Evaluation of short-term weather forecasts in South Africa

Abstract

In this paper a brief overview will be given for the reasons for doing evaluations of short-term weather forecasts as well as the methodology thereof. Short-term weather forecasts are defined as a forecast valid for the current day as well as the next day. In other words up to 48 h ahead. Results are given for South African Weather Service temperature, rainfall and severe weather forecasts as issued by head office in Pretoria. Temperature forecasts generally tend to be accurate to within a limit of 2.3°C. A comparison is made between temperature forecasts for an inland station, a coastal station and a station influenced by the escarpment. Tendencies of rainfall forecasts show that rain is forecast more often than it occurs. Comparative rainfall forecasts for a summer and winter rainfall region are shown. Severe weather events are sometimes captured well, but severe thunderstorms are not predicted with great accuracy. Once again the tendency is to over-forecast.

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