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

-scale differences between MCSs across seasons, this study analyzes the anomalous synoptic environments associated with organized deep convection in both austral spring and summer in SSA. Based on previous studies in the CONUS ( Feng et al. 2019 ; Song et al. 2019 ), it is hypothesized that spring MCSs are associated with greater anomalous synoptic forcing. Because of this potential shift in synoptic forcing magnitude, we determine whether there is a relationship between anomalous synoptic forcing and MCS area

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

component, there is a similar mean upslope wind magnitude for all event types, differing by generally less than 1–2 m s −1 ( Fig. 9 ). Kirshbaum (2011) found, however, that that even somewhat small increases in the terrain-relative wind [ O (1) m s −1 ] could hamper the chances for orographic CI by disrupting or displacing the low-level convergence relative to the topographic thermal forcing. Contrary to his findings, our mean Null environments have the weakest overall terrain-perpendicular (upslope

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

to model biases. The relation between moisture and precipitation errors could serve as a proper starting point. Furthermore, global models such as GFS and ECMWF likely carry their own biases that manifest when serving as parent models for WRF simulations. To attribute errors to parent models in the context of this continental comparison, an additional study should force WRF simulations to those analyzed herein with a range of global model forecast output. Caron and Steenburgh (2020) have

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

forcing owing to the stronger deep-layer wind shear in the higher-terrain supercell inflow may have also resulted in the stronger upward vertical velocities, especially in the low to midlevels (e.g., Weisman and Rotunno 2000 ; Peters et al. 2019b , 2020b ). Overall, these results suggest that terrain-induced variations to vertical wind profiles were mainly responsible for the differences noted in convective morphology as compared to terrain induced thermodynamic variations, in line with conclusions

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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

relationship owes to the critical dependence of the linear and nonlinear dynamics forcing of vertical accelerations on vertical shear. Note that because wide updrafts provide larger volumes for hail growth (e.g., Dennis and Kumjian 2017 ), an updraft-width enhancement by the terrain-enhanced vertical wind shear may have contributed to the large hail on 10 November 2018 despite the relatively short duration of updraft rotation in the IOP4 storm; future work will explore this possible connection. Wide

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

hydrologic modeling approach is also useful in flood-prone watersheds, to evaluate the flood predictability and possible hydrologic response in a changing climate ( Moore and Clarke 1981 ; Clark et al. 2008 ; Fenicia et al. 2011 ). For this study, we use the WRF-Hydro modeling system as an uncoupled (i.e., driven by independent meteorological forcing), distributed hydrologic model over the basin to assess its capability in a flash flood hindcast and forecasting framework. WRF-Hydro is currently the

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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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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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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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