Weather
Wind shear and turbulence for drone pilots
Wind shear is a sudden change in wind speed or direction over a short distance, and turbulence comes from obstructions, heated ground and shear. Because surface friction slows the wind near the ground, wind at 350 ft is usually stronger than at the launch point, and buildings, ridges and shorelines can make it gusty and unpredictable.
What causes turbulence?
The Aviation Weather Handbook lists three causes: convective currents (convective turbulence), obstructions in the wind flow (mechanical turbulence), and wind shear. Convective turbulence is vertical motion from rising and sinking air, strongest on warm afternoons with light winds. Mechanical turbulence is eddies behind trees, buildings and terrain. Shear turbulence appears where two wind currents of different speed or direction meet.
Sources (checked 2026-11-14): FAA Aviation Weather Handbook (FAA-H-8083-28B, 2026).
What is wind shear?
Wind shear is a sudden, drastic change in wind speed or direction over a small area. It can occur in any direction and at any altitude, and can produce violent updrafts and downdrafts or abrupt shifts in the aircraft's horizontal motion. The study guide and the Handbook both say it can remain undetected, and that it is especially hazardous low to the ground because there is no room to recover.
The Handbook's formal definition of non-convective low-level wind shear (LLWS) is a shear of 10 kt or more per 100 ft in a layer more than 200 ft thick within 2,000 ft of the surface. LLWS is common with passing fronts, temperature inversions and strong upper-level winds greater than 25 kt, and it also appears with sea breeze fronts and lee-side mountain effects. A tailwind that quickly turns into a headwind increases airspeed and performance. A headwind that turns into a tailwind decreases both.
Sources (checked 2026-11-14): FAA Aviation Weather Handbook (FAA-H-8083-28B, 2026); FAA Remote Pilot sUAS Study Guide (FAA-G-8082-22).
Why is the wind stronger at 350 ft than at my launch point?
Friction. The Handbook says friction between the wind and the terrain slows the wind, with a stronger effect over rougher terrain and in stronger wind. The frictional drag normally decreases with height and becomes insignificant above the lowest few thousand feet. The Pilot's Handbook puts the effect inside about 2,000 ft of the ground, where the wind direction also differs from the wind a few thousand feet up.
A free question in the app uses this: a 6-knot wind at the launch point and a planned flight at 350 ft AGL. The expected answer is a stronger wind aloft.
Worked example
Reading the surface wind
Say a METAR shows 15006KT and you plan a roof inspection at 350 ft AGL. The airport sensor is not at your site. Expect more wind at the working height, possibly with a different direction, and gusts if buildings or trees upwind disturb the flow. Check the manufacturer's wind limit, and watch the drone's ground speed on the return leg, when it flies into the wind it was pushed along by.
Part 107 does not set a wind limit. It requires you to assess local weather conditions (107.49(a)(1)) and limits groundspeed to 87 kt (107.51(a)), so the practical limit is your aircraft's and your own.
Sources (checked 2026-11-14): FAA Aviation Weather Handbook (FAA-H-8083-28B, 2026); FAA Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25C); 14 CFR 107.49 (eCFR); 14 CFR 107.51 (eCFR).
How do buildings and terrain make turbulence?
The Pilot's Handbook and the study guide say ground topography and large buildings break up the flow of wind and create gusts that change rapidly in direction and speed. The intensity depends on the size of the obstacle and the wind speed. The Handbook adds surface roughness and the stability of the air: higher speed and rougher surfaces give more turbulence, and eddies carry farther downwind in stable air because they fade slowly.
For a drone working near a tall building, expect a gust-prone wake on the downwind side and corner effects at the roofline. On a ridge, the study guide says the wind flows smoothly up the windward side, then follows the terrain down the lee side where it gets increasingly turbulent, with a downward push that grows with wind speed. Stay clear of the lee side when the wind is strong.
Sources (checked 2026-11-14): FAA Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25C); FAA Remote Pilot sUAS Study Guide (FAA-G-8082-22); FAA Aviation Weather Handbook (FAA-H-8083-28B, 2026).
How do thermals and uneven heating affect low-level flight?
The Pilot's Handbook explains that plowed ground, rocks, sand and barren land absorb solar energy quickly and give off a lot of heat, while water, trees and vegetation heat more slowly. The uneven heating creates small convective currents. Updrafts are likely over pavement or barren ground and downdrafts over water or large stands of vegetation. The Handbook calls these thermals when the air is too dry for cumulus to mark them, and says a pilot has little or no indication until the turbulence arrives. Convection is strongest on warm summer afternoons when winds are light, and strength can vary a lot over short distances.
A drone flying from a parking lot toward a lake or a wooded slope can pass from rising air to sinking air within a few hundred feet. Where the job allows, plan the flight pattern to stay over uniform ground.
Sources (checked 2026-11-14): FAA Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25C); FAA Aviation Weather Handbook (FAA-H-8083-28B, 2026).
What are mountain waves and rotors?
