How does water form ice?

Clouds can contain liquid water at temperatures as low as-35 degrees Fahrenheit (-39 degrees Celsius). When ice crystals form around water droplets, these water droplets will lose moisture. Because water vapor has a slight difference in saturation between ice and water, it is easier to precipitate on ice crystals than water droplets under this condition. When ice crystals absorb water vapor and grow, dehydrated air is compensated by absorbing evaporated water vapor in small water droplets. After a few minutes, each ice crystal freezes to the size of 6,543.8+0,000 water droplets, while the water droplets in the cloud keep shrinking until they disappear.

Larger ice crystals fall down and often collide with slower and smaller ice crystals. A series of reactions make the fragments of original ice particles form new ice crystals. When they melt and get wet in the lower places, these ice crystals gather together to form snowflakes. When it accelerates to 20 miles (32 kilometers) per hour, the snowflake melts and forms raindrops.

The biggest raindrops fall the fastest. In a process called merging, it merges with other small water droplets (in the tropics, sometimes in other places, even if the cloud does not contain ice crystals, the merger of such small water droplets is enough to produce raindrops). When the diameter is about115 inch (0.5 cm), the air resistance will change the raindrops from a tight sphere to a shape similar to a wide hamburger. Eventually, the air resistance will crush the heavy raindrops and make them unable to grow bigger. Never has a cloud been able to drop raindrops like tears.

The weatherman cannot always predict whether it will rain or snow. Snow at high altitude sometimes melts in warm air, but only condenses again near the surface, producing ice particles called rain plus snow or hail. If the temperature of rain drops below zero and remains liquid, supercooled ice rain will be formed. When the ice rain falls on the frozen ground, it will quickly form an ice surface called Song Yu. In this way, only a few degrees of temperature change or hundreds of feet of cold air can turn the inconvenient muddy ground into a dangerous and flat frozen road.