“Bubble clouds” present a striking atmospheric display. These formations can spark curiosity in observers, prompting questions about their nature and what they might signify for the weather. Their distinct visual characteristics set them apart from more common cloud types.
Identifying Bubble Clouds
These formations are officially known as Mammatus clouds, a term derived from the Latin word “mamma,” meaning udder or breast. They are characterized by a cellular pattern of bulbous, pouch-like protrusions that hang from the underside of a larger cloud. These lobes can appear smooth, ragged, or lumpy, varying in size and opacity, and often extend over significant distances.
Mammatus clouds most frequently appear attached to the base of cumulonimbus clouds, which are large thunderstorm clouds. However, they can also form beneath other cloud types, such as altostratus, stratocumulus, and even cirrus clouds, though this is less common. Their visual impact is often enhanced during sunrise or sunset when the low-angle sunlight illuminates their shapes.
How Bubble Clouds Form
The formation of Mammatus clouds involves a process distinct from that of most clouds. Instead, these structures develop from sinking air parcels within a cloud. This occurs when cold, moist air descends from the main cloud body into warmer, drier air below.
As these colder air parcels sink, they cool the surrounding air. The moisture within these descending pockets condenses or sublimates, forming the rounded pouches. A sharp temperature inversion often exists below the cloud base, trapping the cooler, sinking air and contributing to the distinct, bulging shapes. Turbulence within the parent cloud also plays a role in creating the uneven cloud base from which Mammatus can emerge.
What Bubble Clouds Signify
Mammatus clouds are frequently associated with strong, mature thunderstorms, and their presence indicates significant atmospheric instability. While their appearance is striking, they do not directly predict the immediate onset of severe weather like tornadoes. Instead, these clouds typically form during or after the most intense phase of a thunderstorm, or as it begins to dissipate.
Their formation is a visual indicator of powerful atmospheric dynamics: strong sinking air within the storm system. Observing Mammatus clouds suggests that a powerful storm has recently occurred or is nearby, and they can be associated with hail, heavy rain, and lightning. Pilots are cautioned to avoid areas with Mammatus clouds due to convectively induced turbulence. Therefore, while they are a consequence of severe weather conditions, they are generally not a direct warning sign for an immediate surface threat.