Snow forms when water vapor in the atmosphere cools and changes directly into ice, creating ice crystals that grow and stick together as they fall to the ground as snowflakes. This process requires two main conditions: air temperatures at or below freezing (0°C or 32°F) and sufficient moisture in the air. As individual ice crystals form around tiny particles (like dust) inside clouds, they grow by collecting more water vapor, and collisions between crystals lead to the variety of snowflake shapes. If the falling flakes pass through warmer air, they can melt into rain, sleet, or slush; if they stay in cold air, they remain as snow on the ground. Key points
- Necessary conditions: subfreezing temperatures and adequate atmospheric moisture.
- Ice crystals form around microscopic particles and grow by vapor deposition and aggregation, producing snowflakes with diverse shapes depending on atmospheric conditions such as humidity and temperature gradients.
- Ground and air temperatures below freezing help snow accumulate rather than melt.
If you’d like, I can tailor this explanation to a specific location or season, or add a simple diagrammatic breakdown of the steps from water vapor to snow on the ground.
