These images show the conversion of cloud droplets and raindrops to ice inside a numerically simulated cumulus cloud. The visible cloud (white or blue) emerges from a turbulent, invisible moist layer in the atmosphere (red). Inside the cloud, also invisible to a human eye, regions where frozen raindrops (pink) and cloud droplets (orange) interact are of interest. Laboratory studies suggest that explosive development of ice crystals can occur in these conditions, at temperatures between -4 and -8 degrees Celsius, and this “rime-splintering” mechanism is often invoked to explain past observations of the rapid development of large numbers of ice crystals in cumuli.