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How Clouds Form To understand how clouds form, we need to take a step back and examine the processes of evaporation and condensation. Picture a birdbath outside on a hot day. When the temperature of the environment is warm, molecules of water (H2O) are energetic and can move more, expanding the distances between them. More molecules will leave the birdbath's mass of liquid and become water vapor in the air. On a cool day, the molecules have less energy and are less able to separate themselves from the larger mass of water. (On a very cold day, water molecules generally contract into their solid form, ice, and don't have the level of heat energy needed to separate themselves.) You can see the processes occurring in the first two cases. However, the first scenario's result is net evaporation; and the second scenario's result is net condensation. Other factors can affect these outcomes, but for our purposes, we'll just focus on temperature. Stephen Studd/Stone/Getty Images Clouds get their moisture from a variety of sources, including evaporated ocean water. As water molecules shift between vapor, liquid and solid phases, they move throughout the air, even if we can't see them. However, when a parcel of air cools quickly and reaches saturation, there's a chance water vapor will condense and appear as a cloud. This could occur because of different factors, like a mountain pushing it upwards into cooler air, or perhaps, because it enters a cold front. Additionally, cloud formation happens easily when water vapor has something to cling to, allowing the water vapor to change into its liquid or solid phases. A number of particles can act in this function. Commonly called condensation nuclei or freezing nuclei, these particles become the center of a water droplet or ice crystal. Typically, these will be things like dust particles, sea salt particles and soot from wildfires, and the water droplets or ice crystals form around them. Clouds are, in essence, massive collections of tiny water droplets and crystallized water molecules. The different shapes, textures and other features of clouds depend largely on the conditions under which they form and later develop. For instance, temperature, humidity and altitude are all factors that affect cloud formation. Clouds and Precipitation Clusters of water droplets (called cloud droplets) and crystallized frozen water (called ice crystals or snow crystals) form clouds. A cloud can contain both of these, depending on its temperature. For instance, a cloud's top may be cooler than the lower regions, creating a mix of liquid and frozen water. Gravity causes all the liquid water to fall as rain. The average size and volume of a cloud droplet is tiny, but, if a cloud droplet manages to attract enough water, the influence of gravity causes it to become a raindrop and fall. David James/Riser/Getty Images Cumulonimbus clouds often mean severe thunderstorms and other serious weather. That being said, snow happens a lot like rain. As snow crystals condense and clump together, snowflakes form. When they reach the point where they're too heavy to remain aloft, they fall together as snow. Different surrounding temperatures affect what type of snowflakes will develop. Sometimes on the way down, snowflakes melt into rain; other times they fall intact. Photo courtesy Kenneth G. Libbrecht and SnowCrystals.com A photograph of a snowflake, taken with a special photomicroscope. You may be asking, "If water droplets and snow crystals make up clouds, how do we get hail, sleet and freezing rain?" The answer is that once cloud droplets and ice crystals condense and reach critical falling mass, a few additional processes can occur. Freezing rain, also known as glaze, can occur where warm and cold air fronts meet. A snowflake can fall into cold air, then pass through a layer of warmer air and melt. As it continues to fall and right before it hits, the snowflake passes through a layer of cold air and becomes supercooled. This means that it won't refreeze, but upon impact with a cold object, such as the street or a tree branch, it will immediately turn to ice. Sleet starts the same way as freezing rain, but the melted snowflakes have time to refreeze before they hit the ground. Hail forms during severe storms. The gusty updrafts produced by high winds may knock snowflakes and raindrops up and down until the supercooled water droplets collect themselves into chunks of ice. This can happen repeatedly, until the heavy hail can no longer be lifted by the storm's powerful updrafts. The resulting ice chunks can be quite large when they're finally released and create quite an impact if they hit objects like the hood of your car. Homework IN PENCIL, fill in a line on your summary table with “Clouds Reading”. There were two main sections in this article, “How Clouds Form” and “Clouds and Precipitation”. Write a main point IN PENCIL for each section, and complete the rest of the row IN PENCIL.