A supercooled water droplet (SCWD) refers to a water droplet that remains in a liquid state despite having a temperature below 0°C. To maintain its liquid state, SCWD must be free of solid particles. However, when it encounters solid particles, it promptly freezes onto them. The process of solidification can be initiated by tiny dust particles suspended in the cloud, leading to the Wegner Bergeron Findeisen process. These solid particle initiators are commonly referred to as freezing nuclei. Freezing of water droplets necessitates the presence of freezing nuclei.

In the atmosphere, there are significantly more SCWD than freezing nuclei. As a result, the prevailing state of water in the atmosphere is typically liquid.