NCAA PPL Meteorology cheat sheet

Standard atmosphere: sea-level pressure 29.92 inHg (1013.2 hPa), temperature 15 °C, lapse rate 2 °C per 1,000 ft up to the tropopause; pressure altitude uses 29.92 in the altimeter setting window.

Altimeter setting rule: flying from high pressure toward low pressure without resetting the altimeter causes the aircraft to fly lower than indicated; the error equals roughly 1,000 ft per 1 inHg of setting change.

Temperature affects altimeter and performance: cold air shrinks the pressure levels, so the true altitude is lower than indicated - apply cold-temperature altitude corrections when operating near terrain in winter.

Density altitude rises about 120 ft per 1 °C above standard at a given pressure altitude; high density altitude degrades takeoff, climb, and propeller/engine performance.

Ceiling is the height of the lowest broken or overcast layer; sky cover reporting uses FEW (1-2 oktas), SCT (3-4), BKN (5-7), OVC (8), with VV used for obscured skies.

Standard cloud bases from surface temperature and dew point: base (ft AGL) ≈ (temperature − dew point in °C) × 400; a 10 °C spread gives bases near 4,000 ft.

METAR wind is reported in degrees true and speed in knots; gusts appear as G (e.g., 27015G25KT), VRB indicates variable direction, and 00000KT means calm.

METAR visibility is in statute miles (e.g., 10SM); the remark group RMK may contain sea-level pressure (SLP), peak wind, and variable visibility that are not part of the body report.

Stable air produces stratiform clouds, steady precipitation, smooth air, and haze; unstable air produces cumuliform clouds, showery precipitation, turbulence, and good visibility between showers.

Temperature inversion traps moisture and haze below it, gives smooth air, and can create wind shear at the inversion top; fog often forms under a nocturnal inversion.

Icing risk: structural icing requires visible moisture and temperatures between 0 °C and about −20 °C; freezing rain is the most dangerous because supercooled drops freeze on impact rapidly.

Carburetor icing can occur at outside air temperatures between roughly −7 °C and +21 °C with high relative humidity; carburetor heat raises the mixture temperature and can initially worsen roughness.

Thunderstorm life cycle: cumulus (updrafts), mature (updrafts and downdrafts, hail, lightning, heaviest rain), dissipating (downdrafts). Avoid the mature stage entirely.

Microburst and gust front: a downdraft spreading along the surface produces a headwind then tailwind shear on approach, causing a sudden airspeed loss and sink; go around if encountered.

Fog types: radiation fog forms on clear, calm nights over land; advection fog forms when warm moist air moves over a cold surface; upslope fog forms as air is forced up terrain.

Mountain wave signs: lenticular clouds, rotor clouds, standing waves, and strong vertical drafts; expect severe turbulence on the lee side and downdrafts near ridges.

Frontal weather: cold fronts bring rapid passage, narrow bands of heavy showers, wind shift, and improving visibility after; warm fronts bring gradual lowering ceilings, wide precipitation, and poor visibility ahead.

Wind shear is a change in wind speed or direction over a short distance; report and expect it near fronts, thunderstorms, inversions, and surface obstructions.

Coriolis effect and friction: surface wind crosses isobars toward low pressure; aloft, wind blows nearly parallel to the isobars (geostrophic flow).

Buys Ballot's law: in the Northern Hemisphere, standing with your back to the wind puts low pressure on your left; this aids orientation relative to pressure systems.

Pressure gradient force: the closer the isobars, the stronger the wind; widely spaced isobars indicate light winds.

TAF structure: valid period, wind, visibility, weather, sky condition, then FM (rapid change), TEMPO (temporary), or BECMG (gradual change) groups; TAFs use statute miles in the US.

AIRMET covers moderate hazards (moderate turbulence, moderate icing, sustained winds ≥30 kt, IFR conditions, mountain obscuration); SIGMET covers severe or extreme hazards.

Convective SIGMETs address thunderstorms, hail ≥3/4 inch, and tornadoes; they are issued for areas of at least 3,000 square miles and imply severe turbulence and icing.

