LFC) such that they can sustainably release convective available potential energy (CAPE) (e.g., Weckwerth and Parsons 2006 ; Wilson and Roberts 2006 ; Weckwerth et al. 2019 ). Even then, parcels that do reach their

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

. 2009 ). In subtropical South America, correlations between rainfall and ENSO have been demonstrated, especially for the La Plata basin encompassing northeast Argentina, Paraguay, and southeastern Brazil. Rainfall tends to be maximized in this area during El Niño, leading to flooding within the basin ( Camilloni and Barros 2003 ; Cavalcanti et al. 2015 ). Synoptic forcing for enhanced rainfall in the La Plata basin may be provided by a stronger subtropical jet with increased cyclonic vorticity

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

’s Precipitation Radar (PR) showed that subtropical South America has some of the most extreme deep convection anywhere in the world ( Zipser et al. 2006 ; Houze et al. 2015 ). This convection tends to be orographically favored, with warm and moist air supplied by the South American low-level jet (SALLJ) from the Amazon region and convective inhibition through mechanical subsidence in the lee of the Andes ( Rasmussen and Houze 2011 , 2016 ). These storms remain close to the terrain, backbuilding over time

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

owing to the influence of midlatitude weather systems crossing the Andes, steep lapse rate midlevel air [elevated mixed layers (EMLs); Ribeiro and Bosart 2018 ], and abundant low-level moisture streaming poleward from the Amazon rainforest region in the South American low-level jet (SALLJ; Vera et al. 2006 ). Convection initiation (CI) typically occurs over the SDC owing to enhanced low-level moisture convergence and anabatic upslope flows. Previous studies of deep convective storms across South

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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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Hernán Bechis, Paola Salio, and Juan José Ruiz

moist tropical air mass to the north of the line and dry, warm air, which moves leeward of the Andes slopes in a zone of prevailing westerly flow. The regional circulation that leads to this airmass contrast is linked to the characteristics of the topography. North of 35°S the Andes block the low-level flow, forcing a mainly meridional displacement of air masses. In particular, the channeling of warm, moist air masses from low latitudes leads to the formation of the South American low-level jet

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