3.2 Wind, Turbulence, and Wind Shear

3.2 Wind, Turbulence, and Wind Shear

Wind is one of the most immediate weather hazards for drone operations. Understanding wind patterns, turbulence sources, and wind shear helps you plan safe operations and make in-flight decisions.

Surface Wind vs. Wind Aloft

• Surface wind is measured at 33 feet (10 meters) AGL by weather stations
• Wind direction is always reported as the direction the wind is coming FROM (a "north wind" blows from north to south)
• Surface winds are affected by friction with terrain — winds aloft are typically stronger
• Wind speed increases with altitude due to reduced surface friction
• Rule of thumb: wind at 2,000-3,000 ft AGL may be 2-3 times the surface wind speed

Wind Direction Reporting

Exam Tip: METARs and TAFs report wind direction relative to magnetic north. Winds aloft reports use true north.

Turbulence Types

Mechanical Turbulence:

• Caused by wind flowing over and around obstacles (buildings, terrain, trees)
• Most severe on the leeward (downwind) side of obstacles
• Creates unpredictable eddies and vortices near the surface
• Drone impact: Sudden attitude changes, loss of control near structures

Convective Turbulence (Thermal Turbulence):

• Caused by uneven heating of the Earth's surface
• Warm surfaces (parking lots, bare soil) create updrafts; cool surfaces (water, forests) create downdrafts
• Most common on warm, sunny afternoons
• Drone impact: Altitude variations, unexpected climb/descent

Frontal Turbulence:

• Occurs along weather fronts where air masses of different temperatures meet
• Most severe along cold fronts and squall lines
• Can be extreme near thunderstorms
• Drone impact: Severe, potentially catastrophic — avoid operations near fronts

Wake Turbulence:

• Generated by all aircraft in flight (rotorcraft and fixed-wing)
• Helicopter rotor wash is particularly dangerous for small drones
• Drone impact: Can cause complete loss of control if a drone enters the wake of a manned aircraft

Wind Shear

Wind shear is a sudden change in wind speed and/or direction over a short distance:

• Horizontal wind shear: Change in wind across a horizontal distance
• Vertical wind shear: Change in wind at different altitudes
• Can occur at any altitude but is particularly dangerous near the surface
• Associated with frontal boundaries, thunderstorms, temperature inversions, and terrain features

Microburst:

• A localized, intense downdraft from a thunderstorm
• Creates a divergent wind pattern at the surface (outflow)
• Wind speeds can exceed 45 knots in a microburst
• Can last 5-15 minutes
• Extremely dangerous for all aircraft, including drones

Wind Effects on Drone Operations

Crosswind Operations

When wind is perpendicular to your drone's path:

• The drone must crab (angle) into the wind to maintain its intended track
• GPS-equipped drones do this automatically, but it increases power consumption
• Strong crosswinds can make precise hovering difficult near structures