When a stable air mass is forced up and over a ridge in a strong enough wind, a wave can form downwind. The Handbook describes two kinds: vertically propagating waves, and trapped lee waves. Lenticular clouds mark the crests when there is enough moisture, but severe wind events can happen with little or no visual warning. A rotor zone often forms near or below ridge level, under a wave crest, and can bring severe to extreme shear and turbulence. Strong downslope winds can reach gusts of 100 kt on lee slopes in extreme cases and end abruptly at a "jump" that is an area of extreme turbulence.
| Source | Rule of thumb for mountain wind |
|---|---|
| FAA study guide | Wind at mountaintop level above 25 kt suggests some turbulence; above 40 kt across a barrier calls for caution |
| Aviation Weather Handbook | Wind of 20 kt or greater at ridge level means moderate or greater turbulence, strong up- and downdrafts and rotor zones for low-level flight |
The two numbers differ because the sources describe different situations, so use the more cautious one. Convective clouds on the windward side mean unstable air, and turbulence close to the mountain on either side. Standing lenticular or rotor clouds mean a mountain wave and turbulence many miles to the lee.
Sources (checked 2026-11-14): FAA Aviation Weather Handbook (FAA-H-8083-28B, 2026); FAA Remote Pilot sUAS Study Guide (FAA-G-8082-22).
How do sea breezes and land breezes create shear?
These are local winds driven by differences in heating. In the daytime land warms faster than water, air rises over the land and cooler air flows in from the sea: a sea breeze, blowing sea to land. At night the land cools faster, and the flow reverses to a land breeze, usually weaker. The Handbook says a sea breeze front, the leading edge of the cooler marine air, often produces a wind shift and more cumulus along it, and can trigger showers and thunderstorms.
On a coastal job the wind can shift when the front passes, even when speeds are light. A variable wind or sudden wind shift can turn a headwind into a tailwind quickly, even at low speeds. Lake breezes work the same way around large lakes in the afternoon.
Sources (checked 2026-11-14): FAA Aviation Weather Handbook (FAA-H-8083-28B, 2026); FAA Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25C).
What is the gust rule in a METAR?
A gust is a rapid fluctuation of 10 kt or more between peaks and lulls. In a METAR, 27020G35KT means wind from 270 at 20 kt with gusts to 35. 180V240 after the wind group means the direction varied by 60 degrees or more in the last two minutes, with speed above 6 kt. A peak-wind remark such as PK WND 28045/15 tells you the highest wind since the last report and when it occurred. A WSHFT remark (with FROPA if a front passed) marks a wind shift. See the cheat sheet. A TAF can also forecast non-convective LLWS with a group such as WS020/27055KT, meaning shear from the surface up to 2,000 ft with wind 270 at 55 kt at that level.
Sources (checked 2026-11-14): FAA Aviation Weather Handbook (FAA-H-8083-28B, 2026); AIM Chapter 7, Section 1: Meteorology.
What does this mean for a drone flight plan?
- Compare the forecast and observed wind with your aircraft's limit, then add a margin for gusts.
- Look for a nearby front, thunderstorm or inversion in the forecast. These are the shear makers.
- Fly from the upwind side of obstacles when possible, and keep the aircraft out of the lee of buildings and ridges.
- Do a short check hover and a climb to working height before the job starts and watch how the aircraft is held by the wind.
- Bring the aircraft down when the gusts exceed what you can fly with confidence, or when a squall line, shelf cloud or dust wall approaches.
See also thunderstorms and microbursts for the convective version of shear and weather for drone pilots.
Free practice questions on this topic
1 original questions from the Sectional Cue bank. Try each one, then open the answer.
Surface friction
1. A remote pilot measures a 6-knot wind at the launch point and plans to fly at 350 ft AGL. What should the pilot expect aloft?
- Probably a stronger wind, since friction slows wind near the ground
- A weaker wind, since wind speed dies off with height above ground
- The same wind, since wind does not change in the first 400 ft
Show answer and explanation
A. Probably a stronger wind, since friction slows wind near the ground
Friction with terrain, trees and buildings slows the wind near the surface, so wind speed usually increases with height above the ground. Assuming the wind weakens with height has the effect backwards. Wind often changes noticeably within the first few hundred feet.
Source: PHAK (FAA-H-8083-25C), Chapter 12
Related guides
- Thunderstorms and microbursts: what drone pilots need to know
- Atmospheric stability and clouds for the Part 107 test
- Fronts and pressure systems for Part 107 pilots
- Weather for drone pilots: what the Part 107 test expects
- All Part 107 guides
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Sectional Cue has 1150+ original questions with explanations, 27 FAA figures you can tap to read, and timed 60-question rehearsals. About 152 questions and three chart lessons are free.
Sources
- FAA Aviation Weather Handbook (FAA-H-8083-28B, 2026), checked 2026-11-14
- FAA Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25C), checked 2026-11-14
- FAA Remote Pilot sUAS Study Guide (FAA-G-8082-22), checked 2026-11-14
- 14 CFR 107.49 (eCFR), checked 2026-11-14
- 14 CFR 107.51 (eCFR), checked 2026-11-14
How this page was made: written by Certloom Learning from the sources above, with the rules checked against the current regulation text. Practice items are original questions from the app's reviewed bank. Spot an error? certloomlearning@gmail.com.