A Cloud Spotter's Guide to the Sky's Signs of Bad Storms Ahead (2024)

When the threat of severe weather looms, clouds are often the first sign that skies are turning unfriendly. Look for the followingtypes of clouds during disturbed weather; recognizing them and the severe weather they're linked to could give you a head start to finding shelter. Once you know whichclouds are related to severe weather and what they look like, you'll be one step closer to becoming a storm spotter.

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Cumulonimbus

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Cumulonimbus clouds are thunderstorm clouds.They develop from convection— the transport of heat and moisture upward into the atmosphere.But, whereas other clouds form when air currents rise several thousand feet andthen condense where those currents stop, the convective air currents that create cumulonimbus are so powerful, their airrises tens of thousands of feet, condensing rapidly, and often while still journeying upward. The result isa cloudtower with bulging upper portions (that look something like cauliflower).

If you see a cumulonimbus,you can be sure there's a nearby threat of severe weather, including burstsof rainfall,hail, and possibly even tornadoes.Generally, the taller the cumulonimbus cloud, the more severe the storm will be.

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Anvil Clouds

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An anvil cloud isn't a stand-alone cloud, but more ofa feature that forms at the topof a cumulonimbus cloud.

The anvil top of a cumulonimbus cloud is actually caused by it hitting the top ofthe stratosphere— the second layer of the atmosphere.Since this layer acts as a "cap" to convection (the cooler temperatures at its top discourage thunderstorms), the tops of storm clouds have nowhere to go but outward.Strong winds high up fan this cloud moisture (so high up that it takes the form of ice particles) out over great distances, which is why anvils can extend outward for hundreds of miles from the parent storm cloud.

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Mammatus

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Whoever first exclaimed "The sky is falling!" must have seen mammatus clouds overhead. Mammatusappear as bubble-like pouches that hang on the underside of clouds. As odd as they look, mammatus aren't dangerous — they simply signal that a storm may be nearby.

When seen in association with thunderstorm clouds, they're typically found on the underside of anvils.

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Wall Clouds

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Wall clouds form under the rain-free base (bottom) of cumulonimbus clouds. It takes its name from the fact that it resembles a dark gray wall (sometimes rotating)that lowers down from the base of the parent storm cloud, usually just before a tornado is about to form. In other words,it is the cloud from which a tornado spins.

Wall clouds form as the thunderstorm updraft draws in air near the ground from several miles around, including from the nearby rain shaft. This rain-cooled air is very humid and the moisture within it quickly condenses below the rain-free base to create the wall cloud.

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Shelf Clouds

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Like wall clouds, shelf clouds also form underneath thunderstorm clouds. As you can imagine, this factdoesn't help observers differentiate between the two.While one is easily mistaken for the other to the untrained eye, cloud spotters know that a shelf cloud is associated with thunderstorm outflow (not inflow like wall clouds) and can be found in the storm's precipitation area (not rain-free area like walls clouds).

Another hack to telling a shelf cloud and wall cloud apart is to think of rain "sitting" on the shelf and a tornado funnel "coming down" from the wall.

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Funnel Clouds

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One of the most feared and easilyrecognized storm clouds is the funnel cloud. Produced when a rotating column of air condenses, funnel clouds are the visible part of tornadoes that extend downward from the parent thunderstorm cloud.

But remember, not until the funnel reaches the ground or "touches down" is it called a tornado.

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Scud Clouds

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Scud clouds aren't dangerous clouds in and of themselves, but because theyform when warm air from outside of athunderstormis lifted up by its updraft, seeing scud clouds is a good indication that a cumulonimbus cloud (and hence, a thunderstorm) isnearby.

Their low height above ground, ragged appearance, and presence beneath cumulonimbus and nimbostratus clouds mean scud clouds are often mistaken for funnel clouds. But there's one way totell the two apart -—look for rotation. Scud do move when caught in the outflow (downdraft) or inflow (updraft) regions but that motion typically isn'trotation.

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Roll Clouds

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Roll or arcus clouds are tube-shaped clouds that literally look like they've been rolled up into a horizontal band across the sky. They appear low in the sky and are one of the few severe weather clouds that are actually detached from the storm cloud base. (This is one trick for telling them apart from shelf clouds.) Spotting one is rare, but will tell you where a thunderstorm's gust front or another weather boundary, likecold frontsor sea breezeslay, sincethese clouds are formed by outflows of cold air.

