Thursday, June 16, 2011

Cloud Streets

Cloud streets are parallel rows of cumulus clouds that line up in the direction of a steady wind.

The lines are typically about five miles apart, with clear sky between, and they can extend for hundreds of miles.

Also called "horizontal convective rolls," they often form over flat country in spring or summer when the wind is blowing beneath an inversion layer. As the wind travels under that layer, it divides into a series of counterrotating cells. Where the air in two adjacent cells lifts upward, a line of clouds forms, and where they join to spin downward, clear air prevails.

Glider pilots can stay aloft for miles by following cloud streets.

Wikipedia on Horizontal Convective Rolls
Photo by Stu Ostro from


Tom Hart said...

As the winner of the South Junior High 7th Grade Weatherman Prize (a rather disappointing mimeographed "certificate"), I really enjoyed this post. Thanks James!

On an art-related note, this (like the earlier article on the "reverse" rays of a setting sun bouncing off of a body of water)makes me ponder the challenges of painting a rare meteorological event - i.e. one that looks "wrong" unless one is familiar with the phenomenon, which - by definition - few people would be. Therefore, when and why would one include such a rare phenomenon in a painting...I wonder "aloud".

James Gurney said...

Hi, Tom, Good question. I guess it depends on the intent of the painting. If it's to produce a conventionally pleasing landscape to sell in a gallery, it might not be a good idea. But to capture the world and all its wonders for your own curiosity (and perhaps that of discerning buyers), why not?

It is true that Nature often presents us with cloud effects that would be confusing or silly in a painting if you copied them exactly. Two equal clouds side by side, for example.

Tom Hart said...

That's a good point Jim: "Why not?"

This post also reminds me how sad it is that we (myself definitely included) don't spend nearly enough time looking at the skies. I'm sure we all did it much more in our younger days (at least I hope so), lying on a lawn on a summer's day...

Gail Sauter said...

Hi James,

Following along this scientific-bent line of posts.... how about looking at water, reflections, refractions and highlights?

James Gurney said...

Gail, I'm sure I'll do more on those topics in future, but if you put "reflections" etc. in the search box on the upper left of the blog, you'll find previous posts on the topic.