Wind, Microbursts & Storm Hazards
~11 min read · Respect gust fronts, microbursts, and terrain rotors — the winds that take drones down.
Wind is invisible until it is throwing your aircraft around. The exam focuses on where dangerous wind hides: downwind of obstacles, inside and beneath thunderstorms, and in the microburst — the small, violent downdraft that reverses direction on you in seconds.
Mechanical turbulence and obstruction wind
Wind flowing over buildings, tree lines, hangars, and terrain breaks into eddies and rotors on the downwind (lee) side — reaching many obstacle-heights downstream. For low-altitude sUAS work, this is the most common hazard: approach paths that cross a building's lee side get sink, shear, and rotor turbulence. Stronger wind and sharper obstacles make sharper eddies. In mountains, strong winds across ridges form standing rotors capable of overwhelming any small aircraft.
- Turbulence collects on the LEE (downwind) side
- Effects extend well downstream of the obstacle
- Plan approaches on the upwind side of structures
Thunderstorm winds and gust fronts
A mature thunderstorm exports hazards far beyond its rain shaft: the gust front — the leading edge of cold outflow — can strike 15+ NM ahead of the storm with sudden shifts of 40+ knots, followed by the storm's downdrafts, hail, and lightning. The rule the exam rewards: stay well clear (guidance for aircraft is roughly 20 NM from severe storms), and for drone crews, be on the ground before the gust front arrives — not when the rain does.
- Gust front runs ahead of the storm — the first hazard to arrive
- Wind shifts are abrupt in both direction and speed
- Lightning and hail extend outside the visible cloud
Microbursts
A microburst is a concentrated downdraft under a convective cell, typically less than 1 NM across, lasting about 15 minutes, with downdrafts up to ~6,000 ft/min and horizontal outflow gusts to 45 knots. Crossing one produces the killer sequence: headwind (performance rises) → downdraft (sink) → tailwind (performance collapses). Dry microbursts fall from high-based clouds with rain evaporating before the ground (virga) — little visual warning beyond a dust ring.
Worked example
You are mapping a site with a high-based cumulus cell 5 NM west showing virga. Surface wind at your location swings from 8 kt easterly to 25 kt gusting westerly within a minute, and dust rises in a ring near the cell. Continue the grid?
Read the signs: virga under a high-based cell is the dry-microburst signature; the dust ring marks outflow hitting the ground; your abrupt wind reversal is the gust front or outflow boundary arriving. A small multirotor caught in the downdraft core can be driven into the ground faster than full power can arrest. The answer at exam level and field level is identical: land immediately, secure the aircraft, and wait out the cell — outflow events are short (≈15 minutes) but unsurvivable at 200 ft AGL. Resume after winds stabilize and the cell moves off.
Common exam pitfalls
Judging a thunderstorm by its rain shaft.
The gust front arrives miles ahead of the rain. Sudden wind shift + temperature drop = outflow is on you.
Trusting a dry sky under a high cloud base.
Virga (evaporating rain) is the dry microburst's calling card — the downdraft still reaches the ground as wind.
Flying the lee side of structures in gusty wind.
Rotors and sink concentrate downwind of obstacles; keep approaches and orbits on the upwind side.
Lee side lurks, gust front leads, virga warns: microburst below.
Recap
- Mechanical turbulence forms on the downwind side of obstacles and terrain
- Gust fronts strike far ahead of the storm with violent shifts
- Stay well clear of thunderstorms; land before outflow arrives
- Microburst: <1 NM, ~15 min, headwind→downdraft→tailwind sequence
- Dry microbursts show virga and dust rings, little else
- Wind reversal + temperature drop = outflow boundary, land now
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