Wind impacts the horizontal plane along the bullet flight path while air density and gravity impacts elevation. In rare topographic cases wind may impact the vertical plane such as when shooting up into a narrow canyon. The first step is to determine the wind direction; the angle of the wind to the path of the bullet will either have a major impact on the travel of the bullet or a minor impact depending on its speed and  wind direction. The origin or angle of the wind is expressed in “values.” A full value wind is a 90-degree wind blowing either ‘right to left’ or ‘left to right’ from the shooting position of the rifleman to the target. A half value wind blowing at 45 degrees has half the impact on a bullet than a full value wind, and a 30-degree wind has a third of the value of a full impact wind. As an example, if you have a 10 mph wind blowing across the range of fire at 90 degrees, the windage adjustment will be greater than the same speed wind from a 45or 30-degree direction. If you have a 10 MPH full value wind and a range of 500 yards the bullet will push off course by 18 inches and the adjustment needed is about 3.4 MOA for a 175 grain bullet while a half value wind will only blow the bullet off course by 9 inches and the MOA adjustment is 1.7

There are three basic ways to determine speed and direction, without the expense of a handheld weather station:

1. The way the wind is causing foliage to move.
2. The direction and angle of the flags on the shooting range.
3. By reading the wave patterns contain in a mirage.

Wind Values

To compensate for wind pushing (most times called deflecting) the bullet left of right, the value of the wind needs to be determined. As stated above we define wind as a full value, third value, or a half value wind. A 90-degree wind (a wind directly traveling on a straight line right to left or left to right) is a full value wind. A full value wind has the largest impact of how much a bullet will drift. It is helpful to think in terms of a clock to determine whether a wind is full value or some other value. A full value wind is a wind blowing from 9:00 to 3:00 or vice versa. A third value wind is a wind blowing from 7:00 to 1:00 and a half value is blowing between 2:00 to 8:00.

See the clock diagram:

90 degrees =full value
60 degrees=. 85 value
45 degrees=. 70 value
30 degrees=. 50 value

You can also determine wind speed by minute of angle (MOA). A 1 MPH wind at full value is a ½ MOA.  For example, if a full value wind is blowing at 8 MPH it is a 4-minute wind. This aids the rifleman in making quicker adjustments to the windage turret. Dividing the target into minutes aids in making the correct windage adjustments.