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Top 5: Clouds that look like tornadoes, but aren't

By Brent Watts, bwatts@wdbj7.com
Published On: Aug 06 2014 10:16:47 AM EDT
Updated On: Jul 15 2014 01:32:49 PM EDT

Every summer, the social media feeds are full of scary looking clouds (SLC's). Some are often thought to be tornadoes and even reported as such.

In reality, tornadoes are rare on the grand scheme of things and not every storm with a scary looking cloud ends up producing a tornado.

Below are a few clouds that are often mistaken for developing tornadoes.

#1 SCUD CLOUD

 The most common tornado-looking cloud is the SCUD. The SCUD, or scattered cumulus under deck, are fragments of clouds that are unattached to and below a layer of higher clouds, like cumulonimbus clouds.

They often appear out front of the thunderstorm as rain-cooled air clashes with warmer air ahead of the storm. 

The clouds often appear to hang low, and if viewed from a distance, give the appearance of a funnel cloud or even a tornado.  The key is look for any rotation. Scud clouds do not rotate, they simply hang.

 

#2 SHELF CLOUD

A shelf cloud resembles it's name, and appears as a low, horizontal cloud. It is typically curved (or semicircular) in nature.

It is formed when rain-cooled air descends toward the ground, then spreads out after reaching Earth's surface. Warmer air is lifted at the leading edge of the system, and  when the warm, moist air condenses, you see the shelf cloud.

Ahead of the shelf cloud, winds can be quite gusty. 

#3 RAIN SHAFT

A rain shaft is often misinterpreted as a funnel cloud or tornado. A sign of very heavy rain or even hail, the developing rain shafts often have a fuzzy, ragged appearance as they descend.

If a source of dry air is present and the air into which the rain is falling is very warm, then strong, and possibly damaging microbursts are possible.

This rain shaft (left) posted by the National Weather Service in Albuquerque, NM could have easily formed in Southwest Virginia. As they mention in their tweet, if you can't see through the rain shaft, avoid driving through it. The rain, or even hail is coming down so hard, it is obstructing sunlight.

#4 MAMMATUS CLOUDS

 While most clouds form when air rises, Mammatus clouds form in sinking air.  The pouch-like structures are typically found under cumulonimbus (storm) clouds.

They are formed when the sinking air is cooler than the warmer air around it. The cloud also must have a high water or ice content.

They odd-looking clouds can appear threatening, but the sinking air required to make these clouds actually indicates weakening of the storm associated with them. The clouds are often found after the worst of the storm is over. 

Melanie Morris Tweeted this photo of mammatus clouds to us during a June storm over the New River Valley. The same mammatus clouds moved east into Roanoke and even Central Virginia. 

#5 WALL CLOUDS

Of all scary looking clouds, a wall cloud is one that needs to be watched carefully.  It's in these clouds that tornadoes can sometimes form.  Wall clouds extend from the base of cumulonimbus (storm) cloud. Typically, there's no precipitation with them since they form where a storm's updraft enters the cloud.

A rapid change in wind direction with height can sometimes cause the wall cloud to rotate, and in rare instances, funnel clouds and tornadoes extend down from the wall cloud. If you see this type of cloud you would want to look for any rotation, and especially any funnel clouds which protrude out of the cloud.