An Updated and Expanded Climatology of Severe Weather Parameters for Subtropical South America as Derived from Upper Air Observations and CFSR-CFSv2 Data

This climatological investigation updates, and expands over a larger geographic domain, the work previously conducted by Nascimento and Foss (2010) in which atmospheric parameters useful to characterize severe weather environments are computed from operational soundings (00Z and 12Z; 9pm and 9am LST, respectively) from southern Brazil and northeastern Argentina. The climatology is extended for a 20-year period, from January 1996 to December 2015, and includes atmospheric profiles obtained from additional upper air meteorological stations in the region. Profiles from a total of ten upper-air meteorological stations are investigated in this study: Foz do Iguassu, Curitiba, Porto Alegre, Florianopolis, Santa Maria and Uruguaiana, in southern Brazil, and Ezeiza (Buenos Aires), Resistencia, Cordoba and Santa Rosa in Argentina. These stations are located within one of the regions in the world most susceptible for severe convective weather: the La Plata Basin.

An improved data quality control system for the soundings is employed, and the severe weather parameters are computed using the SHARPpy algorithm (Halbert et al., 2015) fully adapted to the Southern Hemisphere. A large number of convective parameters that diagnose the main atmospheric ingredients necessary for severe convection --- moisture availability, conditional instability and vertical wind shear at distinct layers --- are evaluated, as well as their monthly and seasonal distributions, and inter-annual variability within the chosen 20-yr period. The geographic variability of such parameters within the La Plata basin also will be investigated.

As part of an effort to characterize similarities and differences between the South American and North American severe weather environments, the magnitudes of the convective parameters will be compared with the respective (and well documented) climatology for the United States of America. In addition, an attempt to identify days with favorable conditions for severe thunderstorms and tornadoes in the La Plata basin will be carried out based on the regional statistical distribution of suitable combinations of parameters (e.g., days with simultaneous occurrence of moderate/high values of CAPE, vertical wind shear in deep and shallow layers, height of the lifting condensation level, lapse rates in distinct layers, etc…).

Atmospheric profiles extracted from NCEP Climate Forecast System Reanalysis (CFSR; Saha et al., 2010) and Climate Forecast System version 2 (CFSv2; Saha et al., 2014) data also will be utilized for computing convective parameters. The statistics (e.g., quantile distributions) that result from these datasets will be compared to the respective statistics obtained from the actual soundings, allowing an assessment of the adequacy of the profiles derived from CFSR-CFSV2 as surrogates for 18Z (3pm, LST) soundings for the La Plata basin.

References:

Halbert, K. T., W. G. Blumberg and P. Marsh, 2015: SHARPpy: fueling the Python cult. 5th Symposium on Advances in Modeling and Analysis Using Python & 95th American Meteorological Society Annual Meeting, Phoenix, AZ, available at https://ams.confex.com/ams/95Annual/webprogram/Paper270233.html

Nascimento, E. L., and M. Foss, 2010: A 12-yr climatology of severe weather parameters and associated synoptic patterns for subtropical South America. 25th Conference on Severe Local Storms, American Meteorological Society, Denver, CO, available at https://ams.confex.com/ams/25SLS/techprogram/paper_175790.htm.

Saha, S., and co-authors, 2010: The NCEP Climate Forecast System Reanalysis. Bull. Amer. Meteor. Soc., 91, 1015-1057.

Saha, S., and co-authors, 2014: The NCEP Climate Forecast System version 2. J. Clim., 27, 2185-2208.