Evaluation of ISKA forecast performance : An investigation on binary and probabilistic forecast skill scores

Abstract

The company Ignitia provides rainfall forecasts through SMS to subscribers in Ghana, Mali and some other countries in the West African region south of Sahara. Their ensemble-based probabilistic forecast product iska, based on the high-resolution weather model WRF with modifications, has been developed to better simulate tropical conditions where rainfall is driven by convection.  This external investigation determined the forecast skill of iska by validating against NOAA satellite rainfall product. As comparison, rainfall probability forecasts from the global model GFS and from Weather Underground were evaluated. The iska forecasts outperformed the GFS forecasts and the Weather Underground forecasts in terms of accuracy. The statistical skill decreased towards the Sahel region and also towards the coast, the latter probably an artefact of the NOAA product having problems in identifying local warm-cloud rain, meaning that the forecast skill by the coast might be better than indicated