The increasingly widespread use of CSP (concentrated solar power) plants to produce electricity has generated a constant search to improve and optimize final production. These plants are looking for new technologies and methodologies that offer significant, reliable strategies which can be applied to their systems. Clouds are hydrometeors which affect solar radiation, decreasing its value and, consequently, electricity production. Knowing when solar radiation is obstructed by clouds provides useful information to CSP operators to adapt electricity production to the cloud presence, optimizing electricity production processes. As a result of this necessity to study cloud cover, short and medium-term cloudiness forecasting is presented here, where cloudiness is predicted for the following three hours. (C) 2014 Elsevier Ltd. All rights reserved.