This morning at about 10:30 am, Amy called me while I was working and told me to “stop what you’re doing, go outside, and look up right now.” Overhead, there was a giant, tubular cloud rolling overhead, almost like a horizontal tornado. I couldn’t leave work, and I didn’t have my camera; it was very disappointing to not go and photograph this event. Fortunately, my budding photographer son James was standing by and took these pictures.

An Arcus Cloud is a low, horizontal cloud formation associated with the leading edge of thunderstorm outflow, or occasionally with a cold front even in the absence of thunderstorms. Depending on the shape they take, they are further classified as Roll or Shelf Clouds. This, I assume, was a Roll Cloud.

According to the Cloud Appreciation Society, these happen when vertical columns of warmer air surge up the middle of storm clouds, while cooler air sinks downwards around them, sometimes, though not always (as was the case this morning), proceeding a thunderstorm, heavy rain, and hail. In certain conditions, this sinking air can hit the ground in such a violent way that it causes a solitary wave of air to advance ahead of the storm. In the middle of this advancing wave of air, a roll cloud can occasionally appear, rotating as it travels.

I did not know this before now, but apparently there is a famous roll cloud called the Morning Glory Cloud, that reliably forms at the end of September and beginning of October every year over the northern outback of Australia. This rolling, windy cloud formation is to glider pilots what the Great Barrier Reef is to divers, and many go there to “cloud surf.”

Here are more pictures of roll clouds, movies of the Morning Glory Cloud, and another site about the same.

Update:

Someone has posted a YouTube video of the same cloud:

And here are pics of the same cloud from the Inky site.