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Types of storm clouds: which clouds should concern me?

This is a shelf cloud, an indicator of a severe thunderstorm.
This is a shelf cloud, an indicator of a severe thunderstorm.(NWS)
Published: May. 27, 2021 at 3:22 PM EDT|Updated: May. 27, 2021 at 3:23 PM EDT
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(WHSV) - Summer time is basically here and with that comes thunderstorms. There are a few types of clouds that stand out with a storm but which ones should I be concerned about?

Mammatus Clouds

Mammatus clouds create a neat and interesting view of the sky. One characteristic that differentiates mammatus clouds from most clouds is the fact that they form with sinking air just like funnel clouds.

Mammatus clouds form at the bottom of the anvil of a cumulonimbus cloud. They often are associated with strong thunderstorms. These forms of clouds happen when the anvil of a cumulonimbus cloud begins to spread out.

When the clouds spread out, warm air begins to trickle upwards into the bottom of the cloud. The bottom of the anvil cloud can then form “pouches” as the air is cooler in these clouds due to the fact they are saturated.

Cold air sinks, therefore parts of the cloud begin to sink as they stay cooler than some other portions of the cloud. This allows for the beautiful pouch pattern to form. These clouds are harmless and indicate that a thunderstorm is weakening.

A pattern of pouches across the sky can create cool looking views
A pattern of pouches across the sky can create cool looking views(NWS)

Shelf Clouds

Shelf clouds are based at the bottom of a thunderstorm cloud. Storms have updrafts and downdrafts. In an updraft, warm air is being pulled upwards to create or sustain a thunderstorm while a downdraft is the cool air that comes down from the cloud.

This will typically create another updraft. As the cool air coming down from the cloud begins to lift, it condenses, forming the shelf cloud. Shelf clouds themselves are harmless but can be an indicator of strong storms. They are the leading edge of these storms.

Shelf clouds can even form before a derecho strikes. If you see a shelf cloud coming your away, it probably means you are about to get hit by a strong thunderstorm.

This cloud is the leading edge of a strong thunderstorm
This cloud is the leading edge of a strong thunderstorm(NWS)

Wall Clouds

Wall clouds are clouds that drop below a regular storm cloud. They are a lowering of a solid deck of clouds and indicate the beginning phase of potential funnel clouds and tornadoes forming.

They are located in the updraft of a cloud. The warm air from the updraft entrains the cold air in the cloud and increases the dew point.

If you do see a wall cloud, look for rotation. If the wall cloud is rotating, that’s when the storm becomes alarming as the potential formation of tornadoes occur.

The wall cloud is the sudden lowering of part of the storm cloud
The wall cloud is the sudden lowering of part of the storm cloud(NWS)

Scud Clouds

Scud clouds can often be confused with tornadoes. Scud clouds form below the storm cloud and are wispy in appearance. Sometimes they can form narrowly, which creates confusion and can be mistaken as a tornado.

While they are harmless, they do form with strong thunderstorms. Scud clouds can form as a warmer and more moist updraft occurs relatively close to the ground. The air condenses before reaching the cloud and forms the wispy, loose clouds.

Scud clouds are very commonly found on the leading edge of a storm. Scud clouds can also form when an updraft pulls precipitation cooled air from a downdraft. Scud clouds can move at different speeds than the actual thunderstorm. To double check that the clouds are scud, look for the absence of rotation.

This may look like a tornado but it is not. The cloud is looser.
This may look like a tornado but it is not. The cloud is looser.(NWS)

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