Wind shear: an unseen foe for pilots?

A short-distance variation in wind direction or speed is known as wind shear. It is most frequently linked to significant temperature inversions or density gradients and can happen either horizontally or vertically. At either a high or low altitude, wind shear can happen.

Did you know that wind shear contributes to the genesis of tornadoes? We typically associate the word "wind shear" with aviation. Were you aware that hurricanes can be broken up by wind shear, which weakens them overall? Wind shear also aids in the top-speed rotation of wind turbines.

Wind shear develops when the wind at a specific distance—typically a short distance—changes in direction or speed. There is a range of wind shear in the atmosphere. Strong wind shear contributes to various concerns, including tornado forms and aviation problems. Let's talk about the two main categories of wind shear.

Types of Wind Shear
Vertical Shear
This particular wind shear moves vertically or at varying heights. You may thank vertical wind shear for the conditions that lead to a powerful thunderstorm moving through. In other words, during a vertical shear, the shift in winds at this particular height affects (and sometimes even lessens) the intensity of a thunderstorm. This kind of wind shear can influence both changes in wind speed and direction.

Horizontal Shear
This kind of wind shear occurs over a horizontal distance and typically affects changes in direction. When travelling directly through a front or flying close to steep terrain, an aircraft may experience horizontal wind shear. A front is merely the separation of two air masses in the atmosphere. These air masses may be warm or chilly.

Why Does Wind Shear Occur?

1. Frontal activity.
2. Thunderstorms.
3. Temperature inversions.
4. Surface obstructions.
Frontal Wind Shear

Not every front is accompanied with wind shear. Shear, in actuality, only poses an issue if along fronts with extreme wind gradients. There is no hard and fast rule, as there are with so many weather-related phenomena, but the following indicators point to the possibility of wind shear:
• The front is traveling at a speed of at least 30 knots;
• The temperature differential across the front at the surface is 10 o F (5 o C) or greater.
During the weather briefing, you can check these two things to see if the wind shear is present.
Ask the briefer and be ready for the risk of shear on approach if these conditions are present.
Thunderstorm-Induced Wind Shear
Another unfavorable component of thunderstorms is wind shear. These storms' ferocity and their winds have a long history. Shear-related issues are the two biggest issues outside of actual storm penetration. The "downburst" and the "initial gust" are these. The initial gust is the sudden change and wind acceleration soon before a thunderstorm strikes.

The downburst, another wind issue that was previously stated, is associated with downdraft. A thunderstorm downdraft is very strong and concentrated in one area. At 300 feet AGL, this downdraft has a vertical velocity of more than 720 feet per minute. Even a high-performance Air Force jet has been documented in one instance as having its climb capabilities exceeded by the downburst's strength, which can be greater than those of smaller aircraft.

Although the downburst is typically much closer to the thunderstorm than the first gust, its appearance cannot be predicted with absolute certainty. One indicator is the presence of dust clouds, roll clouds, or heavy rain. Best to stay away from these regions.
Temperature Inversions Cause Wind Shear
Those pilots who have flown over the Southwest, Southern California, or Colorado are accustomed to this weather pattern.
A few hundred feet above the ground, a temperature inversion is caused by overnight cooling. When combined with strong winds from the so-called low-level jet stream, this inversion can cause considerable wind shear close to the ground.

Temperature inversion shears have the annoying tendency to bring gusty winds and the shear plane closer to the ground as the inversion fades. In some parts of the Southwest, surface winds are not unusual to reverse direction by 90 degrees and pick up 20 to 30 knots in a matter of minutes. Undoubtedly, such a change would make a strategy challenging at best.

Wind Shear from Surface obstacles
Hangars or other structures near the runway are typically related to wind shear from surface blockage. A quick shift in wind speed can significantly impact a landing.
Mountains are a different form of surface obstacle that might impact wind shear. Some airfields are near mountain ranges, and the final approach roads are near mountain passes. During the approach, severe localized wind shear might be caused by strong surface winds blowing across these passages. The main issue with such shear is how unpredictable its magnitude or severity might be. Such shear can be anticipated wherever there are significant surface winds.

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