Pilot reports (PIREP) provide the only direct in-flight observation of turbulence, icing, and cloud tops; the UA/ UUA header distinguishes routine and urgent reports.

Wind direction aloft is reported in degrees true; surface winds in ATIS and METAR are in degrees true, but tower and AWOS voice broadcasts commonly give magnetic direction.

Standard lapse rate is 2 °C per 1,000 ft; the freezing level can be estimated by dividing the surface temperature in °C by 2 and multiplying by 1,000 ft.

Relative humidity is the ratio of actual moisture to the maximum the air can hold at that temperature; warmer air holds more water vapor, so cooling raises RH toward saturation.

Dew point is the temperature to which air must cool to reach saturation; when temperature and dew point are within about 2-3 °C, expect fog or low clouds.

Fog forms when the temperature-dew point spread narrows and the air cools to saturation; radiation fog typically dissipates 1-3 hours after sunrise as the surface warms.

Hail forms in cumulonimbus with strong updrafts that carry drops above the freezing level repeatedly; hail indicates severe turbulence and a hazard to aircraft.

Icing types: clear (rime-free, from large supercooled drops, spreads and is hard to remove), rime (rough, from small drops), and mixed; clear ice is the most hazardous.

Static electricity and lightning: stay clear of cumulonimbus by at least 20 nautical miles; lightning can strike outside the visible precipitation area.

Wind chill and heat stress affect the pilot and ground crew but not aircraft performance directly; density altitude, not wind chill, governs takeoff and climb performance.

Aircraft performance rule of thumb: a 10 °C temperature increase raises density altitude by about 1,200 ft, reducing takeoff and climb performance noticeably.

A METAR ceiling below 1,000 ft or visibility below 3 statute miles defines IFR conditions; VFR requires 3 SM visibility and cloud clearance per airspace class.

VFR cloud clearance in Class E below 10,000 ft MSL: 3 SM visibility, 1,000 ft above, 500 ft below, 2,000 ft horizontal from clouds.

In Class B airspace, VFR minimums are 3 SM visibility and clear of clouds; Class C and D require 3 SM and 1,000 above, 500 below, 2,000 horizontal.

Class G VFR minimums vary with altitude and time of day; at night above 1,200 ft AGL, 3 SM visibility and standard cloud clearance apply, while lower levels may allow 1 SM.

Mountain obscuration is reported when clouds hide terrain; AIRMET Sierra warns of mountain obscuration by clouds, precipitation, or fog.

Temperature inversion and wind shear: expect a shear layer at the top of a strong surface-based inversion, often producing a sudden airspeed change on climb-out or approach.

Altimeter errors: an altimeter set to a pressure higher than actual reads high; flying from high to low pressure without resetting causes the aircraft to be lower than indicated.

Cold front passage: wind shifts clockwise, temperature drops, pressure rises, and visibility improves; pre-frontal squall lines can produce severe turbulence and wind shear.

Warm front passage: pressure falls, temperature rises gradually, ceilings lower, and steady precipitation with reduced visibility occurs ahead of the surface front.

Density altitude = pressure altitude + 120 × (OAT − ISA temperature at that pressure altitude); use it for all takeoff, climb, and landing distance calculations.

Pressure altitude = indicated altitude + (29.92 − altimeter setting in inHg) × 1,000 ft; a lower altimeter setting yields a higher pressure altitude.

True altitude = indicated altitude + (OAT − ISA temperature) × 1,000 × 0.004 ft per degree; cold temperatures mean the aircraft is lower than indicated.

Cloud base estimate: base (ft AGL) = (surface temperature − dew point in °C) × 400; use the spread at the surface for convective cloud bases.

Freezing level estimate: divide the surface temperature in °C by 2 and multiply by 1,000 ft; this assumes the standard lapse rate to the freezing level.

Wind shear airspeed change: a 30 kt tailwind-to-headwind change on final changes indicated airspeed by 30 kt almost instantly; expect significant sink if not corrected.

Relative humidity = (actual vapor pressure / saturation vapor pressure) × 100; saturation occurs when RH reaches 100% and the temperature equals the dew point.

