The tornadic thunderstorm events during the 1998-1999 South African summer

Due to the occurrence of several tornadoes in the summer of 1998/99 it was decided to research the occurrence of tornadic event s over South Africa. A general overview of tornadoes is given along with a way to classify the intensity of these events. This is followed by a section on the frequency, occurrence and location of tornadoes over South Africa. Severe weather and/or tornado events can be expected when certain atmospheric conditions prevail. These are defined and indications of threshold values for s evere weather are given. Three tornadic events which occurred in 1998/99 in South Africa are then discussed by means of these parameters. The first is the Harrismith tornado in November 1998 which was classified as an F3 tornado by the Fujita-Pearson (F P) classification. The tornado which occurred in Mount Ayliff in January 1999 was seemingly the most severe ever reported FP classification F4 - and was the next case considered. Finally a short summary on the Umtata event of December 1998 is given . The aim with these case studies was to see which synoptic, mesoscale, model and radar characteristics could be identified to in dicate severe weather and/or tornado possibilities. Knowledge of these indicators can help operational forecasters to know what to loo k for in future severe weather events in order to forecast with greater accuracy. Reasonable success was achieved through the use of model data fields to “see” tornado signatures or at the very least indicators of severe weather conditions. With the aid of rea l-time radar to monitor the development of the severe storms (in two of the cases) it was possible to identify the tornado cloud struc ture. Without radar coverage not much can be said about these kinds of events.