The occurrence of low rainfall in semi-arid areas including Dodoma urban leads to a shortage of water. This paper addresses the evaluation of rainfall extreme characteristics by analyzing the variability indices, probability distribution and return periods. The daily rainfall index shown the magnitude of rainfall varied unpredictably within annual wetted days. The study area experienced a period of one to two months per year with extreme seasonality as evaluated using the rainfall seasonality index. The standardized anomaly index indicated the equivalent of 60% of 20 years experienced the dried years with unpredicted occurrence. The Weibull distribution was selected out of Fifteen probability functions when ranked using Kolmogorov-Smirnov and Anderson-Darling tests. The return periods of rainfall had an average rainfall of 576 mm and were predicted using seventeen plotting position methods and Weibull distribution. Therefore, the magnitude of rainfall in the semi-arid areas would not easily be estimated but using more than one technique would improve the evaluation of rainfall characteristics.