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Road Trip Survival: Recognizing Which Clouds Mean Danger

By By Meghan Evans, meteorologist
August 20, 2012, 5:11:41 AM EDT

While everyone hopes for beautiful, sunny weather when going on a road trip, it is crucial to be prepared for severe weather.

Checking weather forecasts and staying alert to any weather-related watches and warnings is extremely important when heading out on the open road. A weather radio is a must.

However, in a severe weather situation, conditions can change rapidly and the weather can turn volatile quickly. Being able to read the clouds for severe weather can help save your life.

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The following is a breakdown of ominous looking clouds and whether there is imminent danger or they are actually benign.


Cumulonimbus Clouds
Rapid vertical growth in these cauliflower looking cumulonimbus clouds show that there is a mature thunderstorm, likely producing heavy rain. Abundant moisture and instability due to cool air aloft and heating at the surface set the stage for cumulonimbus to develop.

A lifting mechanism such as a cold front can help trigger these clouds to form.

Heavy rain, frequent lightning, strong winds and hail can all be threats associated with cumulonimbus clouds.


Scud Clouds
Scud clouds may appear to be ominous as they hang vertically below a cumulonimbus clouds. Sometimes scud clouds are mistaken for funnel clouds (see below).

However, these clouds are benign and non-rotating. They often have a raggedy appearance that sets them apart from funnel clouds.


Shelf Clouds
Shelf clouds often form at the leading edge of a gust front or outflow boundary from a thunderstorm, or strong winds flowing down and outward from a storm.

The outer part of a shelf cloud is often smoother with a notable rising motion exhibited by a tiered look (hence, the name shelf cloud!). Underneath, a turbulent, unsettled appearance is often the case.

A shelf cloud should be seen as a harbinger of strong winds, so take caution.


Wall Clouds
A wall cloud is a cloud that is lowered from a thunderstorm, forming when rapidly rising air causes lower pressure below the storm's main updraft.

"Wall clouds can range from a fraction of a mile up to nearly five miles in diameter," according to the National Weather Service.

Wall clouds that rotate are a warning sign of very violent thunderstorms. They can be an indication that a tornado will touch down within minutes or even within an hour.


Funnel Clouds
A funnel cloud is a rotating column of air (visible due to condensation) that does not reach the ground.

If a funnel cloud reaches all the way to the ground then it is classified as a tornado.

When out on the road, a funnel cloud should be treated as a tornado, since they could touch down.


A tornado is a rotating column of air, reaching all the way to the ground. Strong tornadoes are one of the most destructive forces of nature on a small scale. The strongest of which can level entire towns.

A roaring noise, often compared to that of a train, can be heard in many cases when a tornado touches down.

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Thunderstorm Anvil Clouds
Anvil clouds are the flat top of a thunderstorm, or cumulonimbus cloud.

Anvils can spread up to "hundreds of miles downwind from the thunderstorm itself," according to the National Weather Service.

Lightning can strike from anvil clouds, even far away from a thunderstorm. Lightning described as striking "from out of the blue" is usually from an anvil cloud that has drifted from a thunderstorm.

Striking mammatus clouds can sometimes be seen below thunderstorm anvil clouds.


Mammatus Clouds
The rounded and smooth look of mammutus clouds captivate onlookers. They are often found underneath anvil clouds of severe thunderstorms; however, they can form underneath clouds associated with non-severe thunderstorms as well.

It takes a turbulent atmosphere for these clouds to develop.


Asperatus Clouds
Asperatus clouds are very ominous in appearance, usually described as looking like a rough sea.

An abundance of heat in the atmosphere is needed to produce enough energy for the dramatic, rolling formations of asperatus clouds. Another factor is the interaction of very moist air (often on the fringes of thunderstorm complexes) with very dry air.

The darkness of the clouds is likely due to the large amount of water vapor.

Asperatus clouds are not necessarily accompanied by stormy weather. In fact, they have often been observed without the development of thunderstorms.

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