May 30, 2021

The Time of Year You Can See the Air Move

 Most of the time, you can not see the air move.  You can feel it, but the complex, turbulent motions are invisible to you, except when it interacts with leaves and branches on trees and plants.

But for a few weeks of the year, the sky is full of small, cotton-like tuffs that like a natural MRI machine reveals the complex three-dimensional motions of the atmosphere.  

Cottonwood season.  And we right in the middle of it.  

Being cottonwood aware is of particular value this year.  It reveals the active dispersion and movement of air that makes the outdoors essentially COVID safe, and thus should be of some comfort for those nervous about transmission outside.

Cottonwood seeds are embedded in small cotton-like fibers.   A million seeds weigh about 3 pounds.  Yes, each seed and tuff weights about .000003 pounds.   And that fact, plus the cottonwood tuff, means that these seeds fall VERY, VERY, VERY slowly.   So slowly that they are excellent markers for the three-dimensional flow of the air on which they are taking a ride.

Yesterday, I sat back and watched the cottonwood seed show, on a day when the winds were quite light.  It was quite a show and very revealing.

Check out my video below taken Saturday afternoon

Watch the leaves on the trees....they are hardly moving, yet there is substantial air motion.

You can appreciate some of the 3-D motion from this University of Wyoming video:

Watch two seed tuffs over time and you see them separate from each other--that is a visual sign of air dispersion and dilution.

And while you are watching the cottonwood tuffs, take a look around the vicinity of the sun.

We have a high cirrostratus cloud layer over the region and I expect some impressive halos and sun dogs today.   These ice crystal clouds preferentially bend light by 22 degrees, creating a ring around the sun.

At one time, halos and their cousin, sun dogs (bright areas on both sides of the halo) were thought to presage the death of kings or some other terrible events.  

Finally, you might want to find your shorts and tee shirts.  Western Washington is predicted to warm into the lower 80s on Tuesday and Wednesday and the Columbia Basin will see highs in the 100s.    To pre-warm you up, below is the forecast high temperatures for Tuesday at 5 PM.

80s from north Seattle southward and 90s and more over the Columbia Basin.  The coast is cooler and cool it will spread over the Strait of Juan de Fuca with onshore flow.


  1. The largest tree on our property is a cottonwood, over 6 feet in diameter. We have been getting snow for about a week, with small drifts accumulating in various areas at our place. They also have a characteristic odor, which some people like and some people hate. I am not particularly fond of it, but it does not really bother me. But if you have allergies, it is just another thing to cause aggravation. The seeds germinate very quickly and we find numerous starts, including in potted plants.

  2. Loved the micrograph! Good article. Thanks.

  3. Allergy aggravation for sure!...I usually like to leave my screened bedroom window open at night, for the cooler air...but not right now...lots of congestion and sneezing happens!


Please make sure your comments are civil. Name calling and personal attacks are not appropriate.

The Cooling Has Begun

 The differences in temperature between noon today (Wednesday) and yesterday are quite large west of the Cascade crest (see plot below).  So...