Application of NCEP medium-range EPS in South Africa: Successes and challenges

Warren Tennant

Prediction Research Scientist - South African Weather Service


The NCEP Ensemble Prediction System (EPS) is used operationally in South Africa for medium-range forecasts up to 14-days ahead. The use of model-generated probability forecasts has a clear benefit to the skill of the 1-7 day forecasts. During the second week of the forecast the EPS is used as a heads-up for possible synoptic-scale events and also for predicting average weather conditions and probability density distributions of some elements such as maximum temperature.

Model forecasts have a seasonally and geographically-dependent precipitation bias which directly affects the probability forecasts. A further problem arises when trying to forecast site-specific precipitation probabilities from model grid-sized probabilities, especially for convective-type precipitation.

These issues of model bias, correction of bias and predictability of different weather elements will be discussed. The suite of products generated from the EPS and its forecaster display system will also be shown.