Standard atmosphere pressure at altitude: about 1 inHg per 1,000 ft near sea level; pressure halves roughly every 18,000 ft, which is why altimeters need a setting.

Visibility conversion: 1 statute mile ≈ 1.6 km ≈ 0.87 nautical mile; METAR in the US reports statute miles, while many international reports use meters.

ATIS provides current altimeter, wind, visibility, sky condition, and runway information; copy the altimeter setting and verify it against the current METAR before approach.

AWOS and ASOS automated stations report wind, visibility, sky condition, temperature, dew point, and altimeter; ASOS includes additional sensors and can report precipitation type.

A ceiling is reported as BKN or OVC; VV indicates an obscured sky and means the ceiling is indefinite, often from fog or heavy precipitation.

Ceiling and visibility are the primary IFR/VFR decision factors; a forecast of BKN008 means a ceiling at 800 ft AGL, below basic VFR minimums.

TAF amendments and AIRMETs are issued when conditions differ from forecast; a TAF is not an observation and must be compared with current METARs before flight.

Convective SIGMET implies severe or greater turbulence, severe icing, and low-level wind shear; avoid the entire area, not just the depicted cells.

Wind shear and microburst alerts from LLWAS or onboard systems require an immediate go-around; do not attempt to fly through a microburst.

Temperature-dew point spread below 5 °C with cooling overnight favors fog; check TAF and METAR trends for visibility reductions near sunrise.

Cold-temperature restricted performance: at airports below about −10 °C, apply cold-temperature altitude corrections to minimum vectoring altitudes and approach minimums per chart notes.

Stable air and haze: a stable layer traps smoke and haze, reducing visibility; unstable air mixes and disperses pollutants, improving visibility.

Thunderstorm hazards: hail, lightning, severe turbulence, icing, microbursts, and tornadoes; avoid by at least 20 NM and do not attempt to fly beneath a storm.

Squall line: a line of active thunderstorms often ahead of a cold front; it can produce severe wind shear and turbulence along its entire length.

Icing forecast: AIRMET Zulu covers moderate icing; SIGMET covers severe icing; known icing conditions require deicing or anti-icing equipment.

Rime ice forms in stratiform clouds with small supercooled droplets; clear ice forms in cumuliform clouds with large droplets and is more hazardous.

Fog dissipation: radiation fog burns off after sunrise as surface heating mixes the air; advection fog persists until the wind shifts or the air mass changes.

Wind direction reporting: METAR and TAF use degrees true; ATIS and tower voice reports often use degrees magnetic; verify the reference before using the value.

Pressure tendency: a rapid pressure fall indicates an approaching low or front; a rapid rise indicates improving conditions behind a front.

Mountain wave turbulence: strongest on the lee side of ridges near the tropopause; expect severe turbulence, downdrafts, and lenticular clouds.

Standard atmosphere: pressure 29.92 inHg, temperature 15 °C, lapse rate 2 °C per 1,000 ft; use it as the baseline for all performance calculations.

Altimeter setting: set to the local altimeter setting before flight; flying from high to low pressure without resetting causes the aircraft to be lower than indicated.

Density altitude: pressure altitude corrected for nonstandard temperature; high density altitude reduces takeoff, climb, and landing performance.

Ceiling: the height of the lowest broken or overcast layer; VV indicates an obscured sky and an indefinite ceiling.

METAR: surface observation with wind, visibility, weather, sky condition, temperature, dew point, and altimeter; remarks may include sea-level pressure and peak wind.

TAF: forecast of wind, visibility, weather, and sky condition; FM, TEMPO, and BECMG groups indicate timing and type of change.

AIRMET: moderate hazards including turbulence, icing, IFR conditions, mountain obscuration, and sustained winds of 30 kt or more.

SIGMET: severe or extreme hazards including severe turbulence, severe icing, and volcanic ash; convective SIGMETs address thunderstorms and hail.

PIREP: pilot report of actual in-flight conditions; the only direct observation of turbulence, icing, and cloud tops.