A diagram showing the different atmospheric conditions needed for rain, sleet, snow, and freezing rain.
Precipitation is the process through which water falls from the sky, and it comes in many different forms. The form it comes in all depends on the exact atmospheric conditions at that moment. In this article, we will talk about the four most common types of precipitation: sleet, rain, freezing rain, and snow.
Rain
Rain is probably the most familiar form of precipitation for most people. It happens when water droplets in the clouds become too heavy to remain in the air. This leads to them falling to the ground as liquid water. The formation of rain begins with the evaporation of water from oceans, lakes, rivers, etc., which rises into the atmosphere. As this moisture goes up, it cools and condenses around tiny particles in the air, forming clouds. When these droplets within the clouds grow to a big enough size, gravity takes over, and they fall as rain.
Rain varies in intensity from a light drizzle to heavy downpours. Its impact on the environment is also very important; rain refills water supplies and supports plant growth, but it can lead to flooding if the amount of rain is too much. The temperature at ground level plays a crucial role in whether precipitation falls as rain or another form. It all depends, but generally, if the air temperature is above 40°F (4.5°C), the precipitation will definitely fall as rain.
Sleet
Sleet forms when snowflakes fall through a shallow layer of warm air, momentarily melt into raindrops, and then go back into a deep layer of freezing air near the ground. This transition through different temperature layers causes the raindrops to partially or fully freeze before reaching the ground, which creates small ice pellets called sleet. Unlike snow, which is soft, sleet feels hard and bounces upon impact.
Sleet usually occurs during transitional weather events where cold air is replaced by warmer air, or vice versa. This can happen during the change of seasons, especially in early spring or late autumn. Sleet can make roads slippery, similar to freezing rain, but it tends not to stick to surfaces as much because it’s smaller in size and is often a mix of ice and liquid.
Freezing Rain
Freezing rain is probably the most dangerous form of precipitation on this list because it leads to ice accumulation. It forms when snowflakes or raindrops fall through a thick layer of warmer air but then go through a thin, sub-freezing layer of air just above the ground. This means that although freezing rain will fall as liquid water all the way, its temperature will be below 32°F (0°C). As a result, it will freeze upon coming into contact with any sub-freezing object on the ground, leading to a dangerous coating of ice over everything, including roads, trees, and power lines.
The conditions for freezing rain are very specific, requiring a warm layer sandwiched between two cold layers, one layer in the upper atmosphere where snow forms and another layer near the ground. When this ice begins to build up, it causes significant disruptions. Ice from freezing rain is often transparent, giving branches and power lines a glossy appearance, but this beauty is deceptive because it adds a lot of weight, which can cause branches to snap or power lines to fall. Driving conditions can also become hazardous due to freezing rain.
Snow
Finally, snow forms when water vapor in the atmosphere freezes into ice crystals without turning into liquid first. These ice crystals can clump together to form snowflakes, varying in size and shape but all having a hexagonal structure. For snow to reach the ground, the entire path from the cloud it forms in to the ground must be below freezing. Unlike rain, snow accumulates, which can lead to the impacts from snowstorms or blizzards to be severe.