Search Results

You are looking at 1 - 10 of 12 items for :

  • North America x
  • RELAMPAGO-CACTI: High Impact Weather in Subtropical South America x
  • All content x
Clear All
Jeremiah O. Piersante, Russ. S. Schumacher, and Kristen L. Rasmussen


Ensemble forecasts using the WRF Model at 20-km grid spacing with varying parameterizations are used to investigate and compare precipitation and atmospheric profile forecast biases in North and South America. By verifying a 19-member ensemble against NCEP Stage IV precipitation analyses, it is shown that the cumulus parameterization (CP), in addition to precipitation amount and season, had the largest influence on precipitation forecast skill in North America during 2016-2017. Verification of an ensemble subset against operational radiosondes in North and South America finds that forecasts in both continents feature a substantial mid-level dry bias, particularly at 700 hPa, during the warm season. Case-by-case analysis suggests that large mid-level error is associated with mesoscale convective systems (MCSs) east of the high terrain and westerly subsident flow from the Rocky and Andes Mountains in North and South America. However, error in South America is consistently greater than North America. This is likely attributed to the complex terrain and higher average altitude of the Andes relative to the Rockies, which allow for a deeper low-level jet and long-lasting MCSs, both of which 20-km simulations struggle to resolve. In the wake of data availability from the RELAMPAGO field campaign, the authors hope that this work motivates further comparison of large precipitating systems in North and South America, given their high impact in both continents.

Restricted access
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

subtropical South America is the South American low-level jet (e.g., Vera et al. 2006 ; Salio et al. 2007 ; Montini et al. 2019 ). During RELAMPAGO, a sounding site at Villa de María del Río Seco (hereinafter Villa de María), located approximately 175 km north of Córdoba ( Fig. 1a ), collected daily soundings at 0900 UTC, along with other times during IOPs, to monitor the SALLJ and its potential effects on convection. The objective criteria for identifying low-level jets first introduced by Bonner

Restricted access
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

1. Introduction Satellite observations suggest that thunderstorms in southeast South America are among the most intense and deepest in the world ( Zipser et al. 2006 ), are prolific hail producers ( Cecil and Blankenship 2012 ; Mezher et al. 2012 ; Bang and Cecil 2019 ; Bruick et al. 2019 ), and often are accompanied by extreme lightning activity and flooding (e.g., Rasmussen et al. 2014 ). In Argentina specifically, thunderstorm-generated hazards adversely impact a largely urban population

Restricted access
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

1. Introduction a. Background North-central Argentina has long been recognized as home to some of the strongest thunderstorms on Earth ( Zipser et al. 2006 ; Liu et al. 2007 ; Cecil and Blankenship 2012 ). In particular, Córdoba Province and surrounding regions frequently suffer from large hail and other forms of severe convective weather ( Mezher et al. 2012 ; Bruick et al. 2019 ). This region features unique topography that includes a small mountain range called the Sierras de Córdoba (SDC

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

conducted in which the north–south model terrain (mimicking the Sierras de Córdoba in Argentina, South America) was altered by systematically varying maximum terrain height between 500 and 4500 m. The idealized numerical modeling simulations displayed systematic variations in DCI timing and location, as well as subsequent supercell intensity, updraft and downdraft structure, cold pool and rainfall characteristics, and upscale growth rates that varied with modified environmental characteristics caused by

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

) flow of all cases, while CI cases had the strongest. Due to the similarity in the terrain-perpendicular wind, there are no statistical differences in F n 8 for the CI, Fail, or Null events. Therefore, the differences in upslope flow do not appear to differentiate event types. Fig . 9. Mean terrain (SDC) relative low-level winds (lowest 100 hPa) for CI (green), Fail (blue), and Null (red) events, where the north–south line is terrain parallel and west–east is terrain perpendicular. Proximity

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

show why this region is highly favored for convective initiation and subsequent upscale growth. Convergence is maximized near the SDC due to the impingement of the South American low-level jet (SALLJ) from the north and ageostrophic midlevel flow from the south on the elevated terrain. Because of the descent of upper-level air in the lee of the Andes, a mechanical capping inversion exists over the region that inhibits convective initiation. Moisture is advected into subtropical South America from

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

1. Introduction Hail in subtropical South America can be very large ( Rasmussen et al. 2014 ) and frequent (10–30 storms per year in central Argentina; Cecil and Blankenship 2012 ), and it causes significant impacts to property and the agricultural economy in this region. Hail has been studied for more than five decades, yet relatively little is known about the storms that produce hail or the environments that support hail-producing storms in subtropical South America. Hail research in the

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

.1175/JAMC-D-14-0114.1 . 10.1175/JAMC-D-14-0114.1 Ribeiro , B. Z. , and L. F. Bosart , 2018 : Elevated mixed layers and associated severe thunderstorm environments in South and North America . Mon. Wea. Rev. , 146 , 3 – 28 , . 10.1175/MWR-D-17-0121.1 Romatschke , U. , and R. A. Houze Jr. , 2010 : Extreme summer convection in South America . J. Climate , 23 , 3761 – 3791 , . 10.1175/2010JCLI3465.1 Salio

Full access
Hernán Bechis, Paola Salio, and Juan José Ruiz

dryline is required. Some studies ( Owen 1966 ; Hoch and Markowski 2005 ; Schultz et al. 2007 ) use surface observations to manually detect drylines. Based on this approach they found that drylines are observed over the U.S. Great Plains on 32%–45% of the spring season days (April, May, and June). Duell and Van Den Broeke (2016) developed an objective algorithm to detect drylines in the Mississippi River valley (United States), where drylines are less frequent, using data from the North American

Free access