Morning Glory Clouds

Wired Magazine (a great geek mag which I have read since its very first issue in the early 1990's) did an article last month on "Morning Glory Clouds" showing this photo from Australia by Mick Petroff:

You can see more cool pics of these on Google. If you think you've seen one of these, you probably haven't because these particular clouds are fairly rare, from what I can tell. But you may have seen something similar - a shelf cloud, which are common with thunderstorms (Glories appear during fair weather conditions). Wikipedia clarifies that Arcus clouds include Roll clouds (which include Glories) and Shelf clouds. What the precise difference between a roll cloud and a morning glory, it's not clear.

This is the best picture of a shelf cloud that I've ever taken:

You can see more shelf cloud pictures on our Photo Gallery. And of course you may remember the Delaware Mystery Cloud from last year that some people thought was a waterspout, but I believe was an arcus cloud on its end.

WikiPedia says that meteorologists aren't sure exactly how Glories form but they require a sea-breeze and can be sparked by a passing front. The particulars are the mystery -- generally clouds form where humidity is high enough, and this can happen because air is rising and becoming more humid. This can be in one cloud, moving along, or in the case of a lenticular cloud (which glories resemble) the cloud itself is continually reforming itself as air moves through it.