An analysis of the 2 July 1983 storm generating a tornado at Puerto Vilelas

A strong thunderstorm generating tornado, developed during the night of 1 July 1983 and the early morning of 2 July 1983 over the area of Resistencia (27°27' S, 59°03' W), Province of Chaco Argentina. This event was studied using radiosonde and synoptic analyses provided by the National Weather Service. Strong damages occurred in the area of Puerto Vilelas area, close to Resistencia on 2 July 1983. A detailed analysis of the storm is performed using maps at the 200, 500, 850 Hpa. and surface levels for 21 UTC 1 July, and 00 UTC to 12 UTC 2 July. Also, the hourly information of the surface station located at Resistencia airport was analyzed. This information included maximum surface wind, cloudiness hourly observations, precipitation and the radiosoundings taken at 00Z and 12Z. Strong winds related with deep convection began during the night before the occurrence of the event and continue during the early morning. At the same time the tornado was occurring, a cold front at the surface was passing through the area. Cloud observations revealed the cumulonimbus presence between 02:00 and 08:00 (local time), and the cumulus convection remained during the whole day. The synoptic 850 Hpa (00Z) indicated an entrance of moist and wet air from the north. In the southern hemisphere, the anti-clockwise curved hodograph for high values of shear favors supercellular type growth on the left flank while multicellular growth is also favored on the left flank for lower shears. In this case of study the shear exhibited high values and the hodograph had an anti-clockwise veering. The surface data set showed for this particular date (2 July 1983), the maximum surface wind (23 m/s), minimum surface pressure, maximum dew point temperature for July 1983. Further research is in pogress in order to use the NCEP reanalysis data set for this case study to obtain a more detailed description about the forcing mechanisms of the Puerto Vilelas severe storm.