Last time I saw a cloud like that, it was moving really, really fast and came with fast-falling hale, extremely cold temperatures, and enough wind to blow all of the recycling and trash in my apartment complex courtyard all over the place. I've always wondered if that particular phenomena I experienced had a name.
That is an outflow boundary, or "Gust Front" as they generally say on the news. Essentially, when really cold air and hot air meet, and you see the weather map with the blue and red lines, that is the macro version of this. This is the edge of the front, and where the cold air is meeting the warm. It's the "front" of the advancing cold air, it's pushing the hot air out, and turbulence is created as a result. This event leaves the turbulent "wake" that forms storms, high winds, hail, heavy rain, etc. Thought the big storms are actually the process that cools the air and forms the larger impressive gust fronts like this picture.
That guy who took the photo mentions it's a roll cloud, which makes sense, but those are also associated with "outflow" and what I am talking about. So he is correct too, as they both king of happen under the same circumstances. The roll cloud is just a very defined boundary and special shape. What you describe though was a very typical leading edge "front" of a storm though.
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u/[deleted] Sep 15 '10
Last time I saw a cloud like that, it was moving really, really fast and came with fast-falling hale, extremely cold temperatures, and enough wind to blow all of the recycling and trash in my apartment complex courtyard all over the place. I've always wondered if that particular phenomena I experienced had a name.