Top 10 Rare Cloud Formations

Here’s a collection of what I consider the 10 rarest cloud formations, each accompanied by a brief description. These clouds are listed in no specific order of rarity.

1. Nacreous Clouds

Nacreous clouds, often known as mother-of-pearl clouds, form at altitudes of 15-25 km (9-16 miles) in the stratosphere, well above the clouds of the troposphere. Their iridescent hues are stunning, but they are far rarer and higher up than regular iridescent clouds. These clouds are primarily observed in polar regions, particularly in winter at high latitudes like Scandinavia, Alaska, and Northern Canada, although they can occasionally be seen in other areas. In contrast, lower-level iridescent clouds can appear in various places.

Nacreous clouds glow brilliantly in the sunlight at high altitudes, continuing to shine up to two hours after sunset or just before dawn at ground level. Their strikingly bright iridescent colors, combined with their slow movement compared to lower clouds, make them an unforgettable and distinct sight.

Mammatus clouds are distinctive pouch-shaped formations, representing a rare phenomenon of clouds within descending air. Despite their often menacing appearance, they are harmless and do not signal an impending tornado—a common misconception. In reality, mammatus clouds typically appear after a thunderstorm has passed its peak.

These clouds, often called jellyfish clouds due to their resemblance to jellyfish, form at an altitude of around 17,000 feet. They occur when a surge of moist air from the Gulf Stream gets trapped between layers of dry air. The cloud's top takes on a jellyfish-like shape, while long tentacles, known as 'trailing virga,' form from rain droplets that evaporate before hitting the ground.

Noctilucent Clouds, or Polar Mesospheric Clouds, are an incredibly rare cloud formation that occurs at the edge of space, between 82 km and 102 km above the Earth's surface. These clouds appear to glow, as they reflect sunlight from the opposite side of the Earth during the night, creating their luminous appearance.

A mushroom cloud is a distinctive shape of cloud formed by smoke, condensed water vapor, or debris resulting from a large explosion. While most commonly linked to nuclear explosions, any sufficiently powerful blast can create a similar mushroom-shaped effect. Natural events like volcanic eruptions or meteorite impacts can also produce these dramatic cloud formations.

Mushroom clouds form when a large mass of hot, low-density gases rapidly rises from the ground, creating a Rayleigh-Taylor instability. This causes turbulent vortices to spiral downward along the edges of the rising gas, pulling up smoke and debris in the center to create its characteristic 'stem.' As the gas reaches a point where it is no longer less dense than the surrounding air, it disperses, with the debris scattering and drifting back down (see fallout).

Cirrus Kelvin-Helmholtz clouds appear as slender, horizontal spirals and are one of the most recognizable cloud formations. However, they usually last only a minute or two before dissipating, making them a rare sight.

These clouds typically form at an average altitude of around 16,500 feet.

Lenticular clouds, scientifically known as altocumulus standing lenticularis, are stationary, lens-shaped clouds that form at high altitudes. They typically align perpendicular to the direction of the wind.

When stable, moist air flows over a mountain or mountain range, large-scale standing waves can develop on the leeward side. Lenticular clouds often form at the peaks of these waves. Under certain circumstances, these clouds can appear in long strings, creating a formation referred to as a wave cloud.

A roll cloud is a low, horizontal, tube-shaped arcus cloud typically linked to a thunderstorm's gust front, though it can also signal potential microburst activity. The cool, sinking air from the storm's downdraft spreads out along the ground, creating a gust front at the leading edge. This cool air undercuts the warm air being pulled into the storm's updraft, causing water vapor to condense and form a cloud, which often rolls due to wind shear between the winds above and below.

A shelf cloud is a low, horizontal, wedge-shaped arcus cloud, typically associated with a thunderstorm gust front or sometimes even a cold front in the absence of storms. Unlike a roll cloud, a shelf cloud is attached to the base of the parent cloud (usually a thunderstorm). The outer part of the shelf cloud often shows rising cloud motion, while the underside can appear turbulent, boiling, and wind-torn.

According to the Sapporo Meteorological Observatory, these low-altitude stratocumulus clouds form into long, distinct ribbons when trapped by air currents. While wind patterns often create similar formations in stratocumulus clouds, clear photos of clouds rolled into strips are considered rare, the observatory notes.

Contributor: Adam Winkles

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