Weather

14% of the Part 107 test · blueprint FAA-S-ACS-10B (April 2021)

Short answer

Area III is 11–16% of the Part 107 test. It covers weather sources — METAR, TAF, forecasts — and how to read them; density altitude and its effect on performance; wind, gusts and wind shear; temperature–dew point spread and fog; fronts and thunderstorms; icing; and how each condition affects a small unmanned aircraft's ability to fly safely within Part 107 minimums.

Why it matters on this exam

Expect at least one METAR to decode and one performance question about density altitude. Both are fast if you have drilled the format.

Key concepts (ACS Tasks III.A–III.B)

METAR (routine, hourly) and SPECI (special); TAF (24–30 h forecast for an airport). Times are UTC; winds are true direction in knots; visibility in statute miles; cloud heights AGL; altimeter inHg.
Ceiling = lowest broken (BKN) or overcast (OVC) layer, or vertical visibility (VV).
Density altitude rises with high temperature, high elevation, low pressure and high humidity; higher density altitude = less lift and thrust, longer climb, shorter battery endurance.
Wind: gusts, wind shear near fronts and thunderstorms, mechanical turbulence downwind of buildings and trees.
Fog: forms when temperature and dew point converge (spread ≤ 2 °C); radiation fog on clear calm nights, advection fog when warm moist air moves over cool surfaces.
Thunderstorm stages: cumulus, mature (rain begins), dissipating; hazards include downdrafts, hail, lightning; stay well clear.
Fronts: cold fronts bring fast-moving unstable weather; warm fronts bring low ceilings and steady precipitation.
Icing: visible moisture + temperature near or below freezing; disastrous for rotor performance.

Common mistakes

Reading cloud heights as MSL (they are AGL in a METAR).
Assuming a hot day at sea level has a low density altitude (heat alone raises it).

Worked example

METAR shows 18/17: spread 1 °C. Fog or low cloud is likely; check the sky group for a ceiling below your planned altitude and reconsider VLOS.

Original practice questions

WeatherDifficulty 2/5

In the METAR 'KDEN 211753Z 08012G20KT 10SM SCT045 BKN110 18/M02 A3011', what is the ceiling?

A4,500 ft AGL
B11,000 ft AGL
CNo ceiling; sky is scattered
D110 ft AGL

Show answer and rationale

Correct: B. A ceiling is the lowest broken (BKN) or overcast (OVC) layer or vertical visibility. SCT045 is scattered (not a ceiling); BKN110 is broken at 11,000 ft AGL, so that is the ceiling.

A — Scattered layers do not constitute a ceiling.
C — A broken layer is present, so there is a ceiling.
D — Cloud heights are in hundreds of feet: 110 = 11,000 ft.

WeatherDifficulty 2/5

The METAR wind group '08012G20KT' means:

AWind from 080° magnetic at 12 mph
BWind variable at 12 kt
CWind from 080° true at 12 kt, gusting to 20 kt
DWind from 120° at 8 kt, gusting 20

Show answer and rationale

Correct: C. METAR winds are reported as true direction (first three digits) and speed in knots, with G indicating gusts: from 080° at 12 knots gusting 20.

D — Direction is the first three digits (080).
A — METAR winds are true, not magnetic, and in knots.
B — Variable winds are shown as VRB.

WeatherDifficulty 3/5

Which combination produces the highest density altitude and the poorest sUAS performance?

AHigh pressure and low humidity at sea level
BCold, dry air at high pressure
CLow temperature, low elevation, high pressure
DHigh temperature, high elevation, low pressure, high humidity

Show answer and rationale

Correct: D. Density altitude increases with heat, elevation, low pressure and humidity; thinner air reduces rotor lift and motor cooling, shortening endurance and climb capability.

C — Those conditions lower density altitude.
A — High pressure lowers density altitude.
B — Cold dense air improves performance.

All 4 Weather questions →

Tools for this topic

METAR decoder and trainer — Paste any METAR or SPECI and see each field decoded — station, time, wind and gusts, visibility, weather phenomena, cloud layers and ceiling, temperature/dew point spread, altimeter — with four sample reports to drill on.

2 flashcards for Weather

Practice this topic

Blueprint-mapped questions with full rationales for every choice.

Start practice

Primary references

Remote Pilot – Small Unmanned Aircraft Systems Airman Certification Standards (FAA-S-ACS-10B, April 2021) — Federal Aviation Administration (FAA) · government · retrieved 2026-09-21, verified 2026-09-21
Advisory Circular 00-45H, Aviation Weather Services (METAR/TAF formats) — Federal Aviation Administration (FAA) · government · retrieved 2026-09-21, verified 2026-09-21

Last reviewed: 2026-09-21Next review by: 2026-11-20Draft — pending editorial reviewHow we verify facts