Cumulonimbus clouds are large and can indicate severe weather conditions such as lightning, heavy rain, and strong winds. They form from rising warm air that cools and creates ice at higher elevations, and rain at lower levels. Thunderstorms can occur as a single cloud formation or aligned along a frontal boundary. Cumulonimbus clouds go through a life cycle, with each stage having telltale signs or characteristics. Certain weather conditions can create more dangerous thunderstorms, such as supercellular thunderstorms. As the storm continues, it begins to dissipate, and other types of clouds can indicate the arrival of storms.
A cumulonimbus cloud is one of the largest clouds formed in Earth’s weather patterns. The tall, column-like appearance, often with a flat top, can indicate severe lightning, heavy rain, and strong winds. Storm clouds form from rising warm air that cools and creates ice at higher elevations, or height above the ground, and rain at lower levels. They can also create hail and tornadoes that can cause damage to crops and property, and injury to people and animals.
As the sun warms the ground, air begins to rise into the atmosphere. If there is enough moisture or water vapor, clouds can form. Cumulonimbus formation begins with smaller cumulus clouds, which do not indicate severe weather conditions. If the rising air keeps pushing up, the cumulus clouds can rise to towering cumulus clouds, with heights of tens of thousands of feet or meters. The formation of raindrops releases heat and enough energy can be generated to form an increasingly larger cloud.
When lightning begins to occur, a cumulonimbus cloud has developed and a thunderstorm is now present. Thunderstorms can occur as a single cloud formation, often called an airmass storm or isolated cell. They may also be aligned along a frontal boundary, which is the line between a warmer, wetter air mass and a cooler, drier air system. These storm lines are often called gust line storms and can create severe weather conditions.
Clouds are changing all the time and a cumulonimbus cloud is no exception. They go through a life cycle, with each stage having telltale signs or characteristics. These stages are generally known as development, maturity and dissipation.
A developing cumulonimbus cloud absorbs heat from rising air, with rain and ice forming at different altitudes. As raindrops release more heat, rapidly increasing updrafts of air can form in the cloud system. If enough moisture is carried in and ice builds up or sticks together, hail can form.
Mature cumulonimbus clouds are typically called thunderstorms. Lightning occurs when electricity is produced by the friction of water in the cloud. A towering column-like cloud forms with a flat shape, often called an anvil. Anvil is caused when high-velocity air, called a jet stream, pushes the top of the storm in front of the column.
A mature thunderstorm can produce strong winds from downdrafts of cold air leaving the cloud floor, known as microbursts or gusts of wind. Heavy rains and frequent lightning strikes indicate that a mature storm is brewing. Hail can often be seen in areas in the front of the storm, as accumulated ice crystals become too heavy and fall before the storm.
Certain weather conditions can create more dangerous thunderstorms. A supercellular thunderstorm is a mature cumulonimbus cloud with internal rotation, called a mesocyclone. Air moving in different directions at different altitudes causes the supercell to spin, which can cause tornadoes or high winds. Supercells can be very stable systems and dangerous weather conditions can occur for a long time over long distances.
As the storm continues, rain falls through the cloud, displacing moisture and changing the flow of air. The heat that caused the developing storm to rise quickly is gone and the storm begins to dissipate, with some areas of rain but less wind. The towering cloud structure begins to break up and the cumulonimbus becomes a more uniform cloud layer or disappears.
Other types of clouds can indicate the arrival of storms. Cirrus clouds are very thin layers of high-altitude ice crystals, often called wisps or feather-like clouds. These ice crystals are actually the tops of cumulonimbus clouds some distance away that have been blown forward by high-altitude winds, called a jet stream. Cirrus clouds can be an indication that stormy weather is a day or two away, because the jet stream is moving faster than the storm area.
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