This calls for research! To refresh my memory about snipers, I returned to a few of the books I've read:
SEAL Team Six: Memoirs of an Elite Navy SEAL Sniper by Howard Wasdin and Stephen Templin
No Easy Day: The Firsthand Account of the Mission That Killed Osama Bin Laden by Mark Owen and Kevin Maurer
American Sniper: The Autobiography of the Most Lethal Sniper in U.S. Military History by the late Chris Kyle, Scott McEwen, and Jim DeFelice. (A new memorial edition of this book will be published in October.)
I was trying to remember the way the snipers in training learned to judge wind speed. For instance, if the wind rustles the leaves in the trees and you can feel the wind on your face, then it's considered a light breeze, and that's about 4-7 miles per hour. That kind of thing. It's something hunters probably know, but unless you're close to nature for one reason or another, you probably don't know this.
Beaufort Wind Force Scale
The Beaufort scale relates wind speed to observed conditions as shown in the example above. Francis Beaufort is credited with the scale, in 1805, but the scale actually was the culmination of the work of many others along the way, including Daniel Defoe who wrote Robinson Crusoe.
Interested? The scale is still used today with some modern additions. Check it out at the Wiki that lists the Beaufort scale from 0 to 12 and you too can judge wind speed by its effect on things around you.
For some real fun, go look at the Wind Map of the United States. Totally fascinating. Click on it to Zoom.
I love learning new things, don't you?