A cumulonimbus cloud over eastern Georgia photographed on August 9, 2024
Marshall Shepherd
Even on calm nights out for dinner with my wife, the weather phenomenon can find its way to the surface. Friday was one of those evenings. The Italian restaurant was packed, so I left my wife to get us on the waiting list. As I parked the car, I took out my phone camera and snapped a picture of the cumulonimbus cloud above. There are several textbook features associated with it. As such, it became the subject of my latest Meteorology “101” series.
I spotted the cloud while driving and secretly hoped that my vantage point at the restaurant would be optimal for a photo. Naturally, my wife gave me a serious eye roll when I walked in. She said, “OMG, you were there taking pictures.” After twenty-six years of marriage, she is somewhat used to these weather messes. Let’s dive into this cumulonimbus cloud.
The location of the storm relative to the location of the writer who took the photo.
Marshall Shepherd via Radarscope
The storm was located approximately 35 miles southwest of my location in Snellville, Georgia. It was a classic cumulonimbus cloud in many ways. In fact, if you look at the chart below, the picture resembles the symbol for a cumulonimbus (Cb) that has an anvil shape at the top. By definition, the UK Met Office website describes cumulonimbus clouds as: “Menacing-looking multi-level clouds that extend high into the sky in towers or plumes… commonly known as thunderclouds, cumulonimbus is the only type of cloud that can produce hail, thunder and lightning.” The dictionary of the American Meteorological Association officially defines cumulonimbus as, “A major type of cloud (cloud genus), extremely dense and vertically developed, appearing either as isolated clouds or as a line or wall of clouds with separate tops .
Choose cloud abbreviations and descriptions.
NOAA
How are they formed? They represent atmospheric convection and may be associated with significant instability or surface heating. Under certain conditions, some type of forcing (convective heating, a frontal boundary, a mountain, or some other boundary) can lift the air. If the air above is cooler, then like a hot air balloon, the air pack becomes buoyant and rises. You see this commonly with other types of convective clouds, including cumulus and cumulus congestus. The AMS dictionary goes on to say, “Because of its large vertical size and the magnitude and variety of forces acting in and on it, a cumulonimbus is a vertical cloud factory.” Its vertical extent also indicates that there are very strong uplifts.
A nearly vertical view of a thunderstorm over South America as photographed by Apollo 9 … [+] the spacecraft during its earth-orbital mission. (Photo by © CORBIS/Corbis via Getty Images)
Corbis via Getty Images
Let’s go back to my photo at the beginning of the article. Do you see the cauliflower-shaped clouds surrounded at the top by a broad fan-shaped cloud feature? This is the anvil. The anvil shape occurs because as clouds reach the tropopause, a relatively stable area that acts as an atmospheric “cap,” they fan out horizontally. There is something else going on in my picture. In the center, clouds lie above the anvil. When a meteorologist like me sees this, we know that there is a very strong upwelling with a lot of energy that “crosses” the tropopause. Anvils and overpass tops are usually visible on satellite images as well. How much energy can these powerful storms contain? The UK Met Office website writes: “They grow taller and taller until they represent huge power stations, storing the same amount of energy as 10 Hiroshima-sized atomic bombs.”
Atmospheric layers and the extent of some types of clouds.
NOAA
I want to draw your attention to the last feature in my picture. There is a smaller “cap like” cloud over the top of the flyover. It is called a pileus cloud. Such clouds are defined by the International Cloud Atlas as, “An additional cloud of small horizontal extent, in the form of a cap or hood over or attached to the top of a cumulus cloud that often penetrates it.” They can be quite small or quite wide. They form because the air is rising so fast that the water vapor is rapidly turning into an ice cloud. Because these clouds contain ice, rainbows (or bright rainbow colors) can occur.
There are actually different types of cumulonimbus clouds. If you want to take your weather snobbery up a notch at your next dinner party, you might ask what the differences are between cumulonimbus calvus (bloated, water droplets on top), cumulonimbus capillatus (fibrous appearance, a bit frosty) and cumulonimbus incus (anvil). or “incus”, fibrous).
TOPSHOT – A cumulonimbus cloud is seen over the Bangkok skyline on July 28, 2020. (Photo by Mladen … [+] ANTONOV/AFP) (Photo by MLADEN ANTONOV/AFP via Getty Images)
AFP via Getty Images