Have you ever spent the afternoon lazing in the grass, watching the clouds go by? Have you ever looked into the sky and seen clouds resembling dragons or birds?
Clouds are a part of our sky every day, but you might not know that every cloud tells a story.
Clouds aren’t formed willy-nilly. There are a lot of factors that make clouds appear as they do. Every different shape and size of cloud can tell you a lot about the weather if you know what to look for.
Here we’ll discuss the “King of All Clouds” – the cumulonimbus cloud, also known as thundercloud.
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What are Cumulonimbus Clouds?
The Latin cumulus means “heap,” and nimbus means “rain cloud.” Cumulonimbus clouds (Cb) are commonly known as thunderstorm clouds. They are clouds with vertical growth, like cumulus clouds (Cu).
But unlike the puffy shapes of cumulus clouds, cumulonimbus are much larger. They are denser and higher, flattening out at the top. They can appear ominous and looming, like a mountain or a tower.
These types of clouds create severe weather. Examples are heavy rain, snowstorms, and even tornadoes. When you see a cumulonimbus cloud, you can be sure that a weather event is on its way.
What Causes Cumulonimbus Clouds to Form?
For a cumulonimbus cloud to form, the right conditions must be met.
The perfect mix of moisture, warmth, and unstable air makes the cloud come together. First, there must be a deep layer of unstable air. Unstable air forms when warm moist air is below cold, dry air.
Second, the air must be moist and warm. They form when the lowest layers of air mass are warmer or more humid than the surrounding air. They will not form if the air is dry and cold. Those conditions are more likely to create cumulus clouds.
Lastly, something has to make moist air rise. This can happen in a few different ways. The first way is by convection. Convection is formed by heating the layer of air closest to the ground.
Another way is due to the rising ground forcing the air upwards (orographic uplift).
Orographic uplift is when the wind hits a mountain or other large geographic feature. It then forces the air mass to rise over the barrier. This causes the warm air to rise above the cooler air, creating an upward lift.
It can also be caused by the mass ascent or a weather front forcing the air upward. A front is a boundary between air masses of different temperatures and humidity levels. The front forces the warm air up into the colder air, forming the cloud.
Species of Cumulonimbus Clouds
Like all other types of clouds, there are different species of cumulonimbus clouds.
Here we see the Cumulonimbus calvus (Cb cal) from the Latin meaning “bald.” In this type, the top of the cloud is puffy like a cumulus cloud. The water droplets at the top of the cloud tower are not frozen and have not formed ice crystals yet.
This is the Cumulonimbus capillatus (Cb cap) from the Latin meaning “having hair.”
Here, the top of the cloud is fibrous but hasn’t formed the typical anvil shape. Water droplets have started to freeze. If you spot this cloud, rain has begun or will begin soon.
Supplementary Features and Accessory Clouds
Supplementary features of clouds give the cloud a specific appearance and function.
Each type of cloud can have more than one supplementary feature attached to it. There are eight supplementary features associated with cumulonimbus clouds.
- Arcus – from the Latin meaning “arch.” This feature is formed along a gust front and is commonly known as shelf clouds. With an arcus cloud, you can expect wind and a drop in temperature. Often known as the “whale’s mouth” in the weather community.
- Cauda (cau) – from the Latin meaning “tail.” This feature is observed attached to the wall cloud of a cumulonimbus. This is a sign of an extremely severe storm.
- Incus (inc) – from the Latin term meaning “anvil.” This feature is only seen in cumulonimbus clouds. The quintessential cumulonimbus cloud accessory and look! The larger the incus is, be prepared for a severe storm.
- Mamma (mam) – from the Latin meaning “breast.” This feature resembles cow udders and is observed on the base of the cloud. These are formed by sinking cold air that forms pouches as they are carried through the warmer air.
- Murus (mur) – from the Latin meaning “wall.” The murus is a dark cloud feature extending from the cumulonimbus cloud’s bottom. It is known as a wall cloud. When combined with a tuba feature, these can form tornadoes.
- Praecipitatio (pra) – from the Latin meaning “fall.” This means that the cloud can give off precipitation that hits the ground. Precipitation includes rain, hail, sleet, snow, etc.
- Tuba (tub) – from the Latin meaning “tube.” This feature is best known as a funnel cloud. When accompanied by a murus cloud, the tuba can turn into a tornado. These features are usually companions to large, rotating cumulonimbus clouds called supercells.
- Virga (vir) – from the Latin meaning “rod.” This feature includes all types of precipitation that evaporate before hitting the ground. It looks like wispy streaks falling out of the clouds. Also called “jellyfish clouds” because the wisps look like tentacles.
Accessory clouds are like supplementary cloud features. But they are not attached to the cloud formation. Depending on the accessory, it can be above, below, or around the parent cloud.
Clouds can have more than one accessory cloud. These are the four accessory clouds associated with cumulonimbus clouds:
- Flumen (flb) – from the Latin meaning “river.” Also known as a beaver tail. A flumen is best described as an inflow band detached from the wall cloud. It is associated with tornados and helps to feed the thunderstorm. Flumen are only found with Cb clouds.
- Pannus (pra) – from the Latin meaning “rag,” known as scud clouds. These accessory clouds sit below the cloud base in ragged tufts.
- Pileus (pil) – from the Latin meaning “cap.” This accessory is a cap cloud that sits atop a growing cloud tower. They are made from ice crystals and will sometimes give a rainbow-like appearance.
