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. With one of the scientific aims of forecasting evaluations being to concentrate on areas of under-performance, these statistics show that a better observation network would improve conditions for evaluation of forecasts. Further research should be focused on alternative or better techniques to forecast precipitation (general and severe)with greater accuracy.


WaterSA Vol.27(4) 2001: 489-498