8 Bizarre Cloud Types and Their Meanings

Delicate cirrus clouds or whimsically fluffy cumulus clouds are charming enough on their own. But every now and then, you'll see a formation that eerily resembles a UFO, a crashing ocean wave, or a pale version of the smoke monster from 'Lost.' These rare cloud formations have names too. Keep reading to discover what they’re called, why they form, and what they might mean for your afternoon picnic plans.

1. Lenticular Cloud

True to their name, lenticular clouds are lens-shaped and are often likened to UFOs or stacks of pancakes. When strong winds encounter tall structures like mountains or even buildings, the air can be pushed upwards and over the obstacle. As it rises, the air cools, and if it carries enough moisture, it condenses into a flat cloud formation at the top of the wave. Despite appearing to hover motionlessly above a mountain peak, lenticular clouds are in constant motion: As the air descends, it warms and dries out, while the wind continues to feed the cloud with fresh condensed air from the other side.

When a direct wind meets an obstacle, it doesn’t simply return to its straight path after clearing it. 'Imagine taking your grandma's Cadillac over a speed bump — after that, it will continue to go up and down for a while,' explained cloud physicist Patrick Chuang to WIRED. Essentially, the air keeps moving in waves after passing over the obstacle. Lenticular clouds can form at the crest of these waves, which explains why they sometimes appear to be floating above nothing.

2. Fallstreak Hole

The term 'hole punch cloud' for a fallstreak hole is quite fitting, as it resembles a giant hole-puncher mark in the sky. To form one, you need a layer of cirrocumulus (high-altitude) or altocumulus (medium-altitude) clouds filled with 'supercooled' droplets. These droplets remain in liquid form despite being below freezing, as there is nothing solid to help them freeze. However, when a solid object—often ice crystals from an airplane overhead—enters the cloud, all the supercooled droplets around it freeze and fall, creating a hole in the cloud.

3. Kelvin-Helmholtz Cloud

It’s no accident that Kelvin-Helmholtz clouds—named after Lord Kelvin and Hermann Von Helmholtz, who investigated the physics behind them—bear a striking resemblance to ocean waves: Both phenomena occur when the top layer of a substance moves faster than the one beneath it. In clouds, when the upper layer is warmer and less dense than the cooler, denser lower layer, it can move more quickly. This causes an instability at the boundary, which makes the top edge of the lower layer rise and eventually curl over, much like a wave breaking. If you hear a pilot mention Kelvin-Helmholtz clouds while flying, prepare for some turbulence.

4. Roll Cloud

Roll clouds are elongated, low-hanging tubular arcus clouds that can stretch across hundreds of miles. Like Kelvin-Helmholtz clouds, they form when warm air rests above cooler air, a condition known as an inversion, which signals atmospheric instability. This is typically the result of a thunderstorm. Roll clouds are extremely rare, with the only place they consistently appear being Cape York in Australia, where they are called 'Morning Glory clouds.' These clouds don’t always coincide with storms, and the reason they occur so regularly in this area is still somewhat of a mystery. However, scientists believe it’s due to the constant clash between the sea breezes from the Gulf of Carpentaria to the east and from the Coral Sea to the west.

5. Anvil Cloud

When a thunderstorm forms, powerful updrafts of air rise, cool, and create clouds. However, there is a point in the atmosphere, known as the tropopause, where air ceases to cool with altitude. If an updraft is strong enough to reach this height, it can’t go any further, causing the cloud to spread horizontally. This flat-topped formation is called a cumulonimbus incus, or anvil cloud (incus is Latin for 'anvil'). In rare cases, if the updraft is forceful enough to break past the tropopause into the stratosphere, a protruding cloud formation known as an 'overshooting top' may appear above the flat anvil, signaling an especially powerful storm on the way.

6. Asperitas Cloud

In 2008, Gavin Pretor-Pinney, founder of the Cloud Appreciation Society, proposed to the World Meteorological Organization (WMO) that a new classification be added to the International Cloud Atlas for chaotic, rolling cloud waves that don’t follow a clear pattern. Almost ten years later, the WMO agreed, modifying Pretor-Pinney’s suggested name—asperatus, which means 'roughened' in Latin—to asperitas, the noun form meaning 'roughness.' These clouds appear when stable, horizontal cloud formations at middle to low altitudes are disturbed from multiple directions, often due to an approaching storm.

“Imagine jumping into a pool. When you hit the water, waves—or a splash—expand outward in circles,” meteorologist Matthew Cappucci explained for The Washington Post. “This is similar to how air pockets in the atmosphere move up or down, creating gravity waves near thunderstorms. However, if multiple people were to jump into the pool at the same time, the resulting chaotic, wavelike motions would turn the water’s surface into turmoil.”

7. Nacreous Cloud

If you miss the Northern Lights during your Arctic adventure, nacreous clouds—also called mother-of-pearl clouds—are likely the next best spectacle. These clouds are a type of polar stratospheric cloud, forming in the stratosphere when temperatures plummet well below freezing. For nacreous clouds, that means a chilling -180°F or colder, so they are typically found in the Arctic and Antarctic regions. The ice crystals within these clouds bend light waves, resulting in a stunning array of colors across the sky.

While they are a beautiful sight, nacreous clouds spell trouble for the environment. Studies have shown that polar stratospheric clouds trigger the release of chlorine from compounds like chlorofluorocarbons (CFCs)—synthetic greenhouse gases once commonly used in refrigerants, aerosols, and cleaning agents. This chlorine damages the ozone layer, which is an essential part of the stratosphere.

8. Mammatus Cloud

Mammatus clouds, named after the Latin word ‘mamma’, meaning ‘breast’ or ‘udder’, share a common trait with many other cloud types on this list: they thrive in unstable atmospheric conditions and often emerge around storms. Though scientists continue to debate the exact cause of their formation, one theory suggests it involves sublimation—the process in which ice transforms directly into water vapor without first becoming liquid. In this scenario, ice crystals within a cloud turn into vapor, cooling the surrounding air, which then becomes denser and sinks in pockets. While most often observed beneath storm clouds after intense weather, mammatus clouds can also form from fair-weather clouds like cirrus or altocumulus.