  Ground-based sky cameras (popularly known as Whole Sky Imagers) are
increasingly used now-a-days for continuous monitoring of the atmosphere. These
imagers have higher temporal and spatial resolutions compared to conventional
satellite images. In this paper, we use ground-based sky cameras to detect the
onset of rainfall. These images contain additional information about cloud
coverage and movement and are therefore useful for accurate rainfall nowcast.
We validate our results using rain gauge measurement recordings and achieve an
accuracy of 89% for correct detection of rainfall onset.
