In Part 3 of our How To Read The Wind – The Ultimate Guide series we are delving into wind speed. We discuss ways to measure it with instruments, and some rules of thumb to use as a backup when the instruments fail. While less complex than angle changes, you still need to be cognizant of speed variations. Particularly speed variations at or near full value angles. Small velocity changes at full value can make a big difference at longer distances. Minor changes at angles that are less steep with less influence are less of a concern. The problem with speed changes is you can only accurately measure them at the shooting position. Everywhere else you are observing speed effects and attempting to quantify those effects with an educated guess, but that’s still all it is, a guess.
Wind Reading – Wind Speed
The wind angles are more complicated and complex than measuring speed and speed changes, sometimes anyway! Again I suggest getting in the habit of using a common baseline when running your drop charts. Set everything up to give you wind adjustments for a 90 degree wind angle with a 10mph wind speed. You can take an adjustment that was run on that baseline and work with it. For example if your chart tells you that at 500 yards with a 10mph wind from 90 degrees you need a 0.6 MIL adjustment to compensate for the wind…you can halve that. So if it’s actually a 5mph wind at 90 degrees you can just halve the 0.6 and run 0.3 MILs for adjustment and that works. The opposite is not true, you can’t multiply a 1mph wind adjustment by 10 to get a 10mph value. These adjustments aren’t linear, the wind’s effects are cumulative. So starting with a larger number is a bit more accurate when using it as a baseline or a rule of thumb!
Wind Speed Rules of Thumb
There are many wind speed rules of thumb, I’m going to list a few of them and might throw in a few tips of my own along the way. Again, these aren’t absolutes just a few quick and dirty rules of thumb to help estimate wind speed based on what you are observing of the conditions around you. These tables are known as Beaufort Scales and there are many versions out there. Don’t be afraid to Google them and read several to get a feel for how they work and how close to reality they are, or are not.
- 0mph – Smoke rises straight up, no movement of grass
- 1mph-3mph – Smoke moves in direction of wind, slight movement of grass
- 4mph-7mph – Wind felt lightly on the face *Very Accurate*
- 8mph-12mph – Leaves turn, twigs and treetops will be in motion
- 13mph-18mph – Loose paper, dust, and paper will blow around, small tree branches will move
- 19mph-25mph – Large tree branches move, entire trees will sway if small
- 25mph-30mph – Large branches will be in constant motion and walking against the wind becomes difficult
There is another way to estimate wind speed called the Flag Method. This one is straight out of the US Military Field Manuals and is fairly simple. You look at any flag, cloth, etc. that is flapping in the wind. Estimate the angle of the flag in relation to the flag pole and then divide that number by four for a fairly accurate estimate of the wind speed where the flag is located.
Mirage is a good, field expedient, method for determining wind speed. There are a few significant advantages to using Mirage to estimate wind speed and few, if any, downsides. Mirage is what you see when you look above the pavement in the summer and you see waving lines of heat coming off the ground. The difference in air temperature creates that wavy effect and by interpreting the angle of the lines to the ground and how they are moving, you can get a very functional estimate of the wind speed in the same area.
The best method I’ve heard for reading Mirage is to focus your Rifle Scope or Spotting Scope on the target. Get the image good and crisp. Then dial the focus/parallax knob back a quarter turn. You want to be moving closer in distance toward yourself with the parallax knob. The idea is to focus the image approximately three fourths the distance between the shooting position and the target. Then by interpreting the Mirage you can get an idea of the wind speed. The chart above helps give you an idea what Mirage of different speeds is doing.
There are some special considerations with Mirage that you need to be aware of. For starters, as I just mentioned, do NOT focus the parallax knob beyond the target. If you turn the knob the wrong way the Mirage can flip and give you a completely inaccurate reading about what the wind is doing. Always focus between the firing position and the target. An advantage of working with Mirage is that it gives you a full value picture of what the wind is doing. You don’t have to worry about angles either! If you are observing Mirage in front of your target and it appears to be a 5mph wind, that’s your 5mph full value wind. You don’t need to obsess about the angles. Whichever direction the wind is coming from, you are always observing a full value Mirage.
You may need to watch this full screen to be able to see the mirage!
Another thing to watch for when observing and reading mirage is a shimmer. If the mirage is moving from right to left, steadily, and then it seems to slow down and shimmer left and right, the wind is changing direction. What you are actually observing is the wind angle changing before your eyes. A zero value wind appears as boiling mirage. It moves straight up from the ground. Picture this, that right to left wind is blowing the mirage to the left as it rises off the ground. As the wind angle shifts, the angle of the mirage will tilt from left up to vertical and then to the right if you watch the wind angle change occur. So if you’re watching the mirage move in one direction, and then it shimmers and dances around, wait till the shift finishes before doping the new angle and releasing your shot! If you see this happen, it’s a real zen moment. I’ve used a hold off the left side of a target, observed the shimmer, waited and then basically held off the right side using the same hold after the angle shifted and hit it. Hitting the target twice in a matter of seconds using completely opposing wind holds is pretty neat. Like I said, a zen moment, you feel like you’re starting to figure stuff out when that happens!
A lot of doping the wind speed in your area is experience driven. That means I can write article after article on the how of going out and doping your wind speed but until you actually go out and do it, you won’t learn much. You have to become a student of behavior, specifically the wind’s behavior. Observe what you see happening around you, make a guess as to what it represents, and then use instrumentation like a Kestrel to verify your guess. Remember the scientific method? The idea is to gain experience and calibrate what you are seeing so that it matches what’s really happening by teaching your body how to interpret what you see. In the next segment of our How To Read The Wind – The Ultimate Guide series we’ll be discussing equipment and the effects of terrain on the wind! This is a complex subject, so if you have questions, drop them in the comments below!
Owner and Proprietor of AccuracyTech, LLC. Rich is a Firearms Enthusiast, Precision Rifle Competitor, and Writer. He is committed to bringing readers quality reviews and articles related to the Precision Shooting Sports. If you have any questions for him, please use the contact form on the site.