Pileus clouds show the main cloud is growing quickly, and a storm is imminent.
- Velum (vel) – from the Latin meaning “veil.” This accessory can be described as a horizontal cloud veil that hovers in the center of the parent cloud. It has an appearance like a hula-hoop.
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Life Cycle of a Cumulonimbus Cloud
Like all clouds, cumulonimbus clouds have a lifecycle.
In the building phase, the warm air builds up, rising as it gathers moisture. As the cloud begins to form, it condenses, warming the air further and continuing to rise. The cloud grows quickly in height, reaching the upper troposphere.
Here, the water droplets begin to freeze, joining together to become larger. As the cloud reaches its top height, it enters the mature phase. In this phase, precipitation begins to fall. The falling precipitation creates cold downdrafts.
The cold downdrafts and warm updrafts create friction within the cloud. This builds up static. The static creates electrical discharge or lightning. The cloud top begins to flatten out, giving the distinct anvil shape.
The cooling of the downdrafts eventually cools the warmth of the updrafts. This is the dissipation phase. The strength of the updrafts fizzles out, causing the cloud to dissipate. This entire process takes about half an hour.
What Are the Effects of Cumulonimbus Clouds?
There are many types of weather associated with cumulonimbus clouds. These include heavy rain, thunderstorms, hail, tornadoes, and snow storms.
These clouds can build quickly and produce torrential rain and lightning. They are often observed in the summer or monsoon season across the Southwest. The larger the cloud, the more severe the storm.
Hector the Convector
Hector the Convector sounds like a cartoon character. Or a video game designed to help teach kids about the weather, but it’s actually a real-life storm cloud. A very special storm cloud!
Hector the Convector is a storm system that occurs every day. It happens around 3 pm from September through March.
Hector forms over the Tiwi Islands off Australia’s North Coast in the Timor Sea. The shape of these islands allows for perfect convection. They create the ideal environment for a consistent storm.
The islands, Bathurst and Melville, sit in such a way that they force the sea air onshore and upward. And voila! A storm is born!
The cold sea breezes hit the warm land. This creates the trigger mechanism needed to produce a cumulonimbus cloud.
During the wet season, this happens like clockwork daily at about 3 pm. Regular storms occur globally during the rainy season. It’s similar to what happens in the Southwest United States during the monsoon season. But Hector is different.
Hector isn’t just a storm every day. It’s the same type of storm and the same intensity. It’s a huge cumulonimbus cloud that dumps torrential rains in the exact same place. Sometimes, it’s two huge clouds. But it’s always in the same location.
Hector was named in World War II by pilots and mariners that were working in the area.
The consistent formation of Hector has led to it being used as a navigational landmark. No other storm system has ever been utilized in such a way.
Can Planes Fly Through Cumulonimbus Clouds?
It is best to not fly through cumulonimbus clouds, and pilots are trained to avoid them as much as possible. This is because of the presence of strong, unpredictable updrafts and downdrafts. These turbulent air pockets can make it impossible to maintain altitude, airspeed, and plane control.
There is also the risk of microbursts within the clouds. These quickly change the direction of wind gusts. These microbursts can push and pull planes into hazardous conditions. These conditions may be beyond the control of the pilot.
Cumulonimbus clouds also have the risk of ice and hail. Flying through clouds that are icing can damage the plane. The ice can block sensors and cause navigation issues.
Ice can build up quickly and lead to engine failure. Hail is not observable on weather radar. This means it isn’t easy to avoid. Hail can cause severe damage to engines, windshields, and navigation equipment.
Lightning within the cloud can cause vision impairment and disorientation. It can also damage electrical equipment, navigation, and communication systems.
Tornadoes can also be present in the cumulonimbus cloud. These severe wind tunnels are destructive and must be avoided.
Avoiding the cumulonimbus cloud is the best course of action when flying. If not able to avoid it completely, pilots should “remain on the upwind side of a cumulonimbus cloud and to remain clear of it by at least 20 nautical miles.” 20 nautical miles is equal to 23.02 miles (37.04 km).
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Fun Facts about Cumulonimbus
- The troposphere is the lowest layer of Earth’s atmosphere. All the weather we experience happens in this layer. Cumulonimbus clouds can grow as tall as this layer, spreading across the top.
- Cumulonimbus clouds are the only clouds that can have cauda, flumen, murus, or incus features attached to them.
- Cumulonimbus clouds are the largest cloud formations, sometimes breaking through into the stratosphere.
- Cumulonimbus flammagenitus cloud (CbFg) is also known as the pyrocumulonimbus cloud. This rare type of Cb forms above a massive heat source, like a wildfire.
- Cumulonimbus clouds are one of only two clouds that form vertically.
- Cumulonimbus clouds can extend through all three levels of clouds: low, middle, and high. They are the only clouds that do this.
How long do cumulonimbus storms last?
Cumulonimbus clouds generally last about 20 to 30 minutes before they dissipate. But the storms can go on much longer.
How high is a cumulonimbus cloud?
Cumulonimbus clouds form at an altitude of 1,100 to 6,500 ft (335.28 to 1981.2 m). They can extend well past the flying altitude of 30,000 ft (9144 m). Some cumulonimbus clouds have reached heights of 69,000 ft (21,000 m) or more!