Methods, systems, and computer program products for determining severity of a geomagnetic disturbance on a power grid using similarity measures are provided herein. A method includes extracting multiple features of activity associated with geomagnetically induced currents from multiple heterogeneous data streams; comparing the extracted features to historical data related to geomagnetically induced currents to determine a level of similarity between each of the extracted features and the historical data; assigning a level of severity to one or more of the extracted features having a level of similarity with the historical data above a given threshold; and generating a notification comprising (i) a prediction of activity associated with geomagnetically induced currents based on the extracted features having a level of similarity with the historical data above the given threshold, and (ii) the level of severity assigned thereto.