National Geographic News

Sonia Harmon

National Geographic

Published November 15, 2013

It's not something you see every day: a horizontal cloud, vibrant orange and rotating, that's taken over the sky.

But that's just what people got to see online this week after a couple in Timbercreek Canyon, Texas, spotted a "weird-looking cloud" and posted a video of it.

Now questions abound: What is it exactly? And what are the chances you'll get to see one in person?

It's called a "roll cloud," which is a type of arcus cloud—low, horizontal formations typically associated with thunderstorms. Depending on the conditions, a roll cloud "can last for several hours and extend for several hundred miles," said Stephen Corfidi, a meteorologist at the National Oceanic and Atmospheric Administration (NOAA).

The rolling motion is the result of winds changing speed and/or direction at the inversion—when the air temperature reverses from its usual state, resulting in warm air on top of cool air—along which the weather disturbance is traveling. "The 'shear' across the inversion sets up a rolling motion much like that of a rolling pin used in a bakery," said Corfidi.

Whether or not you'll see one depends on a "perfect storm" of conditions, which is hard to predict. But you may have better luck in Australia.

According to Corfidi, the cloud in the video is comparable to a "Morning Glory," a roll cloud seen in the months of September and October over northeast Australia. It tends to appear during well-defined inversions with enough accompanying moisture to form a cloud. That's most likely to happen in the early morning, hence the moniker.

"Roll clouds—sometimes more than one in concentric bands—can also occur on the edges of thunderstorms," said Corfidi. "Especially those that form in areas with strong temperature inversions, as frequently is the case during spring over the Great Plains."

But when there's too much moisture—during a thunderstorm, for example—a roll cloud may be hard to see because it's hidden among other clouds.

Considering all of the above factors, the odds of spotting one in your own backyard are pretty slim. But it never hurts to keep your eye on the sky.

46 comments
Felicia Faulkner
Felicia Faulkner

I was so glad to read this happens at the edge of thunderstorms, because I'm pretty sure that is where I saw it before. I live in Bethlehem, Pa and my balcony apartment over looks the entire western hemisphere. I could see that a storm was coming in from the west. From the storm a cloud (similar but no where close to this) was in front of the storm. It ended up releasing tons of hail. 

stephen fain
stephen fain

I am a commercial fisherman & lived for a time on a sailboat in the northern Gulf of Mexico, near Panama City. I was sailing my boat, alone, coming from Key West &  heading to St. George Island FLA. in 2006-January. I was 12miles or so from my destination on one of the most beautiful days EVER, after 4 days/nights passage. I was towing large diving plugs behind the boat, catching some Grouper for Supper.  I stood up to scan the horizon keeping an eye out for idiots driving boats (a common hazard in Florida). I saw a virtually IDENTICAL cloud headind directly toward me....except, behind MY "Roll Cloud" was the SCARIEST looking Squal-Line & Thunderstorms I have EVER seen...in 35 Years of working and living on the Ocean. I was heading 90*- perpendicular to the front & it stretched in a perfectly straight line, for as far as I could see....in either direction. I started battening down hatches, & 15-20 minutes later it got dark, like someone threw a light-switch.  The wind suddenly veered 180* & a VICIOUS down-draft SLAMMED into the boat, laying my 33' cat-ketch over on her beam-ends...with green water coming over the rails into cockpit. Ten minutes later, I was dis-masted by the worst 30 minute change I have ever seen occur in weather....like the Bering Sea kind of weather...not Gulf of Mexico. I barely kept my boat, & most likely my life that afternoon. This all happened,start to finish, in less than an hour to hour & a half. sea state went from 1-2' up to 6-10' & back down to 2-4' in 2 hours or less. I have tried explaining that wierd cloud to a hundred different friends, all mariners....no-one has said they have seen one. I am SO happy to see this video...Maybe I am NOT crazy after-all!

Robert Vitello
Robert Vitello

I saw one many years ago in Cedar Rapids, Iowa. It was in front of a fast moving squall line. It was an erie shade of green and stretched horizon to horizon. Needless to say, I went for shelter.

Nick Mathios
Nick Mathios

hi im from BETHAL and just last week i saw a roll cloud.it stretched for about 50km. from my home town to secunda (sasol). i will post some photos on the sight .i also never knew what a roll cloud was thanks nat geo.

Francesco Sinibaldi
Francesco Sinibaldi

Souffle de lumière.


Une lueur dans

l'immensité du

ciel cristallin,

une image de

jeunesse quand

l'ombre de la

nuit rappelle

l'émotion d'un

moment de joie.


Francesco Sinibaldi 

Lily Ann Plumb
Lily Ann Plumb

I saw one  while traveling on Interstate 90 just outside of Ritzville, WA last year, didn't have camera and didn't know what it was til now. Awesome shot.

