Title: FlightPerformanceCalc Aviation / Weather & METAR
Tags: weather-metar

Tag: METAR
Question: What are the parts of a METAR, in order?
Answer: Type, station (ICAO ident), day/time (Zulu), wind, visibility, weather, sky condition, temperature/dewpoint, altimeter, then remarks (RMK). Example: METAR KJFK 121853Z 18012KT 10SM FEW050 28/19 A2992 RMK AO2.
Ref: WEATHER · 01

Tag: METAR
Question: How is the date/time reported? Decode "121853Z".
Answer: Two-digit day of the month plus four-digit time in UTC/Zulu. 121853Z = the 12th at 1853 Zulu.
Ref: WEATHER · 02

Tag: Wind
Question: Decode the wind group "24016G28KT".
Answer: Wind from 240° true at 16 knots, gusting to 28 knots. VRB = variable direction; 00000KT = calm; a group like 180V240 in remarks shows variable direction limits.
Ref: WEATHER · 03

Tag: Visibility
Question: Decode visibility "1 1/2SM", "10SM", and "M1/4SM".
Answer: Prevailing visibility in statute miles: 1.5 SM, 10 (or more) SM, and less than 1/4 SM. M means "less than."
Ref: WEATHER · 04

Tag: Sky
Question: List the METAR sky-cover codes and their coverage in oktas (eighths).
Answer: SKC/CLR = clear, FEW = 1–2/8, SCT (scattered) = 3–4/8, BKN (broken) = 5–7/8, OVC (overcast) = 8/8. Heights are in hundreds of feet AGL (BKN035 = 3,500 ft).
Ref: WEATHER · 05

Tag: Sky
Question: What defines a "ceiling"?
Answer: The height AGL of the lowest BROKEN or OVERCAST layer (or the vertical visibility into an obscuration). FEW and SCT layers are not ceilings.
Ref: WEATHER · 06

Tag: Temp
Question: Decode temperature/dewpoint "M04/M07" and "28/19".
Answer: Temperature/dewpoint in °C, M = minus. So −4°C/−7°C, and 28°C/19°C.
Ref: WEATHER · 07

Tag: Pressure
Question: Decode the altimeter group "A2992".
Answer: Altimeter setting 29.92 inHg. Standard sea-level pressure is 29.92 inHg (1013.2 hPa).
Ref: WEATHER · 08

Tag: Temp
Question: What does a small temperature–dewpoint spread tell you?
Answer: The air is near saturation (high humidity). A spread within a few degrees means fog, mist, or low clouds are likely — expect reduced visibility and ceilings.
Ref: WEATHER · 09

Tag: Weather
Question: What do the intensity/proximity prefixes "-", "+", and "VC" mean?
Answer: "-" = light, no sign = moderate, "+" = heavy, and VC = in the vicinity (5–10 SM from the field, not at it).
Ref: WEATHER · 10

Tag: Weather
Question: Decode common weather codes: RA, SN, DZ, TSRA, FG, BR, FZRA, GR, HZ.
Answer: RA rain, SN snow, DZ drizzle, TSRA thunderstorm with rain, FG fog, BR mist, FZRA freezing rain, GR hail, HZ haze. Descriptors add detail: SH showers, TS thunderstorm, FZ freezing, BL blowing.
Ref: WEATHER · 11

Tag: TAF
Question: METAR vs TAF — what's the difference?
Answer: A METAR reports OBSERVED current conditions at an airport (issued about hourly). A TAF is a FORECAST for roughly a 5 SM radius of the airport, usually valid 24–30 hours.
Ref: WEATHER · 12

Tag: Categories
Question: Give the ceiling/visibility limits for VFR, MVFR, IFR, and LIFR.
Answer: VFR: ceiling > 3,000 ft AND vis > 5 SM. MVFR: 1,000–3,000 ft and/or 3–5 SM. IFR: 500 to < 1,000 ft and/or 1 to < 3 SM. LIFR: < 500 ft and/or < 1 SM.
Ref: WEATHER · 13

Tag: Minimums
Question: Basic VFR weather minimums in Class B airspace?
Answer: 3 SM flight visibility and remain CLEAR OF CLOUDS.
Ref: WEATHER · 14

Tag: Minimums
Question: VFR visibility and cloud clearance in Class C, D, and E below 10,000 ft MSL?
Answer: 3 SM visibility; stay 500 ft below, 1,000 ft above, and 2,000 ft horizontally from clouds. Mnemonic: "3-152."
Ref: WEATHER · 15

Tag: Minimums
Question: VFR minimums in Class E at or above 10,000 ft MSL?
Answer: 5 SM visibility; 1,000 ft below, 1,000 ft above, and 1 SM horizontally from clouds (aircraft go faster up high, so bigger margins).
Ref: WEATHER · 16

Tag: Minimums
Question: VFR minimums in Class G, daytime, at or below 1,200 ft AGL?
Answer: 1 SM visibility and clear of clouds. At night, or higher up, the requirements increase (generally 3 SM and 152 cloud clearance).
Ref: WEATHER · 17

Tag: Atmosphere
Question: State the standard atmosphere (ISA) sea-level values and lapse rates.
Answer: 15°C and 29.92 inHg (1013.2 hPa) at sea level. Temperature lapses about 2°C per 1,000 ft; pressure drops about 1 inHg per 1,000 ft.
Ref: WEATHER · 18

Tag: Atmosphere
Question: What is density altitude and why does it matter?
Answer: Pressure altitude corrected for nonstandard temperature — the altitude the airplane "feels." High density altitude (hot, high, humid) means less lift and thrust: longer takeoff rolls and weaker climb.
Ref: WEATHER · 19

Tag: Remarks
Question: What does "RMK" begin, and what is the difference between AO1 and AO2?
Answer: RMK begins the remarks section. AO2 = an automated station WITH a precipitation discriminator; AO1 = automated WITHOUT one.
Ref: WEATHER · 20

Tag: Visibility
Question: What is RVR and how is it reported?
Answer: Runway Visual Range — visibility measured down a specific runway by a transmissometer, reported in feet (e.g., R06/2400FT). Used in low-visibility operations.
Ref: WEATHER · 21

Tag: Fog
Question: Name the main fog types a pilot should recognize.
Answer: Radiation (clear, calm nights), advection (warm moist air over a cool surface, needs wind), upslope (moist air forced up terrain), steam fog (cold air over warm water), and freezing fog (FZFG).
Ref: WEATHER · 22

Tag: Stability
Question: What is a temperature inversion, and why care?
Answer: Temperature increases with altitude instead of decreasing — very stable air. It traps haze/smoke (poor visibility), gives smooth air, and can cause fog and low-level wind shear.
Ref: WEATHER · 23

Tag: TAF
Question: Decode the TAF change groups FM, BECMG, and TEMPO.
Answer: FM = a rapid change FROM a stated time. BECMG = a gradual, lasting change over a period. TEMPO = temporary fluctuations lasting under an hour each, expected less than half the period.
Ref: WEATHER · 24