Written by Diana LaBelle and Kennie Leet
When water, either liquid or solid ice, condenses on particles in the atmosphere in large enough amounts to be visible to the eye, these are clouds. Clouds form as air cools and reaches the dew point temperature. Because rising air cools, we tend to associate clouds with rising air and/or cooling. Clouds grow when the amount of condensation exceeds the amount of evaporation, and they dissipate if there is more evaporation than condensation. Clouds appear to change size and shape so easily because they are forming and dissipating right in front of our eyes.
Cloud types are named using the terms: cumulo-, strato-, nimbo-, and cirro-. Cumulo- means heap or pile and these types are generally detached fluffy balls. Strato- refers to a flat, sheet-like structure. Cirro- literally means ‘curl of hair’ and these high, wispy clouds contain ice crystals. Nimbo- refers to rain, so any cloud type that includes a prefix or suffix of nimbo-, is a rain cloud. Stratus also refers to low altitude clouds (up to 6,500 feet). The prefix alto refers to mid-altitude (6,500 – 23,000 feet) and cirrus types are typically found at higher altitudes (> 23,000 feet). By combining the different terms, there are ten basic cloud types: stratus, stratocumulus, cumulus, and nimbostratus at low altitude; altostratus and altocumulus, at mid-altitude; cirrus, cirrocumulus, and cirrostratus at high altitude; cumulonimbus that can stretch from low to high altitudes.
1. Cumulus Clouds
Cumulus clouds are characterized by vertical growth. As unstable air rises, it cools and condenses to form beautiful cumulus clouds. Cumulonimbus clouds are perhaps the most recognized and photographed storm clouds because of the awesome energy they release during a storm and the wide variety of cloud formations within the cloud. Cumulonimbus are large storm clouds and formations can top 50,000 feet. Tornadoes, hail, strong winds and heavy rains are all associated with cumulonimbus clouds.
Strong thunderstorms form anvil-shaped tops on the cumulonimbus cloud. As the air within the updraft reaches the stratosphere, the warming in the stratosphere acts as a cap on vertical growth. The air is forced to spread out away from the updraft, forming the anvil top.
When a cumulus cloud is growing, it is referred to as cumulus congestus. Congestus means to pile up. Clouds piling up so the vertical height exceeds the width of the base of the cloud indicate that the atmosphere is unstable and may produce cumulonimbus clouds and thunderstorms if the cloud growth continues.
John Baumlin’s photograph of a cumulus cloud was taken in Boise, Idaho. The flat terrain and the presence of the farm really demonstrate the scale of cloud and its typical dark, flat underside.
When a stable layer exists in the atmosphere, cumulus clouds have a difficult time growing, these clouds with a wider base compared to their vertical height are known as cumulus humilis clouds. Cumulus humilis clouds are fair weather clouds, indicators of a pleasant day with plenty of sunshine between passing clouds.
Cheryl Utter photographed stratocumulus clouds. Stratocumulus clouds form when the atmosphere is drier and more stable. Some say these tell of a “dull day”—not too much sunshine, not too many clouds, but nothing really interesting either. Think of stratocumulus clouds as though someone took the cumulus humilis cloud and pulled it apart like a cotton ball—they have much less defined bases than their true cumulus cousins, and very little vertical growth.
2. Mammatus Clouds
Mammatus clouds are named for their shape. Mammatus is derived from the Latin mamma (meaning "udder" or "breast"). These clouds are formed at the boundary of two air masses with very different properties, such as when cool moist air sinking into warmer drier air. They are considered a supplementary feature rather than a cloud type in itself. This image of mammatus clouds was captured by Susin Wasilewski.
Mammatus clouds can be indicative of a particularly strong thunderstorm, tornado or other severe weather. Aviators will usually avoid flying near mammatus clouds.
3. Saucer Clouds
Lenticular clouds are often referred to as “saucer clouds” and have been occasionally offered up as evidence of UFOs. These stationary cumulus clouds are very common on leeward sides of prominent mountain ranges and high peaks, where air is forced to rise up and over the mountain. The air develops a wave on the leeward side, with lenticular clouds forming in where the air is rising. If you watch lenticular clouds form in this manner they appear to hover or move slightly, lending to the false identification of a UFO or flying saucer. Bruce Oldfield captured this image of lenticular clouds in Endwell a few years ago.
4. Red Skies
Another example of the sheer power and beauty of cumulonimbus storm cloud, Diana Meyn says her image, taken at Colonial Williamsburg this summer, shows a “combination of a brilliant red sunset mixed with an ominous indigo-colored thunderstorm.”
Have you heard the phrase, “Red sky at night sailors delight. Red sky in the morning, sailors take warning?” Did you know this started as ‘rainbow at night’? Think about when you see a rainbow, in order to see a rainbow, you need to have the sun at your back with the light reflecting within the rain droplet that you are looking at. Here in the continental United States, the westerlies steer most of our weather from west to east. If we see a rainbow at night, the sun is setting in the west and we are looking at rain toward the east, rain that is moving away from us, leaving clear skies and a better day tomorrow. If we see a rainbow in the morning, we must be facing west toward the storm system moving toward us, making for worsening conditions throughout the day. Over the years the saying evolved to red sky at night, but we need to be a little careful with that because particles in the atmosphere, such as those from the ash of volcanic eruptions can cause the sunset to be beautiful colors as well.
5. Halos
Halos can be created by the sunlight or moon light and occur at any position on the sky. Halos form when light passes through ice crystals, usually cirrus or cirrostratus clouds and a low sun provide the perfect recipe for halos. A circular halo is always located at 22 degrees from the center of the moon or sun. If you are lucky to see a double halo, a second outer halo will form at 46 degrees from the center of the light source. This halo image was captured by Teri Franzen during the afternoon of the total solar eclipse of 2017. Teri writes, “The bright sunlight tended to wash out the rainbow colors so I photographed from a spot where I could conceal the sun with a tree and capture more detail.”
6. Contrails and sun dogs
This image taken by Gina Vaughn is of a sun dog alongside some contrails. Sun dogs are also known as false suns. They form to the right and left of the sun along the same horizontal plane as the sun. Only when conditions are perfect do you see both sun dogs, and sometimes a halo as well! In addition to the sun dog, this picture shows contrails. The word contrail is short for condensation trail. Contrails form as ice crystals and particles are emitted from the engines of aircraft. When the atmosphere is stable, contrails will disappear quickly, like the one in the upper left hand corner of the image. When you see contrails like this, expect weather conditions to stay the same over the next 24 hours. When the upper atmosphere is unstable, contrails expand in width and persist for greater lengths of time forming lines across the sky. Here in the Binghamton region, we are beneath several commercial flight paths and often on a clear day, will see many contrails across the sky. Expect conditions to change within 24 hours when contrails do not dissipate.
About the Authors
Diana LaBelle
Diana is the chair of Engineering Technologies Department at SUNY Broome. She loves being in the classroom and lab, and over the years, has taught various topics in engineering, computer science, and math. Her hobbies outside the classroom include spending time with her family hiking, taking pictures and learning about science and nature.
Kennie Leet
Kennie is the Chair of the Physical Sciences Department at SUNY Broome. She has a masters in Environmental Science and Policy from Johns Hopkins with a focus in Remote Sensing. Kennie's undergraduate degree is in Meteorology.
Resource Links
You can find more information, along with some additional great images, on these atmospheric phenomena at these websites.