Peter Souza
Peter Souza

The roll cloud is my new friend, it brings joy.

Wladim Ponce
Wladim Ponce

Siempre National Geographic me sorprende con éstas maravillas.

Gracias es un gran esfuerzo y felicitaciones por el cumpleaños.



BL Elmore
BL Elmore

Amazing!  I appreciate the knowledge gained through the explanation of this cloud formation.  As sky photos are what I focus on much of the time, I wish I could have experienced this rarity.  Although, I have been near enough to a tornado that I might have gone in the opposite direction as fast as possible.

Paweł Siwak
Paweł Siwak

This is really rare and amazing phenomenon. Nice example of solitary wave. BTW. Not far cousin of tsunami wave. Many thanks for this video.

Nilufa Nizar
Nilufa Nizar

Never seen any thing like this in my life? so amazing 


Eileen Umhoefer
Eileen Umhoefer

I am amazed at the sky and it's wonderful colorful clouds.  Sorry I have never

seen one of these.  Thank you for putting this on line.

charles wright
charles wright

Don't conditions for creating tornados start like this? Spinning tighter and turning up on end to form a funnel?

Pauline Styles
Pauline Styles

That is amazing! It almost looks like a tornado on its side to me! What would the winds be with this kind of condition, considering there is a storm that created this beautiful "perfect storm" as you stated?? I always watch the skies, but don't have a camera to catch all the wonderful things and frightening things nature has to offer :O) So seeing this through someone elses' eyes is wonderful!!

Paul M.
Paul M.

Thus clear evidence that human monkey gas is killing the powers of the Cosmos!

oisin daly
oisin daly

That's amazing. I've never seen, or ever heard about such phenomenon. It is a truly amazing piece of video fooage

Michael Haskins
Michael Haskins

I had HEARD of roll clouds on the lee (downwind) side of mountain ranges. affiliated with soaring weather - from Wikipedia: http://en.wikipedia.org/wiki/Lee_wave

  • Hydraulic jump induced waves are a type of wave that forms when there exists a lower layer of air which is dense, yet thin relative to the size of the mountain. After flowing over the mountain, a type of shock wave forms at the trough of the flow, and a sharp vertical discontinuity called the hydraulic jump forms which can be several times higher than the mountain. The hydraulic jump is similar to a rotor in that it is very turbulent, yet it is not as spatially localized as a rotor. The hydraulic jump itself acts as an obstruction for the stable layer of air moving above it, thereby triggering wave. Hydraulic jumps can distinguished by their towering roll clouds, and have been observed on the Sierra Nevada range[12] as well as mountain ranges in southern California.

Susan Trocchio
Susan Trocchio

wow . . .  isn't  "mother nature" awesome at times

Linda Beavers
Linda Beavers

I'm glad you posted this, if I saw this over my house in Arizona I probably would have been heading for the basement, if I had one.  Now if I see it I will just enjoy!

Margaret Myers
Margaret Myers

This one cloud that I have never seen before.  Clouds and sunsets and sunrises are just amazing .

Swiftright Right
Swiftright Right

I have seen this twice in my life, once in Michigan and once in AZ. Both times it was pretty amazing. To bad it was before the advent of cell phones with cameras


November Rains
November Rains

Cuz "Someone" up there only does His special effects -- for those who will appreciate His work?  "His Wonders are in the Clouds".  (Psalms somewhere.)  (I think "Someone's" not anything like they painted Him to be.)  (and most of that big book is lies.)

Roll it up like a scroll, baby!!!!


Patty Brown
Patty Brown

It's the aliens playing tricks on us again.  MIB, where are you?

ahmad rasheed
ahmad rasheed

I thought is was happened by a rocket spreading a gas. this is amazing. thank for sharing such a beautiful subject. 


Edina Yylee
Edina Yylee

Saw it as well, was wondering why the clouds lie in a roll. Now I know.

Tess Rogers
Tess Rogers

I saw this a few years ago in Washington, MO and had NO idea what it was! It was moving very quickly in my case, and it was quite honestly a little creepy, I'm so happy to have this old mystery solved now.

stephen fain
stephen fain

Peter Souza, see my post on MY experience with "Roll Clouds" above/below....I GUARANTEE YOU....you could find NO JOY in the brush I had with one!

stephen fain
stephen fain

Yeppp...usually followed by MASSIVE down-draft of FREEZING cold air...Thunder,Lightning, & Rain coming down SIDEWAYS in Gulf of Mexico, anyway.


D Ash
D Ash

@Joyce Morgan   Sunlight, angle, saturated cloud, light refraction, dust(?).

November Rains
November Rains

@ahmad rasheed  NASA or HAARP would LOVE to be able to take credit for this.  But they don't got the skill.  ...and they never will.  She's a beauty alright.

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