Flash flooding from intense rainfall frequently results in major damage and loss of life across Africa. In the Sahel, automatic prediction and warning systems for these events, driven by Mesoscale Convective Systems (MCSs), are limited, and Numerical Weather Prediction (NWP) forecasts continue to have little skill. The ground observation network is also sparse, and very few operational meteorological radars exist to facilitate conventional nowcasting approaches.Focusing on the western Sahel, we present a novel approach for producing probabilistic nowcasts of convective activity out to 6âh ahead, using the current location of observed convection. Convective parts of the MCS, associated with extreme and heavy precipitation, are identified from 16âyears of Meteosat Second Generation thermalâinfrared cloudâtop temperature data, and an offline database of locationâconditioned probabilities calculated. From this database, realâtime nowcasts can be quickly produced with minimal calculation. The nowcasts give the probability of convection occurring within a square neighbourhood surrounding each grid point, accounting for the inherent unpredictability of convection at small scales.Compared to a climatological reference, formal verification approaches show the nowcasts to be skilful at predicting convective activity over the study region, for all times of day and out to the 6âh lead time considered. The nowcasts are also skilful at capturing extreme 24âh rain gauge accumulations over Dakar, Senegal. The nowcast skill peaks in the afternoon, with a minimum in the evening. We find that the optimum neighbourhood size varies with lead time, from 10âkm at the nowcast origin to around 100âkm at a 6âh lead time.This simple and skilful nowcasting method could be highly valuable for operational warnings across West Africa and other regions with longâlived thunderstorms, and help to reduce the impacts from heavy rainfall and flooding.This article is protected by copyright. All rights reserved.