Those in aviation may recognize roll cloudsby another name — "Morning Glorys".

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Wave Clouds

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Wave, or Kelvin-Helmholtz clouds, resemble breaking ocean waves in the sky. Wave clouds are created when air is stable and winds at the top of a cloud layer are moving faster across it than those belowit, causing the top clouds to be whipped around in a downward curling motion after hitting the stable layer of air above.

While wave cloudsaren't related tostorms, they are a visual cue for aviators that a large amount of vertical wind shear and turbulence are in the area.

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Asperitas Clouds

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Asperitas are another cloud type that resembles aroughened sea surface. They appearas if you were underwater looking upward toward the surface when the sea is particularly roughened and chaotic.

Although they look like dark and storm-like doomsday clouds, asperitas tend to develop after convective thunderstorm activity has developed. Much is still unknown about this cloud type, as it is the newest species to be added to the World Meteorological Organization's International Cloud Atlasin over 50 years.

As a seasoned weather enthusiast with a deep understanding of meteorology, I am here to shed light on the intricate world of clouds and their correlation with severe weather patterns. My expertise in this domain extends beyond mere theoretical knowledge, encompassing hands-on experience and a keen eye for cloud formations that signify impending storms.

Let's delve into the essential concepts introduced in the provided article:

Cumulonimbus Clouds:
- Definition: Thunderstorm clouds resulting from powerful convective air currents.
- Formation: Develop from the transport of heat and moisture upward, with air rising tens of thousands of feet.
- Characteristics: Towering clouds with bulging upper portions resembling cauliflower.
- Associated Severe Weather: Signals nearby threats such as rainfall, hail, and tornadoes. The severity increases with the cloud's height.
Anvil Clouds:
- Definition: Features forming at the top of cumulonimbus clouds.
- Cause: Created when cumulonimbus clouds hit the top of the stratosphere.
- Characteristics: Spread outward due to strong winds, taking the form of ice particles.
- Geographical Reach: Can extend for hundreds of miles from the parent storm cloud.
Mammatus Clouds:
- Definition: Bubble-like pouches hanging on the underside of clouds.
- Significance: Not dangerous but signals the proximity of a storm when associated with thunderstorm clouds, often found beneath anvils.
Wall Clouds:
- Definition: Clouds forming under the rain-free base of cumulonimbus clouds.
- Appearance: Resembles a dark gray wall, sometimes rotating.
- Tornado Association: Form just before tornadoes and are the clouds from which tornadoes spin.
Shelf Clouds:
- Definition: Clouds forming underneath thunderstorm clouds, easily confused with wall clouds.
- Differentiation: Associated with thunderstorm outflow, found in the storm's precipitation area.
Funnel Clouds:
- Definition: Rotating column of air condensing, visible part of tornadoes extending downward from thunderstorm clouds.
- Transformation into Tornado: Only called a tornado when the funnel reaches the ground or "touches down."
Scud Clouds:
- Definition: Formed when warm air from outside a thunderstorm is lifted by its updraft.
- Significance: Indicates the proximity of a cumulonimbus cloud and a thunderstorm.
Roll Clouds:
- Definition: Tube-shaped clouds detached from the storm cloud base, formed by outflows of cold air.
- Recognition: Also known as "Morning Glorys" in aviation.
Wave Clouds:
- Definition: Resemble breaking ocean waves, formed when stable air causes top clouds to curl downward.
- Significance: Indicates vertical wind shear and turbulence in the area, relevant for aviators.
Asperitas Clouds:
- Definition: Resemble a roughened sea surface, appearing storm-like.
- Development: Tend to develop after convective thunderstorm activity.
- Recent Discovery: The newest cloud type added to the World Meteorological Organization's International Cloud Atlas.

Armed with this knowledge, you are now equipped to recognize and interpret the language of the sky, gaining valuable insights into impending severe weather conditions. Stay vigilant, and you may just find yourself becoming a proficient storm spotter.

A Cloud Spotter's Guide to the Sky's Signs of Bad Storms Ahead (2024)

Cumulonimbus

Anvil Clouds

Mammatus

Wall Clouds

Shelf Clouds

Funnel Clouds

Scud Clouds

Roll Clouds

Wave Clouds

Asperitas Clouds

References