Long Range Shooting - Calling Wind Accurately
June 23, 2017
One challenge we will always face is accurately calling wind. We train ourselves to look at the vegetation or the mirage pattern. We study terrain features and watch how it affects the wind flow around it. While shooting in canyons, we have swirling wind that may change direction many times while the bullet is on its way to the target. This is where the art of long-range shooting shines.
By Todd Hodnett - Photoes by Mark Fingar
When we look at the other side of the equation, we used to shoot DOPE (Data On Previous Engagements), but we have moved past that and now "true" our ballistic computers using the actual flight path of the bullet to recalculate the predictive ballistic algorithm. With this, we now have perfect holds for elevation in just a few rounds. Making the perfect wind call, however, is still the biggest reason we miss.
I've heard that "wind at your position means nothing." I laughed and said, "Wind at your position is the only known you have." Don't ignore that critical part of the equation. Next, look at vegetation and mirage, and then the terrain features and how the wind may be manipulated. Even then, most of the time measuring the wind at my position and then adjusting it for the cosine is about 75 percent of the solution.
Let's look in-depth at each portion of a wind call. First, find its direction. Some shooters look into the wind and say, "I think it is coming from there," but there are better ways. One is finding the boil on the horizon with a spotting scope. Even when wind is blowing, you can find an area in which the mirage has no horizontal direction. You can find wind direction by turning the spotting scope into the wind until you see a boil, and this will show where the wind is coming from. Mirage is hard to find some days and is everywhere on others.
Another way to determine wind direction is by turning a Kestrel sideways into the wind, where it is blowing equally down both sides of the impeller. I usually make it turn in one direction and twist the Kestrel until the impeller stops and turns the other direction and continue this back and forth movement until I can look down the seam of the Kestrel and find the exact wind direction. Next I take a wind reading and adjust my wind value for the cosine, which determines the full value wind effect on the bullet.
My next step is to look along the flight path of the bullet and determine if the wind downrange is running the same direction as the cosine that I started with. This is when I look at the vegetation and watch its direction of movement. The problem with vegetation is that it is notÂ the same worldwide. What the sniper manuals state isn't always accurate as areas vary. If you come to my house where it is a semiarid climate, grass and brush grow tall and very rigid. It may not move much in the wind.
You also must be careful that the wind's direction isn't lying. In flat terrain, the wind direction is easy to determine, but when the wind is exposed to terrain features, it can be difficult to predict. As wind flows around terrain, you may see that wind on the lee side of a hill is decompressing as it flows. This katabatic wind is also what I call "dirty air." ThisÂ air may flow in many directions as it descends. It may even wrap around and flow back against a hillside, and vegetation may appear to move against the
Mirage is the primary source of wind calls. The best place to find this is along the transitions in color on the range. Sharp edges can be great resources for seeing mirage. The horizon is one of the best places. A temperature inversion creates this visual pattern and gives us movement that we associate with wind speed. The biggest problem is that mirage patterns flatten out about 12 mph from full value. This makes it hard to use mirage to accurately determine wind speed in high winds. But even in higher winds, the cosine of the wind from the target line will show us the full wind amount of the actual wind affecting the flight path of the bullet. This means that if the wind is blowing 16 mph from 11 o'clock and is a half value wind, the actual mirage will read as 8 mph. The best way to find mirage is with an optic, but optics focus at one point in space. Let me explain. If I focus on a target at 500 meters,Â and then look and see heavy mirage on a target at 800 meters, I am seeing and calling the mirage at 500 meters even though I am looking at the 800-meter target. One can use this to an advantage when mirage is hard to see when focused on the target.
The way I use a spotting scope is to look in the direction of the target and turn my diopter, or focus ring, until I am focused on an area closer than the target. I try to find mirage at this point. Then I focus on mirage at the target to confirm wind speed while also watchingÂ vegetation movement for direction and speed. If mirage is hard to see at this point, I will push the spotting scope above the target to the horizon to see if I can pick up any mirage there.
Be careful while focusing at farther distances. If you go too far, you can invert the converging ray or flip the direction of the mirage in the optic. Then you must mentally flip the direction, but the speed is still pure. You may even see what looks like a waterfall but is really a boil. Just be careful. Many have thought the wind had switched direction when theÂ real problem was the mirage had flipped direction in the optic itself.
This is probably the most misunderstood portion of the wind call. Engineers built most military ranges specifically to reduce wind. They have level berms and trees lining the sides. Good ranges have winds over 12 mph every day, and the best ranges are the ones that have enough terrain features to manipulate wind flow patterns.
With the terrain features come areas where the wind is compressed from moving up and over terrain. It's called an orographic wind, and it occurs when the wind column is compressed and picks up speed. As the wind column flows off the lee side of the terrain feature, it willÂ decompress into dirty air.
Dirty air isn't much of a problem except when trying to read mirage or vegetation.
We've heard the saying that wind is like water. I say that wind is like water without gravity. A better analogy is to think about what smoke would do. As smoke flows over the lee side of a hill, it slows down and tumbles or eddies, which is more of a rolling motion.
Here's an example: Ever see a bullet strike the ground and the dust plume flow against the direction of the wind call? If so, it may have been caused by the terrain feature spilling air around the location of the target. This is not something to take into account. Ignore the dust and adjust off the initial strike. An orographic wind, on the other hand, may cause us to holdÂ more wind than we feel or see. But the wind column needs to be compressed over a large area, such as a long sloping hill, to have any effect.
Another nice aspect is that terrain features may dictate the direction of the wind. Pay attention to what the terrain is telling you, and if the flight path of the bullet is below the top of the terrain feature, there is a good chance that the flow of the terrain will also show the cosine of the wind. So be cognizant of how the terrain will affect the flow of the windÂ column and therefore the flight path of the bullet.
All aspects of wind are important. Whether it is at your position or halfway to the target, when reading mirage or vegetation, one needs to consider all the information that is available for the shot. It all breaks down into volume (speed), value (cosine) and terrain. Many tools exist to gather the necessary data, but be sure to look at it all, not just one piece of the pie. Break down the wind in a step-by-step approach, and do not take anything for granted. WhenÂ you account for each variable and take your time gathering the necessary information, winds are not that complicated. Good luck!